Showing papers in "Conservation Biology in 1992"

Disturbance, Diversity, and Invasion: Implications for Conservation

Abstract: Preservation of natural communities has historically consisted of measures protecting them from physical disturbance. Timber harvests and livestock grazing are usually excluded from preserves, and fire suppression has been practiced—within the U.S. system of national parks, for example. Ecologists and conservationists have come to recognize, however, that many forms of disturbance are important components of natural systems. Many plant communities and species are dependent on disturbance, especially for regeneration (Pickett & White 1985). Preserves should be large enough to allow the natural disturbance regime to operate and to support a mosaic of patches in different stages of disturbance, successional recovery, and community maturation (Pickett & Thompson 1978).

Biodiversity and Ecological Redundancy

Abstract: This paper addresses the problem of which biota to choose to best satisfy the conservation goals for a particular region in the face of inadequate resources. Biodiversity is taken to be the integration of biological variability across all scales, from the genetic, through species and ecosystems, to landscapes. Conserving biodiversity is a daunting task, and the paper asserts that focusing on species is not the best approach. The best way to minimize species loss is to main- tain the integrity of ecosystem function. The important ques- tions therefore concern the kinds of biodiversity that are sig- nificant to ecosystem functioning. To best focus our efforts we need to establish how much (or how little) redundancy there is in the biological composition of ecosystems. An ap- proach is suggested, based on the use offunctional groups of organisms defined according to ecosystem processes. Func- tional groups with little or no redundancy warrant priority conservation effort. Complementary species-based ap- proaches for maximizing the inclusion of biodiversity within a set of conservation areas are compared to the func- tional-group approach.

Natural Capital and Sustainable Development

Abstract: A minimum necessary condition for sustainability is the maintenance of the total natural capital stock at or above the current level. While a lower stock of natural capital may be sustainable, society can allow no further decline in natural capital given the large uncertainty and the dire consequences of guessing wrong. This “constancy of total natural capital” rule can thus be seen as a prudent minimum condition for assuring sustainability, to be relaxed only when solid evidence can be offered that it is safe to do so. We discuss methodological issues concerning the degree of substitutability of manufactured for natural capital, quantifying ecosystem services and natural capital, and the role of the discount rate in valuing natural capital. We differentiate the concepts of growth (material increase in size) and development (improvement in organization without size change). Given these definitions, growth cannot the sustainable indefinitely on a finite planet. Development may be sustainable, but even this aspect of change may have some limits. One problem is that current measures of economic well-being at the macro level (i.e., the Gross National Product) measure mainly growth, or at best conflate growth and development. This urgently requires revision. Finally, we suggest some principles of sustainable development and describe why maintaining natural capital stocks is a prudent and achievable policy for insuring sustainable development. There is disagreement between technological optimists (who see technical progress as eliminating all resource constraints to growth and development) and technological skeptics (who do not see as much scope for this approach and fear irreversible use of resources and damage to natural capital). By maintaining natural capital stocks (preferably by using a natural capital depletion tax), we can satisfy both the skeptics (since resources will be conserved for future generations) and the optimists (since this will raise the price of natural capital depletion and more rapidly induce the technical change they predict).

Movement Corridors: Conservation Bargains or Poor Investments?

Abstract: Corridors for movement of organisms between refuges are confounded with corridors designed for other functions, obscuring an assessment of cost-effectiveness. The rationales for movement corridors are (1) to lower extinction rate in the sense of the equilibrium theory, (2) to lessen demographic stochasticity, (3) to stem inbreeding depression, and (4) to fulfill an inherent need for movement. There is a paucity of data showing how corridors are used and whether this use lessens extinction by solving these problems. Small, isolated populations need not be doomed to quick extinction from endogenous forces such as inbreeding depression or demographic stochasticity, if their habitats are protected from humans. In specific instances, corridors could have biological disadvantages. Corridor proposals cannot be adequately judged generically. In spite of weak theoretical and empirical bases, numerous movement corridor projects are planned. In the State of Florida, multi-million-dollar corridor proposals are unsupported by data on which species might use the corridors and to what effect. Similarly, plans for massive corridor networks to counter extinction caused by global warming are weakly supported. Alternative approaches not mutually exclusive of corridors might be more effective, but such a judgment cannot be made without a cost-benefit analysis. Los corredores para el movimiento de organismos entre refugios son confundidos con corredores designados para otras funciones obscureciendo una evaluacion sobre costo-efectividad. Las funciones atribuidas a los corredores para movimiento son (1) disminuir la tasa de extincion definida en terminos de la teoria de equilibrio, (2) disminuir la estocasticidad demografica, (3) contrarrestar la depresion endogamica y (4) satisfacer una necesidad innata de movimiento. Existe una carencia de datas que demuestren como son usados estos corredores y si este uso minimiza las extinciones al resolver estos problemas. Poblaciones pequenas y aisladas no estan necesariamente condenadas a una rapida extincion causada por fuerzas endogenas, como depresion endogamica o estocasticidad demografica, si sus abitats estan protejidos de los humanos. En instancias particulares, los corredores pueden tener desventajas biologicas. Las propuestas sobre corredores no pueden serjuzgadas apropiadamente en forma generica. Numerosos corredores para movimiento estan proyectados a pesar de fundamentos teoricos y empiricos debiles. En el estado de Florida, propuestas multimillionarias para corredores no estan fundamentadas por datos que indiquen que especies usarian los corredores y con que proposito lo harian. En forma semejante los proyectos de redes masivas de corredores para contrarrestar la extincion causada por el calentamiento global estan pobremente fundamentados. Estrategias alternativas, que no son mutuamente excluyentes con los corredores, podrian ser mas efectivas pero tales juicios no pueden ser hechos sin un analisis de costobeneficio.

Forest Fragmentation and Alien Plant Invasion of Central Indiana Old‐Growth Forests

Abstract: We assessed alien plant invasion of old-growth forest islands in rural central Indiana by means of paired sample sites along “warm” (south and west) edges and “cool” (north and east) edges in each of seven forest remnants. In general, the fragments appeared resistant to alien invasion; alien species richness and frequency dropped sharply inward from forest edges, and forest interiors were relatively free of aliens. However, aliens were more diverse and more frequent on warm edges than on cool ones. The main factor limiting invasion is probably low light availability in forest interiors, though limited dispersal and low disturbance levels may also be important. We suggest that invasion is discouraged by the edge response of the forests themselves: development of a dense wall of bordering vegetation that reduces interior light levels and wind speeds. The most successful invaders are mostly escaped ornamentals or other species not commonly found in adjoining fields. They can be expected to become more prominent in the future, but their spread at the landscape scale may be slowed by the “oceans” of cropland surrounding these forest islands.

World‐Wide Species Richness Patterns of Tiger Beetles (Coleoptera: Cicindelidae): Indicator Taxon for Biodiversity and Conservation Studies

Abstract: The family of tiger beetles (Cicindelidae) is an appropriate indicator taxon for determining regional patterns of biodiversity because (1) its taxonomy is stabilized; (2) its biology and general life history are well understood, (3) individuals are readily observed and manipulated in the field, (4) the family occurs world-wide and in a broad range of habitat types; (5) each species tends to be specialized within a narrow habitat; (6) patterns of species richness are highly correlated with those of other vertebrate and invertebrate taxa; and (7) the taxon includes species of potential economic importance. Logistical advantages provide some of the strongest arguments for selecting tiger beetles as an appropriate indicator taxon. Species numbers of tiger beetles are relatively well known for 129 countries. Eight countries alone account for more than half the world total of 2028 known species. Species numbers are also indicated for eleven biogeographical zones of the world. For gridded squares across North America, the Indian subcontinent, and Australia, species richness of tiger beetles, birds, and butterflies shows significant positive correlations. However, tiger beetle species numbers can be reliably determined within fifty hours on a single site, compared to months or years for birds or butterflies, and the advantage of using tiger beetles in conservation biology is evident La familia de los escarabajos tigre (Cicindelidae) constituye un taxon indicador apropiado para determinar patrones regionales de biodiversidad porque (1) su taxonomia es estable; (2) su biologia e historia natural son bien conocidas; (3) los individuos son facilmente observables y manipulables en el campo; (4) la familia tiene una amplia distribucion mundial, asi como un gran variedad de habitats; (5) cada especie tiende a especializarse dentro de un habitat restringido; (6) los patrones de riqueza de especies estan altamente correlacionados con los de otros taxones de vertebrados e invertebrados; y (7) el taxon incluye especies de potencial importancia economica. Las ventajas logisticas de los escarabajos tigre proporcionan una de las evidencias mas solidas para considerarlos un taxon indicador apropiado. El numero de especies de escarabajos tigre es bien conocido en 129 paises. Ocho de estos paises contienen mas de la mitad de las 2028 especies conocidas en el mundo. Tambien se indica el numero de especies para once zonas biogeograficas del mundo. Mediante el estudio de cuadriculas de muestreo situadas en Norte America, el Subcontinente Indio y Australia, que ilustran la riqueza de especies de escarabajos tigre, aves y mariposas, se observa una correlacion positiva significativa. Sin embargo, el numero de especies de escarabajos tigre puede determinarse confiablemente mediante unas cincuenta horas de muestreo en un solo sitio, en comparacion con los meses o anos que se necesitan para aves o mariposas, pro lo que la ventaja de utilizar los escarabajos tigre en conservacion biologica es obvia.

Dispersal Can Limit Local Plant Distribution

Abstract: The ability of species to establish new popuiations at unoccupied sites is a critical feature in the maintenance of biological diversity, and it has taken on new importance as a result of global climate change and expected changes in species distributior~ To examine the dispersal potential of plant specie~ seeds of four annual piant species were exper- imentally dispersed 40 to 600 m from existing populations in Massachusetts (U.Xik ) to 34 nearby unoccupied but ap- parently suitable siteg At three of these site~ new popula- tions were established that persisted for four generations and expanded slowly in area At seven site~ a small tnttial pop- uiation eventually died out At the 24 other siteg new pop- ulatiom did not become established, indicating that the sites were in some way unsuitabl¢ that not enough seeds arrived, or that conditions suitable for seed germination do not oc- cur every year. These results suggest that some species may be unable to disperse naturally out of their existing ranges in response to global climate changg particularly if habitat fragmentation creates barriers to dispersal These species may have to be assisted to reach suitable sites nearby to prevent their extinction in the wild.

Alien Flora in Grasslands Adjacent to Road and Trail Corridors in Glacier National Park, Montana (U.S.A.)

Abstract: Alien plant species have rapidly invaded and successfully displaced native species in many grasslands of western North America Thus, the status of alien species in the nature reserve grasslands of this region warrants special attention This study describes alien flora in nine fescue grassland study sites adjacent to three types of transportation corridors—primary roads, secondary roads, and backcountry trails—in Glacier National Park, Montana (USA) Parallel transects, placed at varying distances from the adjacent road or trail, were used to determine alien species richness and frequency at individual study sites Fifteen alien species were recorded, two Eurasian grasses, Phleum pratense and Poa pratensis, being particularly common in most of the study sites In sites adjacent to primary and secondary roads, alien species richness declined out to the most distant transect, suggesting that alien species are successfully invading grasslands from the roadside area In study sites adjacent to backcountry trails, absence of a comparable decline and unexpectedly high levels of alien species richness 100 m from the trailside suggest that alien species have been introduced in off-trail areas The results of this study imply that in spite of low levels of livestock grazing and other anthropogenic disturbances, fescue grasslands in nature reserves of this region are vulnerable to invasion by alien flora Given the prominent role that roadsides play in the establishment and dispersal of alien flora, road construction should be viewed from a biological, rather than an engineering, perspective Nature reserve man agers should establish effective roadside vegetation management programs that include monitoring, quickly treating keystone alien species upon their initial occurrence in nature reserves, and creating buffer zones on roadside leading to nature reserves Resumen: Especies de plantas introducidas han invadido rapidamente y desplazado exitosamente especies nativas en praderas del Oeste de America del Norte Por lo tanto el estado de las especies introducidas en las reservas de pastizales naturales de esta region exige especial atencion Este estudio describe la flora introducida en nueve pastizales naturales de festuca, las areas de estudios son adyacentes a tres tipos decorredores de transporte—caminos primarios, caminos secundarios y senderos remotos—en el Parque Nacional “Glacier,” Montana (EEUU) Para determinar riqueza y frecuencia de especies introducidas, se trazaron transectas paralelas, localizadas a distancias variables del camino o sendero adyacente en las areas de estudio Se registraron quince especies introducidas Dos pastos eurasiaticos, Phleum pratensis y Poa pratensis, resultaron particularmente abuntes en la mayoria de las areas de estudio En lugares adyacentes a caminos primarios y secundarios, la riqueza de especies introducidas disminuyo en la direccion de las transectas mas distantes, sugiriendo que las especies introducidas estan invadiendo exitosamente las praderas desde areas aledanas a caminos En las areas de estudio adyacentes a senderos remotos no se encontro una disminucion comparable; inesperados altos niveles de riqueza de especies introducidas a 100 m de los senderos, sugieren que las especies foraneas han sido introducidas desde otras areas fuero de los senderos Los resultados de este estudio implican que a pesar de los bajos niveles de pastoreo y otras perturbaciones antropogenicas, los pastizales de festuca en las reservas naturales de esta region son vulnerables a la invasion de la flora introducida Dada el rol preponderante que juegan los caminos en el establecimiento y dispersion de la flora introducida, la construccion de rutas debe ser vista desde un punto de vista biologica, mas que desde una perspectiva meramente ingenieril Los administradores de reservas naturales deberian establecer programas efectivos de manejo de vegetacion en los bordes de los caminos Estos programas deberian incluir monitoreo, tratamiento rapido de especies introducidas y claves tan pronto como se detecten en las reservas naturales, y creacion de zonas de transicion en los caminos que conducen a las reservas naturales

Influence of Selective Logging on Bird Species Diversity in a Guianan Rain Forest

Abstract: The composition and structure of the bird com- munity were investigated in French Guiana (northeastern Amazonia) I year and 10 years after selective logging and compared with bird community composition and structure in undisturbed primary forest A point-count method was used in which 937 0.25-ha sample quadrats were censused for 20 minutes each. Whereas logging removed little more than 3 trees/ha, 38% of the forest undergrowth was destroyed and a higher proportion of the canopy was opened or dam- aged. An overall 27-33% decrease of species richness, fre- quency, and abundance occurred after logging with a less marked decline of diversity and evenness indices, a substan- tial increase in the proportion of dominant species, and a 45% difference in species composition, weighed by fre- quency, between logged and undisturbed forest communi- ties. Forty-two percent of the species from the primary forest decreased sharply or disappeared after logging and only 34% increased or remained unchanged. Microhabitat selection was the main correlate of sensitivity to disturbance. Most affected by logging were species associated with the under- story of tall mature stands especially terrestrial species, members of mixed flocks, and solitary sallying insectivores, all of which decreased by 70% to over 90%. Most birds as- sociated with canopy, small gaps, and vine tangles declined by only 10-30%. Small frugivores and species associated with clearings or edges increased. Among other factors, phys-

Rethinking the Stock Concept: A Phylogeographic Approach

Abstract: The “stock” is the fundamental population unit of legally mandated conservation efforts, yet its formal definition in the scientific literature and in two U.S. conservation acts is varied and so general that attempts to apply it in practice are arbitrary. Because choice of stocks deserving management protection is sometimes politically contentious, improvement of the working definition is important. A key element should be the degree to which a population can be considered an evolutionarily significant unit. We propose that a hierarchial classification scheme be applied to stock designations. Category I populations, having the highest probability of being evolutionarily significant units, are characterized by a discontinuous genetic divergence pattern where locally adapted and closely related genome assemblages are separated from others geographically and by significant genetic distances. Category II populations are similarly characterized by significant genetic diversity, but with weak geographic partitioning. Category III populations are the converse of II, having little genetic differentiation between assemblages that are clearly separate and likely to be reproductively isolated. Category IV assemblages have the lowest probability of being evolutionarily significant units and are characterized by extensive gene flow and no subdivision by extrinsic barriers. In addition to phylogeographic designation, the following information is used in the classification, as indicated by single-letter abbreviations: distribution (a), population response (b), phenotypic (c), and genotypic (d) information. Included are evidence both for and against designating population as a separate stock. In the designation “Type II a/bc,” for example, information to the right of the solidus would be evidence for “lumping,” to the left would be for “splitting.” Missing letter abbreviations would signify lack of reliable data. Note that phylogeographic designation depends on the results of selection operating to produce a locally adapted genome (indicated by differences in demographic, phenotypic, and genotypic measures) and on gene flow (indicated by differences in distribution or by movement data). Hierarchial stock categorization allows resource managers to direct limited resources to the populations most deserving of protection, that is, the populations that are most likely to be evolutionarily significant units. Using this comprehensive classification of stock allows preliminary, conservative splitting of assemblages where data are lacking without the danger that these divisions will become entrenched as biological dogma.

Rates of Deforestation in Los Tuxtlas, a Neotropical Area in Southeast Mexico

Abstract: On the basis of ground surveys, aerial photographs (for 1967 and 1976), and satellite imagery (for 1986), maps of rain forest distribution were developed for the northern part of the Sierra de Los Tuxtlas (Veracruz, southeast Mexico). Forest coverage maps for 1967, 1976, and 1986 show dramatic deforestation proceeding up from the lowlands, with the remaining natural vegetation now increasingly restricted to the high, steep, and less accessible parts of the Sierra. From the digitizing of the maps it was estimated that (1) during the nearly 20 years of this analysis the vegetation was reduced by 56%, and (2) by early 1986, approximately 84% of the original forest area had been lost. The derived annual deforestation rates (expressed as the percentage of remaining forest that is cleared per year) were 4.2% for the interval 1967–1976 and 4.3% for 1976–1986. Were these trends and rates to continue, only 8.7% of the original vegetation would persist by the year 2000, and then only in the form of an archipelago of very small forest fragments of which the largest would be the now-protected areas (e.g, the Los Tuxtlas Biological Station with only 640 ha), and the most inaccessible tracts. Immediate action is urgently needed to protect these small but rich remnants and preserve them as foci of potential biological inocula for future ecorestoration of these, the northernmost tropical forests on the continent.

Do Appalachian herbaceous understories ever recover from clearcutting

Abstract: Life history characteristics of many herbaceous understory plants suggest that such species recover slowly from major perturbations such as clear cutting. We examined herbaceous cover and richness in the understories of nine primary (“old-growth”) forests in the southern Appalachian Mountains and of nine comparable secondary forests, ranging in age from 45 to 87 years since clear cutting. Neither cover nor richness increased with age in the secondary forests. This suggests three possibilities: (1) that recovery is so slow or variable among sites that 87 years is insufficient time to detect it; (2) that such forests will never recover to match remnant primary forests because climatic conditions are different today than when the forests became established; or (3) that herbaceous plants colonize pit and mound microtopography caused by the death of trees, so that recovery must await the growth, death, and decomposition of the trees of the secondary forest. Whatever the mechanism, herbaceous understory communities in the mixed-mesophytic forests of the Appalachians appear unlikely to recover within the present planned logging cycles of 40–150 years, suggesting a future loss of diversity of understory herbaceous plants. Resumen: Las caracteristicas del periodo de vida de numerosas plantas herbaceas, sugiere que estas especies se recuperan lentamente de grandes perturbaciones como la tala debosques. Nosotros examinamos la cubierta herbacea y abundancia en el sotobosque de nueve bosques primarios (antiguo crecimiento) en los Montes Apalaches del Sur, y los comparamos con nueve bosques secundarios que no han sido talados por periodos que van de 45 a 87 anos. La riqueza y la abundancia no han aumentado con el tiempo en el bosque secundario. Esto sugiere tres posibilidades: (1) que la recuperacion es tan lenta o variable entre sitios que 87 anos resultan insuficientes para detectarla, (2) que este tipo de bosques nunca se recuperara al nivel de los bosques primarios originales, ya que las condiciones climaticas actuales son diferentes a las existentes cuando los bosques fueron originariamente establecidos, o (3) que plantas herbaceas colonizan la microtopografia del suelo que ha sido removido a causa de la descomposicion de los arboles muertos, y por consiguiente la recuperacion debe esperar el crecimiento, muerte y descomposicion de los bosques secundarios. Cualquiera sea el mecanismo, la cubierta herbacea de las comunidades de bosques mesofiticos mixtos en los Apalaches, no parece estar recuperandose dentro del ciclo previsto para la tala de arboles que es de 40 a 150 anos. Esto sugiere una perdida futura en la diversidad de las plantas que conforman la cubierta herbacea.

Using Montane Mammals to Model Extinctions Due to Global Change

Abstract: We use data on the species-area relationship and the nested subset structure of the boreal mammal faunas inhabiting isolated mountaintops in the Great Basin to develop a simple quantitative model that predicts the number and identity of species that would go extinct under an assumed scenario of changing climate and vegetation. Global warming of 3°C is predicted to cause the loss of 9–62% of the species inhabiting each mountain range and the extinction of three of fourteen species throughout the region. These results suggest (1) that it is possible to make highly plausible predictions about the susceptibility of species to extinction without detailed information about their population biology, and (2) that global and regional environmental changes seriously threaten the survival of species that are restricted in distribution to both natural “habitat islands” and biological reserves. Usando datos acerca de la relacion especie-area y la estructura en subgrupos anidados que caracteriza a la fauna de mamiferos boreales que habitan los picos montanosos aislados en “Great Basin,” desarrollamos un modelo quantitativo que predice el numero e identidad de las especies que se extinguirian bajo un supuesto escenario de cambios en clima y vegetacion. Se predice que un calentamiento global de 3°C causaria la perdida de un 9–62% de las especies que habitan cada cadena montanosa y la extincion de tres de las 14 especies a traves de la region. Estos resultados sugieren que: (1) es posible hacer predicciones con un alto grado de seguridad acerca de la suceptibilidad de las especies a la extincion, sin contar con una detallada informacion acerca de sus biologias poblacionales, y (2) que cambios ambientales tanto globales como regionales, amenazan seriamente la supervivencia de las especies, cuya distribucion se encuentra restringida tanto a “habitat insulares” de caracter natural como a reservas biologicas.

A Dynamic Analysis of Northern Spotted Owl Viability in a Fragmented Forest Landscape

Abstract: The Northern Spotted Owl (Strix occidentalis cau- rina) is closely associated witb mature and old-growth co- niferous forests in the Pacific Northwest There has been a rapid loss and fragmentation of this habitat over the last half century, which may jeopardize tbe long- term survival of the species through reduction of dispersal success. In this paper we report results of a population model for the North- ern Spotted Owl that incorporates both juvenile dispersal and search for mates. We analyze both deterministic and stochastic versions of the model in search of thresholds for population persistence related to search efficiency, popula- tion density, and amount of suitable habitat. In addition, we analyze the model under the nonequilibrium conditions tbat currently exist due to timber harvest in the owls' pre- ferred habitat. Our results predict a sharp threshold below which populations cannot persist, and suggest tbat infer- ences from population models that incorporate equilibrium assumptions may be highly misleading.

Assessing the Economic Value of Traditional Medicines from Tropical Rain Forests

Abstract: In recent years, increasing attention has been given to the value of the tropical rain forest as a source of nontimber market products. Although estimates exist for the value of select forest products (Peters et al. 1989; Tobias and Mendelsohn 1990), many have yet to be quantified. One important class of products that has not yet been valued is tropical pharmaceuticals. Several recent essays have noted that tropical forests are a rich source of unknown chemicals that may eventually prove useful to medicine (Abelson 1990; Oldfield 1989). In addition, traditional medicines are currently the basis for much of the primary health care delivered in tropical nations (Farnsworth et al. 1985). For example, traditional practitioners provide up to 75% of the primary health care needs of rural people in Belize (R. Arvigo, personal communication). Local forests are the source of the plants processed into therapies used in traditional medical systems (Balick 1990). In this paper, we quantify the value of the forests for their therapeutic products, using data from Belize, Central America. Current methods for the harvest of medicinal plants from forests and fallows involve both destructive and nondestructive practices. For example, destructive methods of harvest include stripping a tree completely of its bark, or cutting it to facilitate harvest. Removing the roots or tubers from a woody or herbaceous plant

Where Should Nature Reserves Be Located in the Cape Floristic Region, South Africa? Models for the Spatial Configuration of a Reserve Network Aimed at Maximizing the Protection of Floral Diversity

Abstract: The SLOSS debate can only be resolved by considering the optimal spatial configuration of a nature-reserve system. Only when target species have been identified by such considerations can the size of the constituent reserves be determined. We explored two null models for a spatial configuration of reserves in the Cape Floristic Region, South Africa, based on the distribution of species in the family Proteaceae (Angiospermae: Rosidae). In the first model, reserves (12 × 13 km grid squares) were assigned at random for comparison with existing, proposed, and theoretically ideal configurations. In the second model, the theoretically ideal reserve configuration was constructed using the first model as a preassigned configuration. Two methods were used to iteratively select a reserve from the grid system: richness of unprotected species (species-richness algorithm), and the sum of the rarity indexes for each unprotected species (rarity algorithm). Both algorithms yielded configurations requiring fewer reserves than those contained in proposed or existing configurations, although neither algorithm was perfect. The existing reserve configuration performed no better than the random model, assuming that the principal goal is protection of all species. We confirm that the best approach to designing a reserve configuration that maximizes the protection of species richness is to identify areas of high endemism and richness within particular biogeographical regions. Resumen: El debate “SLOSS” solo podra ser resuelto si se considera la configuracion espacial optima de un sistema de reservas naturales. El tamano de las reservas que constituiran el sistema no podra ser determinado sin antes haber identificado a las especies apropiadas basandose en las consideraciones antes mencionadas. Exploramos dos modelos nulos para la configuracion espacial de las reservas en la Region Floristica del Cabo, Sudafrica, en base a la distribucion de las especies de la familia de las Proteaceas (Angiospermae: Rosidae). En el primer modelo, las reservas (rectangulos de 12 × 13 km de lado) fueron asignadas al azar a los efectos realizar comparaciones con las configuraciones que existen actualmente, aquellas que han sido propuestas y finalmente con aquellas que son teoricamente ideales. En el segundo modelo, la configuracion teoricamente ideal fue construida usando el primer modelo como la configuracion preasignada. Se utilizaron dos metodos para seleccionar iterativamente una reserva del total existente en el sistema de cuadriculado: la riqueza de especies no protegidas (algoritmo riqueza de especies); y la suma del los indices de rareza para cada especie no protegida (algoritmo de rareza). Si bien ningun algoritmo fue perfecto, ambos dieron como resultado configuraciones que requieren un menor numero de reservas que las requeridas por configuraciones ya propuestas o existentes en la actualidad. Suponiendo que el objetivo principal es la proteccion de todas las especies, los resultados obtenidos usando la configuracion de las reservas existentes en la actualidad no fueron mejores que aquellos obtenidos usando el modelo aleatorio. Confirmamos que la mejor estrategia para disenar la configuracion de reservas que maximice la riqueza de especies es identificar areas con also endemismo y riqueza dentro de regiones biogeograficas particulares.

Habitat Variegation, An Alternative to Fragmentation

Abstract: A recent review in Conservation Biology by Saunders et al. ( 1991 ) examined the effects of habitat fragmentation on plant and animal communities and the implications of fragmentation for biological conservation. This paper comprehensively summarized research on a topic that has been a major focus for researchers in recent years. There are few countries in the world that have not experienced extensive and major modifications to their landscapes as a result of agriculture. However, the form of the modification can vary from region to region, and our experience suggests that the fragmentation model may not be applicable in all areas. The concept of fragmentation implies that habitat remnants are isolated by areas that function as hostile environments to the organisms within the remnants. Biota must rely either on connecting corridors of habitat or on long-distance dispersal to move between fragments or they remain stranded in them. There are many instances where this is the case, for example, remnant forests surrounded by wheat paddocks in Western Australia and vegetation reserves in urban areas. This concept of habitat distribution, however, is not applicable to all examples of agricultural development. On the northern tablelands of New South Wales, agriculture has modified most of the native vegetation, leaving only small areas in close to original condition. Nonetheless, grassy vegetation still dominates the landscape matrix in various states of modification. This requires a model that differs from the examples just cited, because the intervening areas are modified versions of the original ecosystems and do not present barriers to most native species, as they do in a fragmented landscape. The original vegetation of the tablelands before European settlement was predominantly eucalypt woodlands and forests with a grassy understory (Curtis 1989). Agricultural development has been pastorally based with extensive fertilization and some pasture "improvement" involving the sowing of introduced grasses and legumes. While some areas have lost virtually all their tree populations and most of their native understory species, natural pastures are still widespread and eucalypts are present in varying densities across the landscape. The most intact grassland vegetation tends to be concentrated in nature reserves and along roadsides. These areas are also subjected to varying degrees of modification from sheep and cattle grazing, earthworks, loss of native herbivores, etc. In terms of these human-induced changes, the variegated nature of the grassy ecosystems on the tablelands must be [utilized] differently by different taxa. At one extreme, there are native plants that grow successfully over the whole range of modifications and can be found at the majority of sites sampled (S. McIntyre, unpublished data). For these species, potential habitat forms a continuum across the landscape. The other extreme results from intolerance to most forms of interference; these species exist in a truly fragmented landscape, restricted to remnants in better condition. The majority of

Techno-Arrogance and Halfway Technologies: Salmon Hatcheries on the Pacific Coast of North America

Abstract: Humankind has adopted an arrogant and ultimately self-defeating attitude toward nature that places technological mastery over nature at the forefront of our approach to many environmental problems. This “techno-arrogance” fails to recognize limitations on, and ramifications of, attempted control of nature. An example of techno-arrogance is the flawed attempt to recover Pacific salmonid fisheries through technological application in the form of hatcheries. Countless salmon stocks have declined precipitously over the last century as a result of overfishing and widespread habitat destruction. A central feature of recovery efforts has been to build many hatcheries to produce large quantities of fish to restock streams. This approach addresses the symptoms but not the causes of the declines (an example of a halfway technology), because the habitats remain largely unsuitable for salmon. There are at least six reasons why the hatchery approach will ultimately fail: (1) data demonstrate that hatcheries are not solving the problem—salmon continue to decline despite decades of hatchery production; (2) hatcheries are costly to run, and divert resources from other efforts, such as habitat restoration; (3) hatcheries are not sustainable in the long term, requiring continual input of money and energy, (4) hatcheries are a genetically unsound approach to management that can adversely affect wild populations; (5) hatchery production leads to increased harvest of declining wild populations of salmon; and (6) hatcheries conceal from the public the truth of real salmon decline. I recommend that salmonid management turn from the symptoms to the causes of decline. Overharvest and habitat destruction must be directly addressed in a major, landscape-level effort, on a scale comparable to the hatchery program, if salmonid fisheries are to remain a part of the ecological recreational, commercial and asthetic arenas in the long term. La humanidad ha adoptado una actitud arrogante, y en ultima instancia destinada al fracaso, que pone a la maestria tecnologica por encima de la naturaleza en la vanguardia de nuestro ataque a muchos de los problemas ambientales. Esta arrogancia tecnologica falla en reconocer las limitaciones y las ramificaciones que tienen los intentos en controlar la naturaleza. Un ejemplo de arrogancia tecnologica es el intento fallido de recuperar las pesquerias salmoneras del Pacifico a traves de aplicaciones tecnologicas en forma de criaderos. Innumerables stocks de salmones han decrecido precipitadamente en la ultima centuria como resultado de la sobrepesca y la destruccion masiva de habitats. Una caracteristica central de los esfuerzos de recuperacion ha sido la construccion de numerosos criaderos a los efectos de producir grandes cantidades de peces para sembrar los rios. Esta estrategia esta dirigida a los sintomas pero no a las causas do la declinacion (un ejemplo de tecnologia a medio camino), puesto que los habitats permanecen en su mayoria-no aptos para el salmon. Existen por lo menos seis razones por las cuales la estrategia de criaderos esta, en ultima instancia, destinada al fracaso: (1) datos demuestran los criaderos no estan resolviendo el problema; el salmon continua declinando a pesar de decadas de produccion en los criaderos; (2) los criaderos son costosos en su operacion, y desvian recursos que podrian ser destinados a otros esfuerzos tales como la restauracion del habitat; (3) los criaderos no son sostenibles en el largo plazo, requiriendo un flujo continuo de dinero y energia; (4) los criaderos son una estrategia erronea desde un punto de vista genetico y pueden afectar adversamente a las poblaciones silvestres; (5) la produccion de los criaderos conlleva a un incremento en la cosecha de poblaciones silvestres de salmon; y (6) las estaciones de cria ocultan al publico las verdaderas causas de la declinacion de las poblaciones silvestres de salmon. Recomiendo que el manejo del salmon pase de los sintomas a las causas de la declinacion. La sobrepesca y la destruccion del habitat tienen que ser consideradas en un esfuerzo de grandes magnitudes a nivel paisajistico y a una escala comparable a la de las campanas de criaderos a los efectos de que las pesquerias de salmon continuen formando parte de las arenas ecologicas recreativas y comerciales en el largo plazo.

The Species Problem and Conservation: What are We Protecting?

Abstract: Although conservation biologists base most of their activities on species taxa, they have participated little in the debate of systematists and evolutionary biologists about the recognition and nature of species. It is clear from this debate that there is no agreement on what species are, how they should be delimited, or what they represent. But in conservation science, and particularly in the selection, design and management of protected areas, species are either treated as types or as evolutionary units. A typological view of species may lead to a failure to protect the real diversity of life in the long term, if conservation priorities are set on the basis of species numbers or on circumscriptions of endangered, threatened, or endemic species taxa that result from the use of different species concepts. Considering species as typological entities may also lead workers to disregard geographic variation and to neglect the problem of deciding which level of variability to protect. It may even affect the goal of maintaining the evolutionary potential of organisms, if the focus is placed on the preservation of a sample of the existing types in populations that will persist as little changed as possible. When species are considered as evolutionary units, attention is shifted from the level of species to that of populations and metapopulations. Problems may still arise if these populations are considered in the context of species taxa, particularly if their composition is managed or if indicator species are used. A closer interaction between systematists and conservation biologists is suggested. Although the pressures of time and the difficulties faced by conservation biologists cannot be denied, considering the species problem more critically may result in recognizing the limitations of the taxonomic information used; it may also contribute to the refinement of the concepts and methods involved in their activities, making them more congruent with the nature of biological diversity. Resumen: A pesar de que los biologos de la conservacion basan gran parte de sus actividades en taxa al nivel de especie su participacion en la discusion de sistematicos y evolucionistas sobre el reconocimiento y naturaleza de las especies ha sido limitada. Este debate ha puesto en evidencia que existe total desacuerdo sobre que son las especies, como deben delimitarse y que representan. Sin embargo, en biologia de la conservacion y, en particular, en la seleccion, diseno y manejo de areas protegidas, las especies son consideradas como tipos o como unidades evolutivas. Un enfoque tipologico de las especies puede implicar que no se logre proteger la diversidad biologica en el largo plazo, si las prioridades de conservacion se establecen a partir de numeros de especies, o de especies en peligro, amenazadas o endemicas, cuya delimitacion resulte del uso de diferentes conceptos de especie. Considerar a las especies como entidades tipologicas tambien puede llevar a que se ignore la variacion geografica y a que no se enfrente el problema de decidir el nivel de variabilidad a proteger. Puede aun afectar el objetivo de mantener el potencial evolutivo de los organismos protegidos, en la medida en que la conservacion se centre en preservar una muestra de los tipos existentes en poblaciones que persistan con un minimo de cambio. Cuando las especies son consideradas como unidades evolutivas, el foco de atencion se desplaza del nivel de especies al de poblaciones y metapoblaciones. Pero aun pueden presentarse problemas, si las poblaciones se consideran en el contexto de especies taxonomicas y, en particular si se maneja su composicion, o se utilizan especies indicadoras. Por lo tanto, se recomienda una mavor interaccion entre sistematicos y biologos de la conservacion. Aunque la presion del tiempo y las dificultades que enfrentan los biologos de la conservacion son innegables, el considerar el problema de las especies de una forma mas critica puede resultar en el reconocimiento de las limitaciones de la informacion taxonomica empleada. Igualmente, puede contribuir al refinamiento de los conceptos y metodos utilizados en sus actividades, para hacerlos mas acordes con la naturaleza de la diversidad biologica.

Use of Linkage Disequilibrium Data to Estimate Effective Size of Hatchery and Natural Fish Populations

Abstract: A primary parameter in the assessment of the viability of a population is its effective population size (Ne). Allozyme analysis of four groups of fishes provided data on linkage disequilibrium, which were then used to estimate Ne. The groups included hatchery samples of juvenile white seabass, Atractoscion nobilis, juvenile rainbow trout, Oncorhynchus mykiss, from the Shasta Hatchery, and juvenile chinook salmon, O. tshawytscha, from the Coleman National Fish Hatchery. The fourth sample consisted of juvenile chinook salmon from the threatened winter run in the upper Sacramento River. The groups of fish were chosen to represent different applications of the methodology to conservation of fishes. For a variety of reasons. Ne may be considerably lower than census counts of fish present in the parental populations. The Ne of the hatchery broodstock that produced the sample of juvenile white seabass was estimated to be approximately 10, although 25 adult white seabass were present in a mass spawning tank. Ne estimates for the parental populations of the Shasta and Coleman Hatchery samples were 35.8 and 132.5, respectively. The actual number of fish spawned at the Shasta Hatchery was approximately 40, whereas nearly 10,000 salmon were spawned at the Coleman Hatchery. The threatened winter run of chinook salmon had an estimated Ne of 85.5 and an approximate run size of 2000 salmon. The method of estimating effective population size from linkage disequilibrium data appears to result in realistic estimates of effective population size when adequate sample size and a sufficient number of polymorphic loci are available. Uno de los parametros fundamentales en la evaluacion de la viabilidad de poblaciones es su tamano poblacional efectivo (Ne). El analisis de alocimas en cuatro grupos de peces proveyo de datos sobre el desequilibrio de ligamiento que luego fueron usados para estimar Ne. Los grupos incluian muestras de Cherna Blanca juvenil, Atractoscion nobilis, y Trucha Arcoiris juvenil, Oncorhynchus mykiss, provenientes del criadero Shasta, y salmon “Chinook” juvenil, O. tshawytscha, provenientes del criadero “Coleman National Fish Hatchery”. La cuarta muestra consistio en juveniles del Salmon “Chinook” provenientes de cardumentes invernales amenazados del curso superior del rijo Sacramento. Los grupos de peces fueron elegidos en forma tal que representasen distintas aplicaciones de la metodologia destinada a la conservacion de peces. Debido a una variedad de razones, Ne puede ser considerablemente menor que el tamano censal de los peces presentes en las poblaciones paternales. El Ne del stock filial de la estacion de cria que produjo la muestra de juveniles de Cerna Blanca fue de aproximadamente 10, si bien el numero de Chernas Blancas adultas presentes en el tanque de desove masivo era 25. Las estimaciones de Ne de las pobalciones paternales de las muestras provenientes de los criaderos Shasta y “Coleman Hatchery,” fueron 35.8 y 132.5, respectivamente. El numero real de peces nacidos en el criadero Shasta fue aproximadamente 40, mientras que cerca de 10.000 salmones fueron procreados en el criadero “Coleman Hatchery”. Los cardumenes invernales del Salmon “Chinook” tuvieron un Ne estimado de 85.5 y un tamano de cardumen de aproximadamente 2.000 salmones. El metodo de estimacion de tamano poblacional efectivo a partir de datos de desequilibrio de ligamiento parece dar como resultado estimaciones nal efectivo cuando se usan tamanos muestrales adecuados y cuando un numero suficiente de loci polimorficos estan disponibles.

Mitochondrial DNA Variability of the Gray Wolf: Genetic Consequences of Population Decline and Habitat Fragmentation

Abstract: The gray wolf is a large, highly mobile predator whose original geographic range included most of the Northern Hemisphere. High rates of genetic exchange probably characterized even distantly-separated populations in the past, but recent population declines and habitat fragmentation have isolated previously contiguous populations, especially in the Old World. We examine mitochondrial DNA (mtDNA) variability among twenty-six populations of wolves from throughout their geographic range. We find eighteen mtDNA genotypes in gray wolves, seven of these are derived from hybridization with coyotes, four are confined to the New World, six are confined to the Old World and one is shared by both areas. Genetic differentiation among wolf populations is significant but small in magnitude. In the Old World, most localities have a single unique genotype, whereas in the New World several genotypes occur at most localities and three of the five genotypes are nearly ubiquitous. The pattern of genetic differentiation in the gray wolf contrasts with that of another large, highly vagile canid, the coyote, in which genetic differentiation among populations is not significant even among widely separated localities. We suggest that the difference between these two species reflects the rapid, recent increase in coyote numbers and expansion of their geographic range, and the coincident decline in gray wolf populations. Apparent genetic differences among extant wolf populations may be a recent phenomenon reflecting population declines and habitat fragmentation rather than a long history of genetic isolation. El lobo gris es un predador grande y altamente mobil cuyo distribucion geografica original abarcaba la mayor parte del Hemisferio Norte. Es muy probable que en el pasado, altas tasas de intercambio genetico caracterizaran, incluso, poblaciones muy distantes. Sin embargo, recientes declinaciones poblacionales y fragmentacion del habitat han aislado poblaciones que antiguamente se escontraban, contiguas, especialmente en el Viejo Mundo. Examinamos la variabilidad en el ADN mitocondrial (mtDNA) de 26 poblaciones de lobos existentes a lo largo de toda su area de distribucion geografica. Encontramos 18 genotipos de mtDNA en lobos grises, de estos 7 son derivados de hibridacion con coyote, 4 estan confinados al Nuevo Mundo, 6 estan confinados al Viejo Mundo y uno esta presente en ambas areas. La diferenciacion genetica entre poblaciones de lobos es significativa pero de pequena magnitud. En el Viejo Mundo, la mayoria de las localidades tienen un unico genotipo especifico para cada loalidad, mientras que en el Nuevo Mundo, la mayoria de las localidades poseen varios genotipos, y tres de los cinco son aproximadamente cosmopolitas. El patron de diferenciacion genetica en el lobo gris contrasta conaquel de otro canido grande y altamente movil, el coyote, en el cual la diferenciacion genetica entre poblaciones no es significativa incluso en el casode localidades muy distantes. Sugerimos que la diferencia entre estas dos especies refleja el rapido y reciente incremento en el numero de coyotes, la expansion en su distribucion geografica y la declinacion en las poblaciones de lobos grises que ocurrio coincidentemente. La diferenciacion genetica entre las poblaciones de lobos existentes en la actualidad, puede ser un fenomeno reciente que refleja, antes que una largo historia de aislamiento genetico, la declinacion poblacional y fragmentacion del habitat.

Mechanized Logging, Market Hunting, and a Bank Loan in Congo

Abstract: Financing for logging of tropical moist forests in the Republic of Congo is commonly sought in the form of loans from multilateral development banks. Pressure from nongovernmental conservation organizations and from within the banks themselves has resulted in their beginning to assess the environmental consequences of such loans. We conducted one of the first such assessments of an African Development Bank loan to a logging company. Geographic isolation, resulting transportation costs, and market demands have forced commercial loggers within the Sangha region of Congo to exploit only the most valuable timber. This form of timber extraction destroys an average of 6.8% of the canopy and thus, unlike clear cutting, was expected to have a minimal impact on wildlife populations. Line transect counts showed, however, that primate abundance was exceedingly low in logged forest. We believe this is not a direct consequence of canopy reduction, but results from the extremely intensive market hunting that coincides with timber surveying and extraction. Weapons and hunting camps were common, and logging company vehicles transported primates, duikers and other game daily. Wildlife laws of Congo are openly violated and they are not enforced. While market hunting is clearly facilitated and intensified by the presence of logging concessions, it is the Congo’s highly urbanized population that provides the ever growing demand for meat, a demand not being met through animal husbandry. Thus, although selective logging in the absence of hunting may have only limited adverse effects on wildlife, when the two are combined the consequences are grave for the Sangha region’s wildlife. Loans to logging companies from the African Development Bank should incorporate conditions for ensuring wildlife conservation. El financiamiento para la explotacion forestal de selvas tropicales humedas en la Republica del Congo proviene comunmente de prestamos otorgados por bancos multilaterales de desarrollo. Presiones provenientes de organizaciones no gubernamentales (ONGs) y de los mismos bancos, han dado como resultado comienzo a una evaluacion de las consecuencias ambientales de tales prestamos. Nosotros conducimos una de las primeras evaluaciones de este tipo, estudiando el impacto de un prestamo del Banco Africano de Desarrollo a una compania forestal. Aislamiento geografico, costos resultantes de transporte y demandas del mercado, han forzado a los aserraderos dentro de la region de Sangha, en el Congo, a explotar solamente la madera mas valiosa Esta forma de extraccion selectiva de la madera destruye en promedio un 6.8% del canopeo, de esta forma, contrariamente a la tala rasa, se esperaba un impacto minimo en las poblaciones naturales. Sin embargo, conteos a lo largo de transectas, demostraron que la abundancia de primates fue excesivamente baja en la selva talada. Creemos que esta situacion no es una consecuencia directa de la reduccion del canopeo, sino un resultado de la caceria comercial extremadamente intensiva que coincide con el reconocimento y extraccion de la madera. Campamentos de caza y armas eran comunes, los vehiculos de las companias taladoras transportaban diariamente primates, antilopes y otros productos de caza. Las leyes del Congoreferentes a la vida silvestre son abiertamente violados y no son ejecutadas. Mientras la caceria comercial es claramente facilitada e intensificada por la presencia de las concesiones para la tala del bosque, es la poblacion altamente urbanizada del Congo la que provee una creciente demanda por carne, demanda que no es satisfecha a traves de la cria de animales. Por consiguiente, si bien la tala selectiva en ausencia de caceria podria haber limitado los efectos adversos sobre la fauna, cuando las dos se combinan las consecuencias son graves para la vida silvestre de la region de Sangha. Los prestamos otorgados por el Banco de Desarrollo del Africa a las companias forestales tendrian que incorporar condiciones que aseguren la conservacion de la vida silvestre.

Fragmentation of Phragmites Habitats, Minimum Viable Population Size, Habitat Suitability, and Local Extinction of Moths, Midges, Flies, Aphids, and Birds

Abstract: Results from populations of insects and birds inhabiting Phragmites habitats were used to analyze effects of fragmentation. Flush-crash cycles of the stem-boring moth Archanara geminipuncta (Lepidoptera, Noctuidae) showed regionally concurrent, local extinctions despite an originally enormous population size (more than 180,000 adults), emphasizing the importance of metapopulation dynamics. Further, A. geminipuncta could be considered a keystone species, since shoot damage facilitated more than twenty species of herbivores, saprovores (of the caterpillars’ feces), and their parasitoids. The gall midge Lasioptera arundinis could survive only in side shoots induced by shoot damage of A. geminipuncta. Small Phragmites stands had thinner shoots (due to a water or nutrient deficiency) and shoots with more leaves (due to a better light supply) than large stands, thereby influencing species-specific demands for habitat suitability and nutritiousness of reed tissue. In other words significance of habitat fragmentation could not be assessed by area alone. For example, two chloropid flies depending on thin, yellowish shoots survived only in small habitats or in the unmown edges of large habitats. Local persistence of Phragmites herbivores depended on much larger population sizes than could be expected from a population size sufficient to maintain genetic variation. At least 11,000 adults of the gall midge Giraudiella inclusa (or more than 84,000 galls) were necessary to avoid local extinction. With regard to conservation management of reed habitats, nature reserves should consist of old and unmown reeds, have fewer disturbed (particularly, fewer mown) habitat edges, measure more than two hectares (priority should go to the largest remaining fragments), and be surrounded by nearby reed habitats providing reservoir populations and diverse shoot types. Resultados obtenidos a partir de poblaciones de insectos y aves que habitan ambientes de Phragmites fueron utilizados para analizar los efectos de la fragmentacion. A pesar de tamanos poblacionales originalmente enormes (180,000 adultos), ciclos de crecimiento explosivocolapso en la polilla Archanara geminipuncta (Lep., Noctuidae) mostraron extinciones locales concurrentes a escala regional. Este hecho enfatiza la importancia de la dinamica metapoblacional. Ademas, A. geminipuncta podria ser considerada una especie “keystone” (clave) dado que la ruptura de brotes facilio el establecimiento de mas de veinte especies de herviboros, saprofagos (de las heces de orugas) y sus parasitoides. El cagachin Lasioptera arundinis solo puede sobrevivir en el interior de brotes, inducido por la ruptura de brotes de A. geminipuncta. Rodales pequenos de Phragmites tuvieron brotes mas delgados (debido a una deficiencia en agua o nutrientes) y con mas hojas (debido a una mayor disponibilidad de luz) que rodales grandes, indluenciando por consiguiente las demandas especificas de cada especie por tejidos canizos, i.e. la importancia de la fragmentacion del habitat no puede ser evaluada solo en funcion del area. Por ejemplo, dos moscas cloropidas que dependen de brotes delgados y amarillentos solo sobrevivieron en habitats pequenos o en bordes sin segar de habitats grandes. La persistencia local de organismos herbivoros que se alimentan de Phragmites dependio de tamanos poblacionales mucho mas grandes que aquellos suficientes para mantener la variabilidad genetica. Se necesitaron por lo menos 11.000 adultos del cagachin Giraudiella inclusa (es decir, mas de 84.000 agallas)para evitar la extincion a nivel local. Con respecto al manejo de canaverales con fines conservacionistas, las reservas naturales deberian (i) consistir de canaverales viejos y sin segar, (ii) tener bordes poco perturbados y sin segar, (iii) medir mas de dos hectareas (se le debe asignar prioridad a los fragmentos mas grandes en existencia), y (iii) deben estar rodeadas por canaverales cercanos que provean poblaciones de reserva.

Rapid Loss of Genetic Variation in Large Captive Populations of Drosophila Flies: Implications for the Genetic Management of Captive Populations

Abstract: Levels of variation in eight large captive popula- tions of D. melanogaster (census sizes -5000) that had been

Toward a Theory of Inter-Refuge Corridor Design

Abstract: The accelerating fragmentation and isolation of wildlife populations as a consequence of habitat alteration has resulted in increased interest in the preservation of travel corridors between populations to minimize local extinction and genetic isolation (Harris 1984; Noss & Harris 1986). Landscape architects and other planners now frequently include such wildlife corridors in development designs. However, little work has been done on the theory underlying the parameters of effective corridors, and there are little data on the details of movements of animals through landscapes that would be useful to the development of corridor design. Except for riparian strips, natural corridors have rarely been mentioned in the literature (see Berger 1987). In this paper, I review natal dispersal patterns to begin to build a general theory of corridor design for mammals. I also make recommendations for future research and suggest minimum corridor widths for representative mammals.

Rarity and Vulnerability: The Birds of the Cordillera Central of Colombia

Abstract: The rarity of an organism is widely accepted as a good predictor of vulnerability, but rarity has been interpreted in a variety of ways. Rabinowitz et al. (1986) defined three dimensions of rarity for an analysis of the flora of the British Isles geographic distribution, habitat specificity, and local population size. They found the three factors to be independent, that is, each factor provides information not provided by the other two. In this paper, the method of Rabinowitz et al. is used to analyze the vulnerability of the cloud forest avifauna of the Cordillera Central of Colombia The method is extended by assigning a vulnerability index to each form of rarity and analyzing its taxonomic and ecological correlates. I found that the three factors are not independent. Species with wide geographic distribution tend to have broad habitat specificity and high population densities. One-third of the species have low population density, and most of these have restricted habitat specificity and narrow geographic ranges. Forty-five percent of the birds in this sample are highly vulnerable because they have narrow distributions and require forest habitats. The taxonomic and ecological analyses reveal that some groups of species are particularly vulnerable. Among insectivorous birds, woodcreepers, spinetails, and antbirds seem to be very vulnerable becuse they depend on forest habitats. Raptors show no clear pattern, but for frugivores a clear pattern emerges. Some families (e.g., parrots, cotingas), seem to be consistently vulnerable, independent of body size. Tanagers show a significant correlation between body size and vulnerability. An analysis of local vulnerability (determined by habitat specificity and population size, regardless of distribution) reveals that frugivorous birds of restricted habitat specificity are significantly larger. Similar findings have been reported by other studies. The three-dimensional classification of rarity used in this study provides a rapid, albeit preliminary, approach to identifying vulnerable species. To develop management practices adapted to each particular case, careful analysis of life history traits and detailed population and community studies are required. Resumen: La Rareza de un organismo es considerada un estimador util para predecir vulnerabilidad sin embargo rareza es un concepto que ha sido interpretado de distintas maneras. Rabinowitz, Cairns y Dillon (1986) definieron tres dimensiones de rareza en un analisis de la flora de las Islas Britanicas: Distribucion geografica, especificidad de habitat y tamano local de las poblaciones. Los autores encontraron que los tres factores son independientes, es decir, cada factor provee informacion no provista por los otros dos. En el presente trabajo, el metodo de Rabinowitz et al. es utilizado para analizar la vulnerabilidad de la avifauna de los bosques de niebla de la Cordillera Central de Colombia. El metodo es extendido asignando un indice de vulnerabilidad a cada forma de rareza, y analizando los factores ecologicos y taxonomicos correlativos. Se encontro que los tres factores no son independientes. Las especies con amplia distribucion geografica tienden a presentar extensa especificidad de habitat y altas densidades de poblacion. Un tercio de las especies presentan baja densidad poblacional. y la mayoria de ellas tienen restringida especificidad de habitat y rangos geograficos limitados. El 45% de las especies de aves en esta muestra son altamente vulnerables por tener una limitada distribucion geografica y requerir habitats boscosos. El analisis taxonomico y ecologico revela que algunos grupos de especies son particularmente vulnerables. Entre aves insectivoras, las familias Dendrocolaptidae, Furnariidae y Formicariidae, parecen ser muy vulnerables por su dependencia de los habitats boscosos. Las rapaces no muestran un patron claro, pero para las frugivoras emerge un patron claro. Algunas familias (e.g., loros, cotingidos) parecen ser consistentemente vulnerables, independientemente del tamano corporal. Los traupidos exhiben una correlacion significativa entre tamano corporal y vulnerabilidad. Un analisis de la vulnerabilidad local (determinada por especificidad de habitat y tamano de las poblaciones, independientemente de la distribucion geografica), revela que las aves frugivoras con especificidad de habitat restringido son significativamente mas grandes. Resultados similares han sido reportados por otros estudios. La clasificacion de rareza en tres dimensiones utlizada en el presente estudio provee un metodo rapido, aunque preliminar, para identificar especies vulnerables. Para el desarrollo de practicas de manejo adaptadas a cada caso en particular se requiere un analisis detallado de los rasgos de la historia de vida y un detallado estudio de las poblaciones y comunidades.

Sea Turtle Conservation and Halfway Technology

Abstract: How we define a problem often determines what we are willing to consider as a solution. When we define the impending extinction of a sea turtle species solely in terms of there being too few turtles, we are tempted to think of solutions solely in terms of increasing the numbers of turtles. Hence, some of our attempts to conserve sea turtles involve “halfway technology,” which does not address the causes of or provide amelioration for the actual threats turtles face. Programs such as headstarting, captive breeding, and hatcheries may serve only to release more turtle into a degraded environment in which their parents have already demonstrated that they cannot flourish. Furthermore, captive programs may keep turtles from serving important ecological functions in the natural environment, or place them at some disadvantage relative to their natural counterparts once released. Such programs can be contrasted with more appropriate technologies that directly address and correct particular problems encountered by sea turtles without removing them from their natural habitat. For example, installing turtle excluder devices in shrimp trawl nets will reduce mortality of adults and larger juvenile sea turtles, and using low pressure sodium lighting on beaches may prevent hatchlings and nesting females from becoming disoriented. In the final analysis, we need clean and productive marine and coastal environments. Without a commitment to such long term goals, efforts to protect sea turtles will be futile. Resumen: La forma en que definimos un problema, usualmente determinara que es lo que estamos dispuestos a aceptar como solucion. Cuando definimos la inminente extincion de la tortuga de mar, solamente en terminos de que quedan muyrpocas tortugas, nos vemos tentados a pensar en soluciones solamente en terminos de incrementar el numero de las mismas. Por consiguiente, alguna de las cosas que hacemos en nuestros intentos para conservar tortugas de mar involucra una “tecnologia a medias, ” que no considera las causas ni brinda medidas que tiendan a disminuir los peligros reales que las tortugas enfrentan. Programas como “headstarting” (cria de tortugas desde la etapa de huevo hasta unos 9 meses de edad, antes de liberarlas al medio ambiente), cria en cautiverio y viveros, serviran solamente para liberar mas tortugas a un medio ambiente deteriorado en el cual sus padres ya han demostrado que no pueden prosperar: Mas aun, programas de animales en cautiverio, podrian impedir que las tortugas cumplan importantes funciones ecologicas en su medio ambiente natural, o las colocarian en desventaja con respecto a sus contrapartes naturales una vez liberadas. Dichos programas pueden ser comparados con tecnologias mas apropiadas que dirijan y corrijan directamente problemas particulares que las tortugas de mar encuentran, sin sacarlas de su medio ambiente natural. Por ejemplo, la instalacion de dispositivos que excluyan las tortugas de las redes de pezca de camarones reducira la mortalidad de los adultos y de las tortugas juveniles de mayor tamano; el use de iluminacion de sodio de baja presion en playas, podria prevenir que las crias y las hembras se desorientasen. En concreto, lo que se necesita son ambientes costeros y marinos limpios y productivos. Sin un compromiso a largo plazo sobre dichos objetivos, los esfuerzos por protejer las tortugas de mar sera inutiles.

Recent invasions of the Gulf of Maine : three contrasting ecological histories

Abstract: Introduced species are common members of estuarine communities where their role as competitors and predators is of concern, This paper examines the invasion of Gulf of Maine benthic habitats by the ecologically similar alien invertebrates Styela clava, Botrylloides diegensis, and Membranipora membranacea. Styela clava increased slowly in abundance at study sites in Beverly, Massachusetts and Portsmouth, New Hampshire. We found no evidence of competitive dominance by S. clava, even though it is the competitive dominant in similar habitats elsewhere. Botrylloides diegensis rapidly became a dominant species after its arrival in the Great Bay Estuary, but this dominance was short-lived. B. diegensis persists in the estuary as an early colonist of primary space and as an epibiont on secondary substrates in established communities. Membranipora membranacea became the dominant epiphyte on laminarian kelps within two years. Although M. membranacea overgrew the native epiphytes Obelia geniculata and Electra pilosa in the overwhelming majority of encounters these native species are more common on other algal hosts. Therefore, competitive dominance is not likely a factor in the successful invasion of the Gulf of Maine by M. membranacea. These species provide evidence for opposing views of the role of competition in mediating community invasion. We show that ecological similarity among species is not an accurate criterion to predict either the mechanism of invasion or the means of persistence. In addition, these data indicate that biological invasions must be examined on broad spatial and temporal scales; short-term or narrowly focused studies can lead to incorrect conclusions.

Ecological Impacts of Introduced Animals in Nahuel Huapi National Park, Argentina

Abstract: In Nahuel Huapi National Park in southwestern Argentina, livestock and exotic deer pose important management problems. Due to the economic and social benefits of sport hunting and production of livestock, it is politically impractical to completely eradicate these animals from the park. Instead, park managers attempt to minimize the effects of these introduced animals by preventing their spread into more pristine parts of the park and by trying to diminish their population densities. Managers are also promoting the relocation of livestock production to appropriate sites in the National Reserve part of the park where livestock raising is permitted. Detailed information on the ecological impacts of introduced herbivores is needed both to guide management of the different vegetation types of the park and to support the park managers' public relations campaign justifying exotic animal control. We examined the ecological effects of introduced animals along the vegetation gradient from Andean rain forests through xeric woodlands to the Patagonian steppe. We sampled 30 stands for floristic composition and structure, assessed browse intensity, and compared stands of similar abiotic habitat but of different browsing regimes. Deer and livestock have significantly altered floristic composition and stand structure along this gradient. They impair tree regeneration and pose a long-term threat to the continued existence of a forest cover. Resumen: La presencia de ganado y ciervo introducido dentro del Parque Nacional Nahuel Huapi en el sudoeste de Argentina, representa un importante problema de manejo. Dado los beneficios economicos y sociales de la caza deportiva y la produccion ganadera, la erradicacion de estas especies introducidas es impracticable por razones politicas. Como alternativa de manejo, se intenta minimizar los efectos de estos animales evitando su dispersion hacia las areas mas pristinas del Parque y procurando disminuir sus densidades poblacionales. En el caso de la produccion ganadera tambien se intenta promover su reubicacion en sitios adecuados de la Reserva Nactional, donde se permite el desarrollo de actividades ganaderas. Es necesario por ello informacion detallada sobre el impacto de los herbivoros introducidos tanto para guiar el manejo en los diversos tipos de vegetacion del Parque, como para justificar medidas destinadas al control de animales exoticos dentro del Parque. Examinamos el efecto ecologico de animales introducidos a lo largo del gradiente de vegetacion desde los bosques lluviosos andinos hasta bosquetes abiertos y estepa patagonica. En 30 rodales se tomaron muestras de composicion floristica y estructura, se estimo la intensidad de pastoreo y se compararon sitios abioticamente similares pero con diferentes regimenes de pastoreo. La presencia de ciervo y ganado ha alterado significativamente la composicion floristica y la estructura de rodales a lo largo del gradiente y reducido severamente la regeneracion de especies arboreas, representando a largo plazo una amenaza para la existencia de la cobertura boscosa.

Geometrical Factors and Metapopulation Dynamics of the Bush Cricket, Metrioptera bicolor Philippi (Orthoptera: Tettigoniidae)

Abstract: This paper presents a metapopulation study of the bush cricket, Metrioptera bicolor, living in a recently fragmented landscape The species inhabits grass and heathland patches of varying area and isolation Analyses are made of how these geometrical factors affect local population size and density, distribution pattern, and the probability of local extinction and colonization The proportion of available patches occupied varied between 72 and 79% during 1985–1990 Unoccupied patches were smaller and more isolated than those that were occupied Patches where populations became extinct during this period were smaller than those with persisting populations Since local population size was well correlated with patch area, it was clear that stochastic extinctions only occurred in small populations Critical patch size for population extinction was approximately half a hectare Colonized patches were less isolated than those that had not been colonized Critical inter-patch distance for colonization was about 100 meters The turnover was restricted to an identifiable share of the available patches Only 33% of the patches were so small that extinction due to stochastic causes could be considered highly probable This metapopulation will therefore most likely persist over a considerable period in its present spatial structure There are apparent threats of further fragmentation, however, and nothing is known about the likelihood of large-scale extinctions resulting from extremely unfavorable weather conditions Nevertheless, our results show that it is appropriate to include geometrical factors in metapopulation models Este trabajo presenta un estudio metapoblacional del grillo Metrioptera bicolor que vive en un paisaje recientemente fragmentado Esta especie habita parches de pasto y matorrales cuyas superficies y grados de aislamiento varian Se analiza como estos factores geometricos afectan el tamano y densidad poblacional local, los patrones de distribucion y la probabilidad de extincion local y colonizacion La proporcion de parches disponibles que estaban ocupados oscilo entre un 72–79% durante el periodo 1985–1990 Los parches desocupados fueron mas pequenos y estaban mas aislados que aquellos que se encontraban ocupados Los parches donde las poblaciones se extinguieron durante este periodo fueron mas pequenos que aquellos con poblaciones que persistieron Dado que el tamano poblacional local estaba bien correlacionado con el area de los parches, fue evidente que extinciones estocasticas solo ocurrieron en poblaciones pequenas El tamano deparche critico para la extincion poblacional fue de aproximadamente media hectarea Los parches colonizodos estaban menos aislados que aquellos que no fueron colonizados La distancia critica entre patches para la colonizacion fue de aproximadamente 100 metros El recambio estuvo restringido a una porcion identificable de los parches disponibles Solo un 33% de los parches fueron lo suficientemente pequenos como para que la extincion debido a causas estocasticas pudiese ser considerada altamente probable Por consiguiente, es muy probable que esta metapoblacion persista con su estructura espacial actual durante unperiodo de tiempo considerable Sin embargo, existen claras amenazas de fragmentacion adicional y nada es sabido sobre la probabilidad de extinciones a gran escala, resultantes de condiciones climaticas extremadamente desfavorables De cualquier modo, nuestros resultados indican que es apropiado incluir factores geometricos en modelos metapoblacionales