Showing papers in "Conservation Biology in 2000"

Review of ecological effects of roads on terrestrial and aquatic communities.

Abstract: Roads are a widespread and increasing feature of most landscapes. We reviewed the scientific liter- ature on the ecological effects of roads and found support for the general conclusion that they are associated with negative effects on biotic integrity in both terrestrial and aquatic ecosystems. Roads of all kinds have seven general effects: mortality from road construction, mortality from collision with vehicles, modification of animal behavior, alteration of the physical environment, alteration of the chemical environment, spread of exotics, and increased use of areas by humans. Road construction kills sessile and slow-moving organisms, injures organisms adjacent to a road, and alters physical conditions beneath a road. Vehicle collisions affect the demography of many species, both vertebrates and invertebrates; mitigation measures to reduce roadkill have been only partly successful. Roads alter animal behavior by causing changes in home ranges, move- ment, reproductive success, escape response, and physiological state. Roads change soil density, temperature, soil water content, light levels, dust, surface waters, patterns of runoff, and sedimentation, as well as adding heavy metals (especially lead), salts, organic molecules, ozone, and nutrients to roadside environments. Roads promote the dispersal of exotic species by altering habitats, stressing native species, and providing movement corridors. Roads also promote increased hunting, fishing, passive harassment of animals, and landscape modifications. Not all species and ecosystems are equally affected by roads, but overall the pres- ence of roads is highly correlated with changes in species composition, population sizes, and hydrologic and geomorphic processes that shape aquatic and riparian systems. More experimental research is needed to com- plement post-hoc correlative studies. Our review underscores the importance to conservation of avoiding con- struction of new roads in roadless or sparsely roaded areas and of removal or restoration of existing roads to benefit both terrestrial and aquatic biota.

A survey and overview of habitat fragmentation experiments.

Abstract: Habitat destruction and fragmentation are the root causes of many conservation problems. We conducted a literature survey and canvassed the ecological community to identify experimental studies of terrestrial habitat fragmentation and to determine whether consistent themes were emerging from these studies. Our survey revealed 20 fragmentation experiments worldwide. Most studies focused on effects of fragmentation on species richness or on the abundance(s) ofparticular species. Other important themes were the effect offragmentation in interspecific interactions, the role of corridors and landscape connectivity in in- dividual movements and species richness, and the influences of edge effects on ecosystem services. Our com- parisons showed a remarkable lack of consistency in results across studies, especially with regard to species richness and abundance relative to fragment size. Experiments with arthropods showed the best fit with the- oretical expectations of greater species richness on larger fragments. Highly mobile taxa such as birds and mammals, early-successional plant species, long-lived species, and generalist predators did not respond in the "expected" manner. Reasons for these discrepancies included edge effects, competitive release in the habitat fragments, and the spati.al scale of the experiments. One of the more consistently supported hypotheses was that movement and species richness are positively affected by corridors and connectivity, respectively. Tran- sient effects dominated many systems;,for example, crowding of individuals on fragments commonly was ob- served afterfragmentation, followed by a relaxation toward lower abundance in subsequentyears. The three long-term studies (?14 years) revealed strong patterns that would have been missed in short-term investiga- tions. Our results emphasize the wide range of species-specific responses to fragmentation, the need for eluci- dation of behavioral mechanisms affecting these responses, and the potentialfor changing responses to frag- mentation over time.

Indicators of biodiversity for ecologically sustainable forest management

Abstract: The conservation of biological diversity has become one of the important goals of managing for- ests in an ecologically sustainable way. Ecologists and forest resource managers need measures to judge the success or failure of management regimes designed to sustain biological diversity. The relationships between potential indicator species and total biodiversity are not well established. Carefully designed studies are re- quired to test relationships between the presence and abundance of potential indicator species and other taxa and the maintenance of critical ecosystem processes in forests. Other indicators of biological diversity in forests, in addition or as alternatives to indicator species, include what we call structure-based indicators. These are stand-level and landscape-level (spatial) features of forests such as stand structural complexity and plant species composition, connectivity, and heterogeneity. Although the adoption of practices to sustain (or recreate) key characteristics of forest ecosystems appear intuitively sensible and broadly consistent with cur- rent knowledge, information is lacking to determine whether such stand- and landscape-level features of for- ests will serve as successful indices of (and help conserve) biodiversity. Given our limited knowledge of both indicator species and structure-based indicators, we advocate the following four approaches to enhance biodiversity conservation in forests: (1) establish biodiversity priority areas (e.g., reserves) managed prima- rily for the conservation of biological diversity; (2) within production forests, apply structure-based indica- tors including structural complexity, connectivity, and heterogeneity; (3) using multiple conservation strate- gies at multiple spatial scales, spread out risk in wood production forests; and (4) adopt an adaptive management approach to test the validity of structure-based indices of biological diversity by treating man- agement practices as experiments. These approaches would aim to provide new knowledge to managers and improve the effectiveness of current management strategies.

Estimate of the Area Affected Ecologically by the Road System in the United States

Abstract: In view of an extensive road system, abundant and rapidly growing vehicular traffic, and a scattered literature indicating that some ecological effects of roads extend outward for >100 m, it seems likely that the cumulative ecological effect of the road system in the United States is considerable. Two recent studies in The Netherlands and Massachusetts ( U.S.A.) evaluated several ecological effects of roads, including traffic noise effects, and provide quantitative evidence for a definable "road-effect zone." Based on the approximate width of this asymmetric convoluted zone, I estimate that about one-fifth of the U.S. land area is directly affected ecologically by the system of public roads. I identify a series of assumptions and variables suggesting that over time this preliminary estimate is more likely to rise than drop. Several transportation planning and policy recommendations, ranging from perforating the road barrier for wildlife crossings to closing certain roads, offer promise for reducing this enormous ecological effect.

The ecological road-effect zone of a massachusetts (u.s.a.) suburban highway

Abstract: Ecological flows and biological diversity trace broad patterns across the landscape, whereas transportation planning for human mobility traditionally focuses on a narrow strip close to a road or highway. To help close this gap we examined the "road-effect zone" over which significant ecological effects extend outward from a road. Nine ecological factors2014involving wetlands, streams, road salt, exotic plants, moose, deer, amphibians, forest birds, and grassland birds2014were measured or estimated near 25 km of a busy four-lane highway west of Boston, Massachusetts. The effects of all factors extended >100 m from the road, and moose corridors, road avoidance by grassland birds, and perhaps road salt in a shallow reservoir extended outwards >1 km. Most factors had effects at 220135 specific locations, whereas traffic noise apparently exerted effects along most of the road length. Creating a map of these effects indicates that the road-effect zone averages approximately 600 m in width and is asymmetric, with convoluted boundaries and a few long fingers. We conclude that busy roads and nature reserves should be well separated, and that future transportation systems across landscapes can provide for ecological flows and biological diversity in addition to safe and efficient human mobility.

Biodiversity and disease risk : The case of Lyme disease

Abstract: Utilitarian arguments concerning the value of biodiversity often include the benefits of animals, plants, and microbes as sources of medicines and as laboratory models of disease. The concept that species di- versity per se may influence risk of exposure to disease has not been well developed, however. We present a conceptual model of how high species richness and evenness in communities of terrestrial vertebrates may re- duce risk of exposure to Lyme disease, a spirochetal ( Borrelia burgdorferi ) disease transmitted by ixodid tick vectors. Many ticks never become infected because some hosts are highly inefficient at transmitting spirochete infections to feeding ticks. In North America, the most competent reservoir host for the Lyme disease agent is the white-footed mouse ( Peromyscus leucopus ), a species that is widespread and locally abundant. We suggest that increases in species diversity within host communities may dilute the power of white-footed mice to in- fect ticks by causing more ticks to feed on inefficient disease reservoirs. High species diversity therefore is ex- pected to result in lower prevalence of infection in ticks and consequently in lower risk of human exposure to Lyme disease. Analyses of states and multistate regions along the east coast of the United States demonstrated significant negative correlations between species richness of terrestrial small mammals (orders Rodentia, In- sectivora, and Lagomorpha), a key group of hosts for ticks, and per capita numbers of reported Lyme disease cases, which supports our " dilution effect " hypothesis. We contrasted these findings to what might be expected when vectors acquire disease agents efficiently from many hosts, in which case infection prevalence of ticks may increase with increasing diversity hosts. A positive correlation between per capita Lyme disease cases and species richness of ground-dwelling birds supported this hypothesis, which we call the " rescue effect ." The reservoir competence of hosts within vertebrate communities and the degree of specialization by ticks on par- ticular hosts will strongly influence the relationship between species diversity and the risk of exposure to the many vector-borne diseases that plague humans.

Wetland Loss and Biodiversity Conservation

Abstract: Most species of wetland-dependent organisms live in multiple local populations sustained through occasional migration. Retention of minimum wetland densities in human-dominated landscapes is fundamental to conserving these organisms. An analysis of wetland mosaics was performed for two regions of the northeastern United States to assess the degree to which historical wetland loss alters the metrics of wetland mosaics and to assess potential future effects mediated by differently structured wetland regulations. These analyses indicated that profound reductions in wetland density and proximity are associated with increased human populations and that protections for all wetlands >1 acre (0.4 ha) are likely required to retain wetland densities minimally sufficient to sustain the wetland biota.

Effects of Subsistence Hunting on Vertebrate Community Structure in Amazonian Forests

Abstract: Subsistence hunting affects vast tracts of tropical wilderness that otherwise remain structurally unal- tered, yet distinguishing hunted from nonhunted tropical forests presents a difficult problem because this diffuse form of resource extraction leaves few visible signs of its occurrence. I used a standardized series of line-transect censuses conducted over a 10-year period to examine the effects of subsistence game harvest on the structure of vertebrate communities in 25 Amazonian forest sites subjected to varying levels of hunting pressure. Crude verte- brate biomass, which was highly correlated with hunting pressure, gradually declined from nearly 1200 kg km 2 2 at nonhunted sites to less than 200 kg km 2 2 at heavily hunted sites. Hunting had a negative effect on the total biomass and relative abundance of vertebrate species in different size classes at these forest sites, but it did not af- fect their overall density. In particular, persistent hunting markedly reduced the density of large-bodied game spe- cies ( . 5 kg), which contributed a large proportion of the overall community biomass at nonhunted sites (65- 78%) and lightly hunted sites (55-71%). Nutrient-rich floodplain forests contained a consistently greater game biomass than nutrient-poor unflooded forests, once I controlled for the effects of hunting pressure. Conservative estimates of game yields indicate that as many as 23.5 million game vertebrates, equivalent to 89,224 tons of bushmeat with a market value of US$190.7 million, are consumed each year by the rural population of Brazil- ian Amazonia, which illustrates the enormous socioeconomic value of game resources in the region. My cross- site comparison documents the staggering effect of subsistence hunters on tropical forest vertebrate communities and highlights the importance of considering forest types and forest productivity in game management pro- grams.

Bat Diversity and Abundance as Indicators of Disturbance in Neotropical Rainforests

Abstract: Evaluating the degree of disturbance of any region to determine its relative importance for conservation purposes requires procedures that are relatively inexpensive and that yield accurate results fast. Because bats are abundant, diverse, and easy to sample, especially in the Neotropical rainforest, they fulfill several of the requirements of indicator species as identified in the literature. For 10 months we sampled bat communities in the Selva Lacandona in Chiapas, Mexico, at 15 sites representing five habitats. We also measured 10 variables representing vegetation structure and diversity at each site. With fuzzy-set techniques we produced a gradient classification of disturbance for the 15 sites based on the vegetation data. We explored the relationship between vegetation conditions, described as the membership degrees in the construct “fuzzy forest set” (the complementary fuzzy set of “disturbance”), and four bat community variables. Bat species richness, number of rare bat species, and the bat diversity index were positively correlated with the vegetation scores, and relative abundance of the most abundant bat species was negatively correlated with vegetation scores. A high number of phyllostomine species in a community is a good indicator of low levels of disturbance. Although a single indicator group will probably not be sufficient for decision-making processes in conservation, evaluating bat populations may be a good first step in assessing an area's conservation value, especially in rainforest regions.

Training Captive‐Bred or Translocated Animals to Avoid Predators

Abstract: Animal reintroductions and translocations are potentially important interventions to save species from extinction, but most are unsuccessful. Mortality due to predation is a principal cause of failure. Animals that have been isolated from predators, either throughout their lifetime or over evolutionary time, may no longer express appropriate antipredator behavior. For this reason, conservation biologists are beginning to include antipredator training in pre-release preparation procedures. We describe the evolutionary and ontogenetic circumstances under which antipredator behavior may degenerate or be lost, and we use principles from learning theory to predict which elements can be enhanced or recovered by training. The empirical literature demonstrates that training can improve antipredator skills, but the effectiveness of such interventions is influenced by a number of constraints. We predict that it will be easier to teach animals to cope with predators if they have experienced ontogenetic isolation than if they have undergone evolutionary isolation. Similarly, animals should learn more easily if they have been evolutionarily isolated from some rather than all predators. Training to a novel predator may be more successful if a species has effective responses to similar predators. In contrast, it may be difficult to teach proper avoidance behavior, or to introduce specialized predator-specific responses, if appropriate motor patterns are not already present. We conclude that pre-release training has the potential to enhance the expression of preexisting antipredator behavior. Potential training techniques involve classical conditioning procedures in which animals learn that model predators are predictors of aversive events. However, wildlife managers should be aware that problems, such as the emergence of inappropriate responses, may arise during such training.

Role of Light Availability and Dispersal in Exotic Plant Invasion along Roads and Streams in the H. J. Andrews Experimental Forest, Oregon

Abstract: We examined the roles of dispersal mechanism, a biological barrier; light availability, an environ- mental barrier; and level of disturbance, a physical barrier, in explaining the spatial patterns of exotic plant species along road and stream segments in a forest landscape in the western Cascade Range of Oregon (U.S.A). The presence or absence of 21 selected exotic plant species and light levels were observed along 0.3- to 1.0-km transects within four habitat types. Each habitat represented a different level of disturbance: high-use roads, low-use roads, abandoned roads, and streams in the H. J. Andrews Experimental Forest. Nearly 300 50 3 2-m sampling units were surveyed along five transects in each habitat type. We used ordination (nonmetric multidimensional scaling) and logistic regression to analyze data. All of the nearly 200 sampling units along roads with high and low levels of vehicle traffic contained at least one exotic plant species, and some con- tained as many as 14. Streams that were most recently disturbed by floods 20-30 years ago and abandoned spur roads with no traffic for 20-40 years also had numerous exotic species. Roads and streams apparently serve multiple functions that enhance exotic species invasion in this landscape: they act as corridors or agents for dispersal, provide suitable habitat, and contain reservoirs of propagules for future episodes of in- vasion. Species-specific dispersal mechanisms, habitat characteristics, and disturbance history each explain some, but not all, of the patterns of exotic species invasion observed in this study.

Fishery Stability, Local Extinctions, and Shifts in Community Structure in Skates

Abstract: Skates are arguably the most vulnerable of exploited marine fishes. Their vutlnerability is often as- sessed by examiningfisheries catch trends, but these data are not generally recorded on a species basis except in France. Aggregated skate catch statistics tend to exhibit more stable trends than those of other elasnmo- branch fisheries. We tested whether such apparent stability in aggregated catch trends could mask population declines of individual species. We examined two time series of species-specific surveys of a relatively stable skate fishery in the northeast Atlantic. These surveys revealed the disappearance of two skate species, long- nose skate (Dipturus oxyrhinchus) and white skate (Rostroraja alba) and confirmed a previously documented decline of the common skate (D. batis). Of the remaining five skate species, the three larger ones have de- clined, whereas twvo smaller species have increased in abundance. The increase in abundance and biomass of the smaller species has resulted in the stability of the aggregated catch trends. Becatuse there is significant di- etary overlap among species, we suiggest the increase in abundance of the smaller species ma) be due to com-

Factors Influencing the Effectiveness of Wildlife Underpasses in Banff National Park, Alberta, Canada

Abstract: Wildlife crossing structures are intended to increase permeability and habitat connectivity across roads. Few studies, however, have assessed the effectiveness of these mitigation measures in a multispecies or community level context. We used a null model to test whether wildlife crossing structures serve large mam- mal species equally or whether such structures limit habitat connectivity across roads in species-specific ways. We also modeled species responses to 14 variables related to underpass structure, landscape features, and hu- man activity. Species performance ratios (observed crossing frequency to expected crossing frequency) were evaluated for four large carnivore and three ungulate species in 11 underpass structures in Banff National Park, Alberta, Canada. Observed crossing frequencies were collected in 35 months of underpass monitoring. Expected frequencies were developed from three independent models: radio telemetry, pellet counts, and hab- itat-suitability indices. The null model showed that species responded to underpasses differently. In the pres- ence of human activity carnivores were less likely to use underpasses than were ungulates. Apart from hu- man activity, carnivore performance ratios were better correlated to landscape variables, and ungulate performance ratios were better correlated to structural variables. We suggest that future underpasses de- signed around topography, habitat quality, and location will be minimally successful if human activity is not managed.

Effects of Roads on Hydrology, Geomorphology, and Disturbance Patches in Stream Networks

Abstract: We outline a view of how road networks interact with stream networks at the landscape scale and, based on examples from recent and current research, illustrate how these interactions might affect biological and ecological processes in stream and riparian systems. At the landscape scale, certain definable geometric interactions involving peak flows ( floods) and debris flows (rapid movements of soil, sediment, and large wood down steep stream channels) are influenced by the arrangement of the road network relative to the stream network. Although disturbance patches are created by peak-flow and debris-flow disturbances in mountain landscapes without roads, roads can alter the landscape distributions of the starting and stopping points of debris flows, and they can alter the balance between the intensity of flood peaks and the stream net- work's resistance to change. We examined this conceptual model of interactions between road networks and stream networks based on observations from a number of studies in the H. J. Andrews Experimental Forest, Oregon (U.S.A.). Road networks appear to affect floods and debris flows and thus modify disturbance patch dynamics in stream and riparian networks in mountain landscapes. We speculate that these changes may in- fluence the rates and patterns of survival and recovery of disturbed patches in stream networks, affecting ec- osystem resilience, and we outline an approach for detecting such effects based on a patch dynamics perspec- tive. A field sampling scheme for detecting the magnitude of various road effects on stream and riparian ecology could involve (1) landscape stratification of inherent stream network susceptibility to floods or de- bris flows, (2) overlay of road and stream networks and creation of areas with various densities of road- stream crossings, emphasizing midslope road-stream crossings, and (3) designations of expected high- and low-impact stream segments based on numbers of upstream road-stream crossings where sampling of se- lected biological variables would be conducted.

Roads, Development, and Conservation in the Congo Basin

Abstract: Road density is closely linked to market accessibility, economic growth, natural resource exploitation, habitat fragmentation, deforestation, and the disappearance of wildlands and wildlife. Research in the Republic of Congo shows that roads established and maintained by logging concessions intensify bushmeat hunting by providing hunters greater access to relatively unexploited populations of forest wildlife and by lowering hunters' costs to transport bushmeat to market. Reconciling the contrary effects of roads on economic development and biodiversity conservation is one of the key challenges to wildlife managers in all nations. As the Democratic Republic of Congo prepares to reconstruct its almost completely collapsed road system, the government, donors, and conservation organizations have a unique opportunity to strategically prioritize investment in segments of the network that would maximize local and national economic benefits while minimizing adverse effects on forest wildlife. Resumen: La densidad de carreteras esta estrechamente ligada al acceso a mercados, el crecimiento economico, la explotacion de recursos naturales, la fragmentacion del habitat, la deforestacion y la desaparicion de tierras y vida silvestre. Investigacion en la Republica del Congo muestra que las carreteras establecidas y mantenidas por las concesiones para tala de arboles intensifican la caceria al proveer a los cazadores un mayor acceso a poblaciones forestales de vida silvestre relativamente sin explotar y al disminuir el costo de transporte de la carne obtenida por la caza hacia el mercado. La reconciliacion de los efectos contrarios de las carreteras en el desarrollo economico y la conservacion de la biodiversidad es uno de los retos clave para los manejadores de vida silvestre en todas las naciones. A medida que la Republica Democratica del Congo se prepara para reconstruir su casi completamente colapsado sistema carretero, el gobierno, los donadores y las organizaciones no gubernamentales conservacionistas tienen una oportunidad unica para priorizar estrategicamente las inversiones en segmentos de la red carretera que podrian maximizar los beneficios economicos locales y nacionales al mismo tiempo que se minimicen los impactos adversos sobre la vida silvestre forestal.

Relationships among Isolated Wetland Size, Hydroperiod, and Amphibian Species Richness: Implications for Wetland Regulations

Abstract: Wetland development within the United States is regulated primarily by size. Decisions concerning wetland destruction or conservation are therefore based in part on three inherent assumptions: (1) small wetlands contain water for short portions of the year; (2) small wetlands support few species; and (3) species found in small wetlands are also found in larger wetlands. We tested these assumptions using data on wetland size, relative hydroperiod (drying scores), and relative species richness of amphibians in depression wetlands of the southeastern United States. We found a significant (p = 0.03) but weak (r2 = 0.05) relationship between hydroperiod and wetland size and no relationship (p = 0.48) between amphibian species richness and wetland size. Furthermore, synthetic models of lentic communities predict that short-hydroperiod wetlands support a unique group of species. Empirical investigations support this prediction. Our results indicate that hydroperiod length should be included as a primary criterion in wetland regulations. We advocate a landscape approach to wetlands regulation, focused in part on conserving a diversity of wetlands that represent the entire hydroperiod gradient. Resumen: El desarrollo de humedales dentro de los Estados Unidos es regulado principalmente por el tamano. Por lo tanto, las decisiones referentes a la destruccion o conservacion de humedales se basan, en parte, en tres conjeturas inherentes: (1) los humedales pequenos contienen agua durante periodos cortos del ano, (2) los humedales pequenos sostienen pocas especies, y (3) las especies encontradas en humedales pequenos se encuentran tambien en los humedales grandes. Evaluamos estas conjeturas utilizando datos de tamano, hidroperiodo relativo (valores de seca) y riqueza relativa de especies de anfibios en humedales de depresion del sudeste de los Estados Unidos. Encontramos una relacion significativa (p = 0.03) pero debil (r2 = 0.05) entre el hidroperiodo y el tamano del humedal y ninguna relacion (p = 0.48) entre la riqueza de especies de anfibios y el tamano del humedal. Mas aun, modelos sintetizados de comunidades lenticas predicen que los humedales con hidroperiodos cortos sostienen a un grupo de anfibios unico. Las investigaciones empiricas apoyan esta prediccion. Nuestros resultados indican que la longitud del hidroperiodo deberia ser incluido como un criterio primario en las regulaciones de humedales. Abogamos por una aproximacion de paisaje para la regulacion de humedales, enfocada en parte en la conservacion de la diversidad de humedales que representen el gradiente de hidroperiodo completo.

Bat- and Bird-Generated Seed Rains at Isolated Trees in Pastures in a Tropical Rainforest

Abstract: Bats are abundant and effective seed dispersers inside the forest, but what happens when a forest is fragmented and transformed into pasture? The landscape at Los Tuxtlas, Mexico, originally rainforest, is greatly fragmented and covered with pastures. We analyzed the seed rains produced by frugivorous bats and birds under isolated trees in pastures in the fragmented landscape and the contribution of this process to vegetational recovery. We surveyed bats and obtained fecal samples under isolated trees in pastures. We also collected seed rain below the canopy of 10 isolated Ficus trees, separating nocturnally dispersed seeds from diurnally dispersed seeds. We caught 652 bats of 20 species; 83% of captures were frugivores. The most abundant species were Sturnira lilium (48%), Artibeus jamaicensis (18%), Carollia perspicillata (12%), and Dermanura tolteca (11%). Fecal samples contained seeds of 19 species in several families: Piperaceae (50%), Moraceae (25%), Solanaceae (12%), Cecropiaceae (10%), and others (3%). Sturnira lilium was the most important disperser bat in pastures. Seed rain was dominated by zoochorous species (89%). We found seed diversity between day and night seed captures to be comparable, but we found a significant interaction of disperser type ( bird or bat) with season. Seven plant species accounted for 79% of the seed rain: Piper auritum (23%), Ficus ( hemiepiphytic-strangler tree) spp. (17%), Cecropia obtusifolia (10%), P. amalago (10%), Ficus ( free-standing tree) spp. (8%), P. yzabalanum (6%), and Solanum rudepanum (5%). Bats and birds are important seed dispersers in pastures because they disperse seeds of pioneer and primary species (trees, shrubs, herbs, and epiphytes), connect forest fragments, and maintain plant diversity. Consequently, they might contribute to the recovery of woody vegetation in disturbed areas in tropical humid forests. Resumen: Los murcielagos son abundantes y efectivos dispersores de semillas en la selva humeda alta. Pero, ?que sucede cuando la selva es fragmentada y convertida en pastizales? El paisaje en Los Tuxtlas, Mexico, cuya vegetacion original era la de bosque lluvioso, esta fuertemente fragmentado y dominado por pastizales. Analizamos la lluvia de semillas producida por murcielagos y aves frugivoras bajo arboles aislados en pastizales del paisaje fragmentado, y la contribucion de este proceso a la recuperacion de la vegetacion. Capturamos murcielagos y obtuvimos muestras fecales bajo arboles aislados en pastizales. Colectamos la lluvia de semillas bajo 10 Ficus aislados, separando las semillas “nocturnas” de las “diurnas.” Capturamos 652 murcielagos de 20 especies, el 83% de ellos fueron frugivoros. Las especies dominantes fueron: Sturnira lilium (48%), Artibeus jamaicensis (18%), Carollia perspicillata (12%), y Dermanura tolteca (11%). Las muestras fecales contenian semillas de 19 especies de varias familias: Piperaceae (50%), Moraceae (25%), Solanacea (12%), Cecropiaceae (10%), y otras (3%). Sturnira lilium resulto ser el murcielago dispersor mas importante del pastizal. En la lluvia de semillas el 89% de las especies fueron zoocoras. No se encontro diferencia en la diversidad de semillas depositadas en la noche o en el dia; sin embargo, hubo una interaccion significativa del tipo de dispersor (ave o murcielago) con la epoca del ano. Siete especies dominaron el 79% del total de la lluvia: Piper auritum (23%), Ficus ( hemiepifito-matapalo; 17%), Cecropia obtusifolia (10%), P. amalago (10%), Ficus (terrestre; 8%), P. yzabalanum (6%) y Solanum rudepanum (5%). Los murcielagos y las aves son importantes dispersores en pastizales ya que dispersan semillas de especies pioneras y primarias (arboles, arbustos, hierbas y epifitas); conectan remanentes de selva y mantienen la diversidad vegetal. Consecuentemente pueden promover la recuperacion de la vegetacion lenosa en areas perturbadas de regiones tropicales humedas.

Non‐Native Fish Introductions and the Decline of the Mountain Yellow‐Legged Frog from within Protected Areas

Abstract: One of the most puzzling aspects of the worldwide decline of amphibians is their disappearance from within protected areas. Because these areas are ostensib ly undisturbed, habitat alterations are generally perceived as unlikely causes. The introduction of non-native fishes into protected areas,however, is a common practice throughout the world and may exert an important influence on amphibian distributions. We quantified the role of introduced fishes (several species of trout) in the decline of the mountain yello w-legged-frog (Rana muscosa) in California's Sier ra Nevada through surveys of >1700 sites in two adjacent and historically fishless protected areas that dif fered primarily in the distribution of introduced fish. Negat ive effects of fishes on the distri bution of frogs we re evident at three spatial scales. At the l a n d s c ape scale, c o m p a risons between The two protected areas indicated that fish distri bution was stro n g ly n egat ive ly corre l at e d with the distribution of frogs. At the watershed scale, the percentage of total water-body surface area occupied by fishes was a highly significant predictor of the percenta ge of total water-body surface area occupied by fr ogs. At the scale (if individual water bodies, frogs were three times more likely to be found and six times more abundant in fishless than in fish-containing water bodies, after habitat effects were accounted for. The strong effect of introduced fishes on mountain yello w-legged frogs appears to result from the unique life history of this amphibian whic h frequently restricts larvae to deeper water bodies, the same habitats into which fishes have most frequently been introduced. Because fish populations in at least some Sierra Ne vada lakes can be remo ved with minimal effort, our results suggest that the decline of the mountain yellow-legged frog might be relatively easy to reverse.

Rethinking Tropical Forest Conservation: Perils in Parks

Abstract: According to some conservationists, large, pristine, uninhabited parks are the defining criterion of success in conserving tropical forests. They argue that human residents in tropical forests inevitably deplete populations of large animals through hunting, which triggers a chain reaction of ecological events that greatly diminish the conservation value of these forests. Hence, they believe that removal of people from tropical forests is an essential step in the creation of successful parks and in the conservation of nature in the tropics. This approach can lead to undesirable consequences, however. Forest residents—and rural people generally—are potent political actors in tropical forest regions and an essential component of the environmental political constituencies that are necessary for the long-term conservation of tropical forests. In Amazonia and elsewhere, rural people are defending far bigger areas of tropical forest from unfettered deforestation and logging than are parks, thereby conserving the ecological services provided by these forests and the majority of their component plant and animal species. Moreover, the data are too sparse to judge the effects of forest peoples on populations of large forest animals. The establishment of pristine, tropical forest parks is an important conservation goal, but the exclusive pursuit of this goal undermines the broader objectives of conservation when it identifies forest residents and other rural people as the enemies of nature.

Poachers Alter Mammal Abundance, Seed Dispersal, and Seed Predation in a Neotropical Forest

Abstract: We evaluated the hypothesis that poachers reduce the abundance of herbivorous mammals, and that this, in turn, alters seed dispersal, seed predation, and seedling recruitment for two palms ( Attalea bu- tyraceae and Astrocaryum standleyanum ) in central Panama. Using physical evidence left by poachers and in- terviews with forest guards, we quantified poaching intensity for eight forest sites. We quantified mammal abundance using transect counts and small-mammal traps. Abundance was inversely related to poaching intensity for 9 of 11 mammal species (significantly so for 5 species), confirming the first component of the hy- pothesis. The outcome of interactions among seeds, mammals, and beetles also varied with poaching inten- sity. Nonvolant mammals were the only seed-dispersal agents, and rodents and beetles were the only seed predators. We quantified seed fate by examining the stony endocarps that encase the seeds of both palms. The large, durable endocarps were located easily on the forest floor and bear characteristic scars when a rodent or beetle eats the enclosed seed. The proportion of seeds dispersed away from beneath fruiting conspecifics was inversely related to poaching intensity, ranging from 85% to 99% at protected sites where mammals were abundant and from 3% to 40% at unprotected sites where poachers were most active. The proportion of dis- persed seeds destroyed by beetles was directly related to poaching intensity, ranging from 0% to 10% at pro- tected sites and from 30% to 50% at unprotected sites. The proportion of dispersed seeds destroyed by rodents was inversely related to poaching intensity, ranging from 85% to 99% at protected sites and from 4% to 50% at unprotected sites. Finally, seedling densities were directly related to poaching intensity. There was no single relationship between poaching intensity and the biotic interactions that determine seedling recruitment. The net effect of poaching on seedling recruitment can be determined only empirically. For these palms, seedling densities were directly related to poaching intensity.

Bird communities and habitat as ecological indicators of forest condition in regional monitoring.

Abstract: Ecological indicators for long-term monitoring programs are needed to detect and assess changing environmental conditions. We developed and tested community-level environmental indicators for monitor- ing forest bird populations and associated habitat. We surveyed 197 sampling plots in loblolly-shortleaf pine forests, spanning an area from Georgia to Virginia (U.S.A.) and representing a gradient in levels of anthropo- genic disturbance. Ninety of these plots were randomly selected from a sampling grid, permitting quantitative assessment of cumulative distribution functions for bird community and habitat parameters. Species were in- dependently classified into habitat assemblages indicating birds typical of disturbed habitat (e.g., shrubland, forest edge) and undisturbed habitat (mature forest). Relative abundances of these assemblages were used to form a bird community index—similar to the index of biotic integrity applied to aquatic systems—showing the effects of habitat disturbance on forest bird communities. Bird communities on the majority of the sample area (52-75%, 90% confidence interval) were dominated by disturbance-tolerant species. Sites dominated by mature-forest species were comparatively uncommon. Habitat assemblages appeared to be particularly useful tools for environmental monitoring; individual species abundance was positively correlated with assemblage species richness, and assemblage members showed consistent responses to variations in disturbance level. To a lesser extent, component species of nesting guilds showed this pattern of cohesive responses, but those of for- aging guilds did not. We also developed a habitat index based on habitat variables that predicted bird com- munity index values. Habitat and bird community indices were strongly correlated in an independent vali- dation dataset, suggesting that the habitat index can provide a reliable predictor of bird community status. The two indices may be used in combination, with the bird community index providing a direct measure of the status of the bird community and the habitat index providing a basis on which to separate changes in the bird community into local habitat effects versus other factors (e.g., landscape level effects, changes on winter- ing grounds).

Fragmentation of Landscape as a Cause for Genetic Subdivision in Bank Voles

Abstract: We studied the barrier effects of various roadways on the genetic subdivision of bank vole (Clethrionomys glareolus) populations. Allele frequencies, genetic variability, and genetic distances of natural populations were calculated based on polymorphism of seven microsatellite markers. We compared bank vole populations in control areas without such barriers with animals from both sides of a country road, a railway, and a highway. Using F and R statistics, we demonstrated significant population subdivision in bank vole populations separated by the highway, but not in populations on either side of the other roadways or in the control area. Correlations between geographic and genetic distances were revealed by an extended method based on a Mantel analysis. This allowed us to measure genetic barrier effects and express them as additional geographic distances. For instance, statistically significant differences in allele frequencies in all seven loci examined existed among populations in southern Germany and Switzerland, which are separated by the Rhine River and Lake Constance. The real geographic distance between bank vole populations in Konstanz and those in Lengwil, Switzerland, was 6 km. According to this analysis the genetic barrier effect of the Rhine could be defined as an additional distance of 7.7 km. This study shows for the first time that not only old geographic barriers but also more recent fragmentation of landscape by, for example, highways has an important effect on gene flow and the genetic substructuring of populations, which should be considered in future environmental impact assessments. Resumen: En este trabajo estudiamos los efectos de barrera de varias vias de comunicacion terrestre en la subdivision genetica en poblaciones de ratones de campo ( Clethrionomys glareolus). Las frecuencias de alelos, la variabilidad genetica y las distancias geneticas de poblaciones naturales fueron calculadas en base a polimorfismos de siete marcadores microsatelite. Comparamos las poblaciones de ratones de campo en areas de control sin las barreras mencionadas contra animales de ambos lados de una carretera rural, una via de ferrocarril y una autopista. Mediante el uso de estadisticas F y R, demostramos una subdivision poblacional significativa en poblaciones de ratones separados por la autopista, pero no entre poblaciones en ambos lados de las otras vias de comunicacion o en el area control. Un metodo extendido basado en un analisis Mantel revelo correlaciones entre las distancias geograficas y las distancias geneticas. Esto nos permitio medir los efectos de barreras geneticas y expresarlos como distancias geograficas adicionales. Por ejemplo, las diferencias estadisticamente significativas en las frecuencias de alelos en los siete locus examinados existieron en poblaciones al sur de Alemania y Suiza, las cuales estan separadas por el rio Rin y el lago Constance. La distancia geografica real entre las poblaciones de ratones en Constanz y aquellas en Lenwil, Suiza fue de 6 km. De acuerdo con este analisis el efecto de la barrera genetica del rio Rin podria ser definida como una distancia adicional de 7.7 km. Este estudio muestra por primera vez que no solo las barreras geograficas de antano sino tambien la fragmentacion mas reciente del paisaje como la ocasionada por autopistas, por ejemplo, tienen un efecto importante en el flujo de genes y la subestructuracion de poblaciones. Esto debe ser considerado en evaluaciones futuras de impacto ambiental.

Long-Term Effects of Logging on African Primate Communities: a 28-Year Comparison From Kibale National Park, Uganda

Abstract: If logging is to be compatible with primate conservation, primate populations must be expected to recover from the disturbance and eventually return to their former densities. Surveys conducted over 28 years were used to quantify the long-term effects of both low- and high-intensity selective logging on the den- sity of the five common primates in Kibale National Park, Uganda. The most dramatic exception to the expec- tation that primate populations will recover following logging was that group densities of Cercopithecus mitis and C. ascanius in the heavily logged area continued to decline decades after logging. Procolobus tephrosceles populations were recovering in the heavily logged areas, but the rate of increase appeared to be slow (0.005 groups/km 2 per year). Colobus guereza appeared to do well in some disturbed habitats and were found at higher group densities in the logged areas than in the unlogged area. There was no evidence of an increase in Lophocebus albigena group density in the heavily logged area since the time of logging, and there was a ten- dency for its population to be lower in heavily logged areas than in lightly logged areas. In contrast to the findings from the heavily logged area, none of the species were found at a lower group density in the lightly logged area than in the unlogged area, and group densities in this area were not changing at a statistically significant rate. The results of our study suggest that, in this region, low-intensity selective logging could be one component of conservation plans for primates; high-intensity logging, however, which is typical of most logging operations throughout Africa, is incompatible with primate conservation.

Response Time of Wetland Biodiversity to Road Construction on Adjacent Lands

Abstract: Road construction may result in significant loss of biodiversity at both local and regional scales due to restricted movement between populations, increased mortality, habitat fragmentation and edge effects, invasion by exotic species, or increased human access to wildlife habitats, all of which are expected to increase local extinction rates or decrease local recolonization rates. Species loss is unlikely to occur immediately, however. Rather, populations of susceptible species are expected to decline gradually after road construction, with local extinction occurring sometime later. We document lags in wetland biodiversity loss in response to road construction by fitting regression models that express species richness of different taxa ( birds, mammals, plants, and herptiles) as a function of both current and historical road densities on adjacent lands. The proportion of variation in herptile and bird richness explained by road densities increased significantly when past densities were substituted for more current densities in multiple regression models. Moreover, for vascular plants, birds, and herptiles, there were significant negative effects of historical road densities when the most current densities were controlled statistically. Our results provide evidence that the full effects of road construction on wetland biodiversity may be undetectable in some taxa for decades. Such lags in response to changes in anthropogenic stress have important implications for land-use planning and environmental impact assessment.

Bayesian Methods in Conservation Biology

Abstract: Bayesian statistical inference provides an alternate way to analyze data that is likely to be more appropriate to conservation biology problems than traditional statistical methods. I contrast Bayesian techniques with traditional hypothesis-testing techniques using examples applicable to conservation. I use a trend analysis of two hypothetical populations to illustrate how easy it is to understand Bayesian results, which are given in terms of probability. Bayesian trend analysis indicated that the two populations had very different chances of declining at biologically important rates. For example, the probability that the first population was declining faster than 5% per year was 0.00, compared to a probability of 0.86 for the second population. The Bayesian results appropriately identified which population was of greater conservation concern. The Bayesian results contrast with those obtained with traditional hypothesis testing. Hypothesis testing indicated that the first population, which the Bayesian analysis indicated had no chance of declining at >5% per year, was declining significantly because it was declining at a slow rate and the abundance estimates were precise. Despite the high probability that the second population was experiencing a serious decline, hypothesis testing failed to reject the null hypothesis of no decline because the abundance estimates were imprecise. Finally, I extended the trend analysis to illustrate Bayesian decision theory, which allows for choice between more than two decisions and allows explicit specification of the consequences of various errors. The Bayesian results again differed from the traditional results: the decision analysis led to the conclusion that the first population was declining slowly and the second population was declining rapidly. Resumen: Las inferencias de la estadistica Bayesiana proveen una forma alternativa de analizar datos que probablemente sea mas apropiada para la conservacion biologica que los metodos estadisticos tradicionales. Compare tecnicas Bayesianas con tecnicas tradicionales de prueba de hipotesis, mediante el uso de ejemplos aplicables a la conservacion. Utilice un analisis de tendencias de dos poblaciones hipoteticas para ilustrar lo facil que es entender los resultados Bayesianos, los cuales se obtienen en forma de probabilidades. El analisis Bayesiano de tendencias indico que las dos poblaciones tenian probabilidades muy diferentes de disminuir a tasas biologicamente importantes. Por ejemplo, la probabilidad de que la primera poblacion disminuyera mas de un 5% por ano fue de 0.0, comparada con una probabilidad de un 0.86 para la segunda poblacion. Los resultados Bayesianos identifican adecuadamente cual poblacion era la de mayor interes para conservar. Los resultados Bayesianos se contrastan con aquellos obtenidos mediante pruebas de hipotesis tradicionales. Las pruebas de hipotesis indicaron que la primera poblacion ( la cual fue indicada por las pruebas Bayesianas como teniendo una probabilidad de disminucion mayor al 5% por ano) disminuia significativamente debido a que la disminucion ocurria a una tasa muy baja y las estimaciones de abundancia eran precisas. A pesar de la alta probabilidad de que la segunda poblacion experimente una disminucion seria, la prueba de hipotesis fallo al rechazar la hipotesis nula de no-disminucion, debido a que las estimaciones de abundancia eran poco precisas. Extendi el analisis de tendencias para ilustrar la teoria de decision Bayesiana, la cual permite decidir entre mas de dos posibilidades y permite una especificacion explicita de las consecuencias de varios errores. Los resultados Bayesianos difirieron una vez mas de los resultados tradicionales: el analisis de decisiones condujo a la conclusion de que la primera poblacion disminuia despacio y la segunda disminuia rapidamente.

Making Consistent IUCN Classifications under Uncertainty

Abstract: The World Conservation Union (IUCN) defined a set of categories for conservation status supported by decision rules based on thresholds of parameters such as distributional range, population size, population history, and risk of extinction. These rules have received international acceptance and have become one of the most important decision tools in conservation biology because of their wide applicability, objectivity, and simplicity of use. The input data for these rules are often estimated with considerable uncertainty due to measurement error, natural variation, and vagueness in definitions of parameters used in the rules. Currently, no specific guidelines exist for dealing with uncertainty. Interpretation of uncertain data by different assessors may lead to inconsistent classifications because attitudes toward uncertainty and risk may have an important influence on the classification of threatened species. We propose a method of dealing with uncertainty that can be applied to the current IUCN criteria without altering the rules, thresholds, or intent of these criteria. Our method propagates the uncertainty in the input parameters and assigns the evaluated species either to a single category (as the current criteria do) or to a range of plausible categories, depending on the nature and extent of uncertainties. Resumen: La Union Mundial para la Conservacion (IUCN) definio un grupo de categorias referentes a estados de conservacion sustentadas en reglas de decision basadas en umbrales de parametros como son el rango de distribucion, el tamano poblacional, la historia poblacional y el riesgo de extincion. Estas reglas han recibido aceptacion internacional y se han convertido en una de las herramientas mas importantes para la toma de decisiones en biologia de la conservacion debido a su amplia aplicabilidad, objetividad y simplicidad de uso. Los datos requeridos para estas reglas son frecuentemente estimados con una incertidumbre considerable debido a errores de medicion, variacion natural y vaguedad en la definicion de los parametros usados en las reglas. Actualmente no existen lineamientos especificos para enfrentar la incertidumbre. La interpretacion de datos inciertos por diferentes estimadores puede conducir a clasificaciones inconsistentes debido a que ciertas actitudes hacia la incertidumbre y el riesgo pueden tener una influencia importante en la clasificacion de especies amenazadas. Proponemos un metodo para enfrentar a la incertidumbre que puede ser aplicado a los criterios actuales de IUCN sin alterar las reglas, los umbrales, o la intencion de estos criterios. Nuestro metodo propaga la incertidumbre en los parametros usados y asigna a la especie evaluada a una sola categoria (a como lo hace el criterio actual) o a un rango de categorias plausibles, dependiendo de la naturaleza y la extension de las incertidumbres.

Extracting Humans from Nature

Abstract: Traditional and indigenous people can claim incontrovertible rights to their land. As morally responsible humans we must support their struggle. This responsibility does not mean that as conservationists we must count as conservation everything that these people have done and wish to do. As independent peoples with rights to selfdetermination, their future should be in their own handswhether that future meets our expectations or not. It is remarkable that we find ourselves making this obvious point to a group of experienced and savvy professionals who have spent considerable time in defense of indigenous and traditional peoples. We won't claim to tell Steve Schwartzman and his co-authors about the political virtues or shortcomings of rubber tappers and Amazonian Indians, because they are experts in such matters, insofar as outsiders can be. Nevertheless, speaking on behalf of those peoples as if their interests were identical with conservation, biodiversity, and parks is disingenuous. In taking such a tack, the authors enter a twisted labyrinth of reasoning, which we find tortuous and politically dangerous for both conservation and forest-dwelling peoples. First, we thought that in various ways we had already published conclusions similar to those in the paper by Schwartzman et al. (Redford & Stearman 1993; Redford & Mansour 1996; Sanderson & Bird 1998). But, to our major disappointment, the authors use this very literature to set up a straw man, claiming the existence of an extremist group practicing "preservationist absolutism" and advocating the perfect against the good. Then they demolish the straw man with a flourish, arriving at a conclusion that is eminently reasonable, if derived differently. Our concern is that they arrive at their major point by accusing potential allies rather than recruiting them. The more important fault with the paper lies in an incomplete reading of the current literature, leading to unnecessary and sometimes incorrect conclusions. This is best illustrated with the repeated claim that indigenous human impact is inconsequential for biodiversity, based on a weak reading of the literature on human hunting. Schwartzman et al. state that "We are unaware of rigorously documented cases of local extinction, or severe depletion, of large animals-or any other species-in indigenous or extractive reserves. Several studies suggest that, to the contrary, hunting by forest communities' even over the long term, has not had these effects and that, given adequate territory, it does not threaten game species." They cite three references for this claim, none of which can support their conclusion. Further, the mounting evidence in the literature strengthens the main vein of the literature, that in virtually all cases large game animals are strongly depleted where human population densities exceed one person per square kilometer (Robinson & Bennett 2000a). This conclusion is borne out in studies done in tropical forests of all types throughout the world, with lands of indigenous and traditional peoples offering no exception (Robinson & Bennett 2000b). More specific evidence comes from uncited work done in extractive reserves in Brazil-the same setting in which the authors claim there has been no effect and no available studies. Two studies document local extinction of several species of game animals in extractive reserves due to hunting by rubber tappers (Martins 1993; Calouro 1995). The study Schwartzman and his colleagues call for-comparing densities of game animals in extractive reserves and unhunted forests-has, in fact, been conducted (Martins 1993; Peres 2000; Robinson & Bennett 2000a), and the results demonstrate the overwhelming negative effect of human hunting. And these results come from an extractive reserve with a human population density of one person per square kilometer, a density much lower than that of most other extractive reserves (Martins 1993). The same results have been demonstrated on Indian lands in Central America (Ventocilla et al. 1996), Indian lands in the Amazon (Chase Smith 1996; Alvard 1994; Peres 2000), and in Amazonian mestizo territories (Bodmer et al. 1994). There is simply no doubt that human hunting causes dramatic local reduction in the density of game species and in some cases leads to local extinction. Peres (2000) concludes from an exhaustive study of the effects of hunting at 24 Amazonian sites, including extractive reserves and Indian lands that "Subsistence hunting in Amazonia . .. can result in profound changes in the structure of tropical forest vertebrate communities through (a) shifts in the relaPaper submitted February 23, 2000; revised manuscript accepted MaY 3, 2000.

Cougar Dispersal Patterns, Metapopulation Dynamics, and Conservation

Abstract: We examined cougar ( Puma concolor ) dispersal, emigration, and immigration in the San Andres Mountains, New Mexico, from 1985 to 1995 to quantify the effects of dispersal on the local population and surrounding subpopulations. We captured, tagged, and radio-collared animals to detect the arrival of new immigrants and dispersal characteristics of progeny. We found that cougars in southern New Mexico exhib- ited a metapopulation structure in which cougar subpopulations were separated by expanses of noncougar habitat and linked by dispersers. Of 43 progeny ( n 5 20 males, 23 females) studied after independence, only 13 females exhibited philopatric behavior. Males dispersed significantly farther than females, were more likely to traverse large expanses of noncougar habitat, and were probably most responsible for nuclear gene flow between habitat patches. We estimated that an average of 8.5 progeny (i.e., cougars born in the study area) successfully emigrated from and 4.3 cougars successfully immigrated to the San Andres Mountains each year. Concurrently, an average of 4.1 progeny were recruited into the San Andres cougar population. Pro- tected cougar subpopulations can contribute to metapopulation persistence by supplying immigrants to sur- rounding subpopulations that are affected by fragmentation or offtake by humans. Cougar population dy- namics and dispersal behavior dictate that cougar management and conservation should be considered on a regional scale.

Functional Equivalency between Rice Fields and Seminatural Wetland Habitats

Abstract: Evaluating the potential for anthropogenic habitats to act as surrogates for the natural habitats they replace is a key issue in conservation biology. In California, flooded rice fields are used by numerous aquatic birds during winter. If this habitat functions similarly to more natural wetlands, increased flooding may help replace the extensive wetlands that occurred in the region prior to agricultural development. I tested whether food abundance, perceived predation threat, foraging performance, and the way in which birds allocate their time to different behaviors differed between flooded rice fields and seminatural wetlands for several species of aquatic bird. When appropriate, I also compared flooded and unflooded fields. Invertebrate densities did not differ among habitats. Seminatural wetlands had less rice grain but more seeds from other plants than the two rice habitats. The frequency with which predators passed over a feeding area was lower in flooded fields than in unflooded fields or seminatural wetlands. Most differences in feeding performance and time allocation among habitats were small and statistically insignificant. For some species, feeding efficiency was greater in seminatural wetlands than in flooded fields. Increasing attack rates and the amount of time spent feeding when in flooded fields, however, may allow birds to compensate for reduced efficiency. Multivariate analyses showed that group size, predation threat, time of day, date, and water depth often were associated with behaviors, but that these variables rarely accounted for habitat differences. Flooded fields apparently provide equivalent foraging habitat to seminatural wetlands and, because of reduced predation threat, may be a safer habitat for waterbirds. Thus, if managed appropriately, one of the world's dominant forms of agriculture can provide valuable waterbird habitat. Resumen: La evaluacion del potencial en habitats antropogenicos para actuar como substitutos de los habitats naturales que remplazaron es un tema clave en la biologia de la conservacion. En California, tierras inundadas para cultivo de arroz son utilizadas por numerosas aves acuaticas durante el invierno. Si estos habitats funcionan en forma similar a humedales mas naturales, el incremento de inundaciones podria ayudar a reemplazar los extensos humedales que existieron en la region antes del desarrollo agricultural. Analize si la abundancia de alimento, la percepcion del peligro de depredacion, el rendimiento en forrajeo y la forma en que las aves distribuyen su tiempo hacia diferentes conductas difieren entre arrozales inundados y humedales seminaturales para diferentes especies de aves acuaticas. Cuando fue posible, tambien compare arrozales inundados contra no inundados. Las densidades de invertebrados no difirieron entre habitats. Los humedales seminaturales tuvieron menos grano de arroz, pero mas semillas de otras plantas que los dos tipos de habitats de arrozal. La frecuencia con la que los depredadores pasaron sobre un area de alimentacion fue menor en los campos inundados que en los campos no inundados o los humedales seminaturales. La mayoria de las diferencias en el rendimiento alimenticio y el tiempo dedicado entre habitats fue pequeno y estadisticamente insignificante. Para algunas especies, la eficiencia alimenticia fue mayor en humedales seminaturales que en los campos inundados. Sin embargo, el incremento en las tasas de ataque y las cantidades de tiempo utilizado para alimentacion cuando los campos estaban inundados podria permitir a las aves compensar por esta reducida eficiencia. Un analisis multivariado mostro que el tamano de grupo, el peligro de depredacion, hora del dia, fecha y profundidad del agua estuvieron frecuentemente asociados con conductas, pero estas variables raramente aportaron elementos para encontrar diferencias entre habitats. Los arrozales inundados aparentemente proveen un habitat de forrajeo equivalente a los humedales seminaturales y debido a la reducida amenaza de depredacion, podrian ser un habitat seguro para aves acuaticas. Por lo tanto, si son manejados adecuadamente, una de las formas mas dominantes de agricultura a nivel mundial puede proporcionar habitat valioso para las aves acuaticas.