Showing papers on "Species richness published in 1989"

The Latitudinal Gradient in Geographical Range: How so Many Species Coexist in the Tropics

Abstract: The latitudinal gradient in species richness is paralleled by a latitudinal gradient in geographical-range size called Rapoport's rule. It is suggested that the greater annual range of climatic con...

Species-Area Relationship for Stream Fishes

Abstract: We sampled riffle and pool habitats of small streams in Minnesota, Illinois, and Panama to examine variation in species-area relationships within and between the respective fish faunas. For six of the seven steams studied, habitat volume was a better predictor of species richness than was habitat area, and number of individuals was a better predictor of species richness than habitat volume. Slopes of species-volume relationships were similar among regions, but the number of species per unit volume was greater in Panama. Multiple regression analyses indicated that knowledge of habitat complexity and volume did not enhance appreciably the capability of linear models to predict species richness from number of individuals in the sample. These results support the hypothesis that species-area relationships may often be epiphenomena stemming from the more com- prehensive community "samples" intercepted by larger habitat patches. Although number of individuals was the best single predictor of species richness, habitat structure and type clearly influenced species' distributions in some streams, thereby indicating that species- area relationships were not strictly sampling phenomena. An index of habitat complexity based on depth, current, and bottom type was correlated with species richness in two Panama streams. Also, the abundance of individual species was more likely to be correlated with habitat volume in Panama than in Illinois or Minnesota, and species relative abun- dances were more similar between years in Panama than in Illinois or Minnesota streams, especially in pools. These patterns suggest that in streams subject to strong seasonal and annual environmental variation, habitat features are poorer predictors of fish distribution and abundance than in streams subject to less environmental variability. We speculate that annual variability in reproductive success and harsh winters interact to maintain imbalance between the fish assemblages and their habitat in Minnesota. Weak relationships between species richness and habitat volume or complexity may be indicative of population vari- ability and the predominance of extinction/recolonization processes in community orga- nization.

Early Successional Patterns of Forest Species: Interactions of Life History Traits and Disturbance

Abstract: Patterns of abundance were examined for vascular plant species during 21 yr of succession in two clear-cut and burned Pseudotsuga forests in the western Cascade Range of Oregon. A majority of forest understory species persisted through disturbance. Most colonizing species established within 2 yr after burning. Individualistic species re- sponses were described by a series of broadly overlapping, unimodal curves of constancy and canopy cover, differing in time of initiation, duration, and magnitude. Thus, early successional change was characterized by gradual shifts in the abundance of generally persistent species. Eleven population patterns (species groups) were identified. Interactions of life history traits and disturbance explain the temporal trends of the most common species. Within the groups of invading species, the timing of initial establishment, as well as the timing and magnitude of peak abundance were related to the origin of propagules, phenological traits, potential for vegetative expansion, and temporal and spatial variation in disturbance. Abundance patterns of invading species were also influenced by stochastic and historical factors. Contrasting responses of species between sites reflected differences in histories of logging and slash burning. Within the groups of residual species, temporal patterns of abundance reflected initial species distributions, resistance to logging and burning distur- bance, mode of reproduction, morphological traits, and spatial variation in disturbance intensity. These observations suggest that early secondary succession in Pseudotsuga forests has a deterministic component, founded in the life history traits of the available species, and

Patterns of plant species richness along riverbanks

Abstract: We studied bank vegetation between the spring high-water level and the summer low-water level along two rivers in northern Sweden. The hypothesis that natural and ruderal species would show different downstream patterns of species richness was tested by sampling species composition and environmental variables along 200 m long stretches of riverbank, 10 km apart. Natural species richness was highest in the midreaches of both rivers, whereas ruderal species showed a significant, monotonic increase down- stream. There are no obvious mechanisms producing the quadratic pattern of natural species richness. The downstream increase in ruderal species suggests a founder effect depending on larger artificial disturbances near the coast, but alternative explanations are also given. Total species richness did not exhibit any interpretable downstream patterns. The only factors significantly correlated with total species richness along both rivers were substrate heterogeneity and substrate fineness. Total species richness increased with substrate het- erogeneity and was at maximum at intermediate levels of substrate fineness. This suggests that co-occurrence of natural and ruderal species is most likely where substrate types are numerous and dominant substrate particle size intermediate. Kep u'ords. natural species; northern Sweden; riparian vegetation; river; riverbank; ruderal species;

Fishes and Decapod Crustaceans of Cape Cod Eelgrass Meadows: Species Composition, Seasonal Abundance Patterns and Comparison with Unvegetated Substrates

Abstract: Bimonthly trawl samples from eelgrass and nearby unvegetated areas on Cape Cod, Massachusetts, showed greater species richness in eelgrass meadows relative to unvegetated areas, and greater summer abundance in vegetation for decapod crustaceans and fishes. The composition of eelgrass-associated decapods and fishes was dominated by cold-water taxa and was strikingly different from that of the better studied eelgrass meadows of the mid-Atlantic coast. Four of the eight decapod species collected, including the second and third most abundant taxa, do not even appear in collections reported from Chesapeake Bay eelgrass meadows. Similarly, 10 of the 22 fish species taken, including the first and sixth most abundant species, are not reported from Chesapeake Bay eelgrass samples. Cape Cod eelgrass beds seem to play a nursery role for several commercially important fish species, although the nursery function is less obvious than in previously studied mid-Atlantic eelgrass meadows.

Taxonomy, Phylogeny and Biogeography of Mushroom Corals (Scleractinia: Fungiidae)

Abstract: The Fungiidae are mushroom corals that live in sublittoral habitats in the tropical Indo-Pacific. Their habitats are part of coral reefs or other marine substrata, which usually can be found in the proximity of the reefs. In the present taxonomic revision, the family is divided into 11 genera; one of which, Fungia, is subdivided into seven subgenera. A total of 40 species is described and figured, three of which are new to science. One species is renamed. The stratigraphic distribution is given for all the species recorded in fossil state. A tentative phylogenetic reconstruction down to the species level is given. The cladogram that is provided should be considered a working hypothesis and not a sound basis for a completely revised classification and nomenclature of the Fungiidae. For each species the presently known geographic range is mapped. The pattern of species richness in the Indo-Pacific is compared with that of some other taxa and discussed with respect to their distributional patterns. The ranges of the Fungiidae are analyzed with the use of approaches from both historical and ecological biogeography.

Biogeographic Associations in Fish Assemblages: Local vs. Regional Processes

Abstract: Six geographic regions along the Laurentian Great Lakes in Ontario, represented by 286 lakes, were examined to identify the existence of regional similarities of fish species composition and their association to geographic location and regional patterns of lake morphology and pH. Lakes differed significantly among regions with respect to surface area, maximum depth, and pH. Species presence/absence data were summarized using correspondence analysis, and the resultant scores were used in multivariate analysis of variance and canonical variates analysis. These results indicated that the fish faunas of the six geographical areas were distinct. Interregional distances based on fish community scores, lake morphology–chemistry data, and geographical distances were contrasted using Mantel's test. Regional faunal similarities were correlated significantly with geographical proximity, but not with lake morphology. We propose that post—glacial dispersal and lake thermal regimes are important determinants in structuring regional patterns of fish assemblages, whereas environmental conditions such as lake depth and pH assume greater importance in determining species compositions of individual lakes.

Patterns in tree species richness as a test of the glacial extinction hypothesis

Abstract: IT is well established that Europe has far fewer tree species and genera than either eastern North America or eastern Asia1–3. Fossil evidence shows that west-central Europe had a much richer tree flora during the Upper Tertiary (25–2 Myr BP), with many genera which now survive only in temperate regions of North America and Asia3. These trees seem to have been eliminated from Europe during cold, dry glacial periods of the Pleistocene Era (2–0.001 Myr BP). Their failure to recolonize may be due to a failure of species to reach potential refugia during the glacial phase2,3. Alternatively, present-day climates, rather than purely historical effects of extinction or suvival in refugia, may explain the observed contrasts in richness between regions. Currie and Paquin4 showed that the number of tree species in Britain and Ireland corresponds to that of North American areas of similar climate, without the need to invoke the historical explanation. Here we report that the differences in species richness between three northern temperate regions, Europe, eastern North America and eastern Asia, can be mainly explained in terms of present-day climatic factors. Similarly, and despite its long period of isolation from the northern temperate flora, the tree flora of New Zealand corresponds closely to the same relationship between climate and species richness. By contrast, greater species richness (compared with Europe and North America) found in some parts of eastern Asia cannot readily be accounted for in terms of present climate, and may be due to lower rates of extinction during glacial phases.

Differential effects of above- and below-ground insect herbivory during early plant succession

Abstract: The effects of aboveand below-ground insect herbivory on a natural plant community colonising bare ground were determined by manipulative field experiments. A foliar insecticide (Dimethoate-40) and a soil insecticide (Dursban 5G) were applied separately and in combination in a factorial experimental design over a two-year period. Characteristics of the developing vegetation were assessed in insecticidetreated and control plots. The insecticides had no independent effect on plant growth. Plant species richness and diversity were increased by the application of soil insecticide and, by the second season, depressed by foliar insecticide. Vegetation frequency and particularly cover abundance were enhanced by both compounds, with the soil insecticide having a greater effect in the second year. Vegetation height, assessed by a weighted mean height index, was only increased by the application of soil insecticide in the first year. Three major life-history groupings (annual and perennial herbs and perennial grasses) responded differently to herbivory. Annual herbs were promoted by foliar and soil insecticides in the first season, but only by the latter in the second. Within this general pattern, common species varied in response to the two compounds. Perennial grasses were strongly promoted by foliar insecticide and although few perennial herbs were present these increased in number of species and cover when below-ground herbivory was reduced. The different responses of life-history groupings and individual species to the two types of herbivory have a considerable effect on the pattern of early succession. The role of herbivory in relation to competition and seedling mortality in the developing plant community are discussed. The latter is relevant to the creation of species-rich communities of potential conservation value.

Island Biogeograhy of Montane Forest Mammals in the American Southwest

Abstract: Information from packrat (Neotoma spp.) middens and other paleoenviron- mental indicators was used to reconstruct Pleistocene distributions of macrohabitats in the American Southwest (Arizona, New Mexico, and southern Utah and Colorado). This revealed a system of southern montane forests that were isolated during the Pleistocene (primarily by woodlands) as well as today (by grasslands, chaparral, and desertscrub). Based on the presence of at least five species of nonvolant forest mammals on these montane islands, we inferred that these mammals immigrated across woodlands during the Pleis- tocene. Because the great majority of montane forests in the American Southwest are now isolated by woodlands, but not grasslands, chaparral, or desertscrub, we hypothesized that post-Pleistocene immigrations may influence the structure of mammalian communities on these montane islands. This hypothesis was supported by the highly significant correlation of mammalian species richness with current isolation as well as area (P < .01 for simple correlations and for partial correlations after removing effects of latitude and area or isolation: 26 species, 27 islands). When isolation was partitioned into distance to be traveled across woodland vs. grassland-chaparral habitats, species richness was significantly correlated with the latter measure of isolation (P < .01) but not with the former, indicating that woodlands do not represent major barriers to immigration. Seventeen of 26 species considered are reported with at least 10% of their record locations in woodlands and other low-elevation habitats. Analyses of patterns of occurrence of seven species of forest mammals inhabiting between 7 and 16 islands revealed that insular distribution was significantly (P < .01) affected by area in two species, by area and isolation in three species, and by isolation alone in the remaining two species. Based on our reconstruction of Pleistocene macrohabitat distributions, analyses of community- and species-level patterns, and evidence on the ability of forest mammals to inhabit and disperse across woodlands and other low-elevation habitats, we conclude that community structure of montane forest mammals in this region of the American Southwest is influenced by post-Pleistocene immigrations as well as extinctions.

Reductions in plant species richness under stands of alien trees and shrubs in the Fynbos Biome.

Abstract: Synopsis The reduction of species richness of indigenous plants is one of the major problems associated with the presence of dense stands of invasive alien trees and shrubs in the Fynbos Biome of the Cape Province, South Africa. A synthesis was made of published and unpublished data on plant species richness in fynbos with different levels of invasion and different histories of control. Linear regressions of species richness on the log of quadrat size were significant for both uninvaded fynbos and fynbos under dense stands of alien trees and shrubs. The slopes of the regression equations did not differ significantly between invaded and uninvaded sites, but elevations were significantly different, indicating a marked reduction in richness of indigenous plant species in invaded areas. The linear regression of species richness on quadrat size for cleared areas was not significant, but quadrats at most cleared sites showed species richness values intermediate to those of uninvaded fynbos and dense stands of a...

Role of Uprooting in Composition and Dynamics of an Old‐growth Forest in Japan

Abstract: Seedling, sapling, and tree composition in several types of gap and nongap microsites were examined in an old-growth temperate mixed forest in western Japan. The distribution of species was not related to gap size (10-340 m2). Seedling communities on tip-up mounds and those on fallen boles of coniferous trees were rich and composed of pioneer species. In contrast, understory composition in gaps without uprooting did not differ from undisturbed forest. Dwarf bamboo, which dominates the forest floor and pre- vents tree regeneration, magnifies the effect of uprooting. Species with small, wind-dispersed seeds were found mainly on disturbed soil, while species with large, animal-dispersed seeds did not have any bias in distribution. Soil disturbance is a more important feature of the disturbance regime of this forest than is gap formation, with regards to maintaining species richness.

Year-to-year variation in the aquatic macroinvertebrate fauna of a northern California stream

Abstract: The benthic macroinvertebrate community of a third-order coastal stream in northern California was examined in mid May (end of the wet season) and late August (near the end of the dry season in the prevailing Mediterranean climate of the region) over a 7-yr period in which there was substantial year-to-year variability in precipitation and, consequently, stream discharge. Ephemeroptera, Trichoptera, and Diptera were the dominant components of the macrobenthic community, accounting for 93% of total individuals and 62% of the 81 taxa collected in mid May, and 96% of total individuals and 64% of the 69 taxa collected in late August. In mid May, significant reductions in species richness and Simpson's diversity were observed during a year of extreme drought and in years with above-average wet season rainfall. Macroinvertebrate density decreased and relative abundance of Chironomidae increased as wet season rainfall increased. In late August, year-to-year variability in community parameters measured was substa...

Interspecific competition increases local extinction rate in a metapopulation system

Abstract: THE importance of interspecific competition for the distribution and abundance of organisms has been hotly debated during the last decade1-7. Although many field experiments have shown effects of interspecific competition on abundance and reproduction1,3, there is no unequivocal experimental evidence that interspecific competition can influence rates of local extinction in the field. Here I report that in a long-term field experiment with artificial rockpools, interspecific competition between three common rock-pool zooplankton species led to increased local extinction rates. In addition, studies of the distributional dynamics of the species in natural rockpools also showed that interspecific competition increases extinction rates. These results imply that interspecific competition is likely to limit the regional richness of species in the rockpool metapopulation system. MacArthur and Wilson8 were the first to suggest that an increase in extinction rate per species with an increase in the number of species could influence species richness on islands. Moulton and Pimm9 found that this was so among birds introduced to the Hawaiian islands, but the present study is the first field experiment providing unequivocal evidence of the effect.

West African rivers as biogeographic islands: species richness of fish communities.

Abstract: Some factors influencing the species richness of West African fish communities were studied in a sample of 26 rivers using four habitat and hydrologic variables. Analysis of a larger sample of 39 rivers showed that species richness was positively related to area. A power function with an exponent of 0.32 gave the best fit. As the surface area used was that of the catchment area and not that (unknown) of the river, the biological significance of this relationship and the possibilities of comparison were limited. Ridge regression analysis and forward stepwise selection indicated that a model that explained ln(species richness) as a function of ln(mean annual discharge) and ln-(catchment surface area) was best, accounting for 90% of the variance of the dependent variable. The combination of surface area and discharge was presumed to act through the volume of water available for the fishes and habitat productivity. Habitat diversity, measured by the diversity of the terrestrial vegetation covering the catchment area, had no significant positive effect when surface area was used in the regression. Rivers (“islands”) should have fewer species than tributaries of similar size since, for fishes within a river system (“continent”), there is free circulation between all its branches. The model derived from the river data underestimated the species richness of a sample of 11 tributaries. This was compatible with the hypothesis of higher population extinction rates in insular biotopes. The residuals of the linear model did not show random geographical distribution; the rivers in some areas had more species than expected. The possibility that historical factors, especially Quaternary climatic variations, might cause this distribution is discussed.

Elevational Patterns of Species Richness, Evenness, and Abundance of the Costa Rican Leaf-Litter Herpetofauna

Abstract: The abundance, species richness, and evenness of the Costa Rican leaf-litter herpetofauna was estimated during the late wet season of 1985 by quantitative sampling of replicate plots at ten sites encompassing an elevation range of 3 to 1670 m. Species richness was positively correlated with leaf-litter depth, and negatively correlated with elevation. Herpetofaunal density also tended to increase with litter depth and decline with elevation. A strong positive correlation existed between species richness and herpetofaunal density. Evenness was highly variable and independent of both leaf-litter depth and elevation. Analysis of a subset of the data, representing an elevational transect from Tortuguero to the Braulio Carrillo National Park Extension, yielded similar results. Tropical leaf-litter reptiles and amphibians appear to be both more diverse and more abundant at lower elevations. Sites with deep leaf litter generally sustain dense and diverse reptile and amphibian populations. Local herpetofaunas typically consist of a few very common species along with a large number of comparatively rare species. REPTILES AND AMPHIBIANS are a major constituent of the fauna inhabiting tropical forest litter. Studies of tropical leaf-litter herpetofaunas have emphasized patterns of abundance and distribution among geographic regions (Lloyd et al. 1968; Heyer & Berven 1973; Scott 1976, 1982; Inger 1980a, b; Heatwole 1982), vegetational zones (Brown & Alcala 1961, Heatwole & Sexton 1966, Heyer 1967), and elevational gradients (Brown & Alcala 1961, Scott 1976) as well as seasonal changes (Lieberman 1982, 1986). It has become generally accepted that leaf-litter reptiles and amphibians are more abundant in the New World Tropics than in Southeast Asia (Scott 1976, Inger 1980b, Duellman & Trueb 1986) although the exact reason remains a subject of debate (May 1980). Similarly, the general consensus is that the abundance of tropical leaf-litter herpetofaunas increases with increasing elevation, while species richness and equitability both decline (Brown & Alcala 1961, Scott 1976, Heatwole 1982, Duellman & Trueb 1986). Scott (1976) attributed this pattern to greater overall forest productivity at intermediate elevations, coupled with increased densities of the most common species at higher elevations. Before attempting to determine the mechanisms responsible for observed patterns of tropical leaf-litter herpetofaunal abundance and diversity, we must document the phenomenon conclusively. Previous quantitative studies have sampled few sites, have been unable to provide replicated samples (Brown & Alcala 1961), or may have confounded site and year effects by sampling different sites in different years (Scott 1976). We surveyed the Costa Rican leaf-litter herpetofauna by quantitatively sampling replicate plots at ten sites, ranging from 3 to 1670 m in elevation, during the late wet season of July-September 1985. Our sampling strategy permitted statistical analyses to determine the relationship between litter depth and elevation, and leaf-litter herpetofaunal richness, evenness and abundance. The results of our study contradict several of the generally accepted patterns of tropical leaf-litter herpetofaunal abundance and diversity.

Distribution of vascular plant species in small woodlands on the Western Carpathian foothills

Abstract: Sixty-nine woodlands isolated in the agricultural landscape of the Wierzban6wka valley (Western Carpathian foothills) were investigated. An analysis of historical maps shows that most of the woods under study are remnants of ancient woodlands. Stepwise and partial regression analyses were used in the statistical study of 66 small woods. It was found that the number of woodland vascular plant species depended upon area, isolation, shape, period of isolation and anthropogenic disturbances. Recent woods are poorer in species than the ancient ones. Single ancient woods on average support fewer species than does a combination of several small ancient woods of the same total area. The distribution of 58 common and 56 locally rare woodland species was analysed. The group of common species associated with more recently isolated and less disturbed woods contained more myrmecochores, endozoochores and epizoochores and fewer anemochores than did the group of indifferent species. This last group included more species capable of colonizing recent woods. The number of woodland species appeared to be the most important predictor of the number of rare species. The results obtained and their comparison with the results from other similar studies indicate that small remnants of ancient forests in an agricultural landscape are refuges of numerous woodland species. Therefore, the preservation of such woods carries great weight in the maintenance of species richness and the protection of woodland species.

Secondary Succession, Gap Dynamics, and Community Structure in a Southern Appalachian Cove Forest

Abstract: Forest succesion was studied in a species—rich cove forest of the Great Smoky Mountains, Tennessee. Long—term compositional and structural changes in secondary stands, 15—63 yr after agricultural abandonment circa 1920, were compared to an adjacent old—growth stand. Later successional trends were projected by computer simulation. The colonizing stand (15 yr) was dominated by Liriodendron tulipifera and Robinia pseudoacacia. Common old—growth species absent at this early stage included Aesculus octandra, Fagus grandifolia, and Tsuga Canadensis. By year 40, Liriodendron dominated the overstory and all old—growth dominants were represented in the understory. After 60 yr, Acer saccharum was clearly the most abundant understory species; gap model projections indicated that after 200 yr it will dominate the forest. The actual old—growth stand was dominated by Acer saccharum. Species richness peaked at mid—succession (°50 yr), while diversity (H') and evenness (J') of species biomass were highest at the old—growth stage. Richness peaked with the coexistence of shade—intolerant colonizers in the overstory and shade—tolerants in the understory. Canopy—gap processes of the secondary and old—growth stands differed sharply. The old—growth canopy was composed of large, spreading, and overlapping crowns, while the second—growth stand was composed of narrow, nonoverlapping crowns. Gaps in the secondary stand tended to be small (<100 m2) but numerous. The regeneration of intolerants was low and individual gap microsites were not markedly different from the understory as a whole. Old—growth gaps were often larger, higher light microsites which contrasted sharply with the shaded forest floor. The wider range of gap sizes in old forests accommodates a variety of species, including intolerants, contributing to the high canopy species diversity of old—growth cove forests.

Classification of water beetle assemblages in arable fenland and ranking of sites in relation to conservation value

Abstract: SUMMARY. 1. Water beetles were recorded from 157 sites around the Wash, England, in 1986. Most sites were ditches in arable land. Eight main types of water beetle assemblage were identified by multivariate analysis. The habitats of these assemblages were characterized by measurement of a range of physical and chemical factors. 2. Of the 130 species recorded, four are listed in the British Red Data Book and a further thirty-five are rated as Nationally Notable. Records from 1904 to 1938 for the same area indicate that only three species have been lost in the subsequent period of intensification of water management and arable farming. A rich water beetle fauna can thus survive in drainage systems in arable fen. 3. Vegetation management was important in maintaining the ‘species quality score’, proposed as a measure of conservation value, of larger ditches but management reduced the species quality of one type of assemblage associated with smaller ditches. One type of assemblage was found only in ditches subject to management.

Leafy spurge and the species composition of a mixed-grass prairie.

Abstract: The relationship between leafy spurge (Euphorbia esula L.) and the species composition of mixed-grass prairie was examined on both a large scale, within a 200-km2 area, and on a local scale, within a single infestation. On the large scale, cover values of 8 of the 10 most common species varied significantly (P & 0.05) between native prairie and spurge-dominated vegetation. Cover values of all common native species were negatively correlated with cover of leafy spurge. Within a single infestation of leafy spurge, the frequency of 5 common native species decreased significantly with leafy spurge. Most native species were absent where leafy spurge was most abundant and species richness declined from 11 outside the infestation to 3 at the center. Ninety-five percent of leafy spurge infestations within a 374-ha area were associated with anthropogenic disturbances (vehicle tracks, road construction and fireguards) which removed native plant cover and exposed mineral soil. These observations corroborate experimental studies which show that leafy spurge establishes more readily in disturbed soil and indicate that the result of such disturbances is the replacement of native species with leafy spurge.

Distribution and Abundance of Adult Aquatic Insects in the Forest Adjacent to a Northern California Stream

Abstract: The distribution of adult aquatic insects in the mixed evergreen forest adjacent to Big Sulphur Creek, Sonoma Co., Calif., was examined using sticky traps (0.26 m2 each) that were placed in trees at three distances (5, 40, 150 m) from the stream and at three heights (2, 5, 8 m) above the ground. Species richness, number of individuals, and biomass of aquatic insects, and number of individuals for seven of 12 common aquatic insect taxa decreased (P ≤ 5 0.05) as distance from the stream increased. Species richness, number of individuals, and biomass of aquatic insects showed no relationship with height above the ground, but of the 12 common taxa, three were most abundant near tree tops and one was most abundant near tree bases (P ≤ 0.05). Adult aquatic insects represented 36.9 and 15.4% of total arthropod numbers and 25.3 and 10.7% of total arthropod biomass at the 5-m and 150-m sites, respectively. The abundance of adult aquatic insects in the forest bordering this stream suggests that adult aquatic insects provide an important conduit for energy and nutrients from the aquatic system to the terrestrial food web.

Response to organic enrichment of infaunal macrobenthic communities under salmonid seacages

Abstract: The response of infaunal macrobenthic communities beneath salmonid seacages to solid organic wastes (food pellets and fish excreta) was tested by means of the ABC-method (abundance, biomass comparison method: Warwick 1986) on samples collected from the SAFCOL seafarm at Badger Cove, southeast Tasmania, from February to July 1988. The intermittent nature of the addition of organic waste allowed us to monitor decline and recovery of the macrofauna, i.e., harvesting of a cage permitted a period of recovery whilst restocking precipitated a decline. The ABC-method proved to be a sensitive indicator of community health. Under a normal feeding regime the macrofaunal community structure indicated a moderately disturbed condition. Only 7 wk after the cage was harvested, species richness had increased markedly and the community adopted an undisturbed condition. Further improvement was apparent 14 wk post-harvest. Similarly, a decline to a moderately disturbed condition was apparent 7 wk after restocking and species richness had declined. No such changes occurred under a cage which contained fish continuously over the same period.

Comparative Population Ecology of Eleven Species of Rodents in the Chihuahuan Desert

Abstract: Comparisons of mark-recapture data on life histories and population dy- namics of the 1 1 commonest species of nocturnal desert rodents inhabiting our experimental study site in the Chihuahuan Desert of extreme southeastern Arizona permitted assessment of the role of evolutionary relationships and ecological factors in the coexistence of these species. The species varied greatly in population density, extent of interannual variation in abundance, timing of reproduction, extent to which reproduction was seasonal, rate of disappearance of marked individuals, frequency and distance of lifetime dispersal move- ments, but perhaps less so in death rate and maximum longevity. Most of the species showed positively correlated year-to-year fluctuations in population density, suggesting that they responded similarly to interannual variation in precipitation, primary production, and availability of food resources. In contrast, there were both positive and negative correlations in seasonal patterns of reproductive activity and population density. Lifetime dispersal movements were inversely related to body size, suggesting that energy constraints cause the smallest species to move among rich patches in a coarse- grained manner. Patterns of similarities and differences among closely related (congeneric and confamilial) species suggested that evolutionary constraints sometimes, but not always, limited variation in life history and demography. The relationship between population ecology and competition among these species was not clear. We interpret the diversity of life histories and population dynamics in these coexisting species to be a consequence of: (a) a productive and spatially and temporally variable environment that provides a variety of resources that may be used in different ways, (b) historical biogeographic events that have made available a large regional pool of species from which potential colonists can be drawn, and (c) differences in population ecologies among the species that evolved primarily in other environmental contexts, but that permit coexistence by enabling the species to use different resources or to use the same resources in different ways.

Species richness – standing crop relationships along four lakeshore gradients: constraints on the general model

Abstract: The applicability of a model describing the relationship between species richness and standing crop and litter was tested in each of four lakeshore habitats within Wilsons Lake, Nova Scotia. The shapes of the curves describing the species richness – standing crop relationships in the four habitats were significantly different. Standing crop and litter values were positively correlated with measured indices of soil fertility (loss on ignition and silt and clay content) and negatively correlated with disturbance as determined by the location of the shrub zone and overwinter damage to wooden pegs. Sites with high standing crop had a lower proportion of biomass composed of evergreen and isoetid species than the proportion in sites where standing crop was low. The among habitat variation observed in this study, and the variation in published values of standing crop values yielding maximum species richness, limit the accuracy of predictions from this model. Steps for refinement are suggested.

Geographic variation and community structure in an ant-plant mutualism: Azteca and Cecropia in Costa Rica

Abstract: The association between Azteca ants and Cecropia trees is the most conspicuous ant-plant mutualism in the neotropics, yet little is known about the identities or community ecology of the species involved. A survey of ant communities found in Costa Rican Cecropia trees revealed a community of Azteca species obligately associated with Cecropia, and a diverse assemblage of non-obligate ants in a variety of genera. High occupation rates of Cecropia saplings and trees, and presence of many incipient colonies in saplings vs single colonies in trees, suggest that Cecropia are a limiting resource for which ants compete. Obligate Azteca appeared competitively superior to non-obligate ants, since non-obligate ants were never found dominating mature trees. Competitive relationships between obligate Azteca were not clear; local communities contained three to four Azteca species using the same host tree species resource. Two Azteca species had a parapatric distribution, the zone of parapatry co-occurring with a similar zone of parapatry between two Cecropia species. At the boundary, the Azteca species were not host specific. Possible factors influencing the outcome of competition between ants for Cecropia trees include queen and worker behavior, priority effects, partial hostplant specialization, and habitat specialization. Explanation of current distributions may require knowledge of historical factors and stochastic effects. SPECIALIZED MUTUALISMS BETWEEN ANTS AND MYRMECOPHYTES are not isolated pairs of interacting species. They usually involve communities of many species. Myrmecophytes, as used here, are plants that produce cavities (domatia) within which specialized ants nest. Myrmecophytic Acacia trees in Central America are occupied by several Pseudomyrmex species (Janzen 1967, 1973a), at least one of which is a parasite rather than a mutualist (Janzen 1975). Leonardoxa africana in Cameroon is occupied by the mutualist Petalomyrmex phylax and the parasite Cataulacus mckeyi (McKey 1984). New World Triplaris are inhabited by sympatric species of Pseudomyrmex, and Old World Barteria by sympatric species of Tetraponera (P. S. Ward, pers. comm.). Cordia aliodora in Costa Rica is occupied by sympatric populations of Azteca longiceps and Zacryptocerus setulifer (pers. obs.). Examining the structure and spatial variation of these communities may provide insight into how specialized mutualisms evolve and are maintained. Wilson (1987) reported a very rich arboreal fauna occupying single rain forest tree canopies in Peru, and raised questions regarding the mechanisms promoting such high local species richness. Communities of myrmecophytes and their ants provide a microcosm within which to examine the community ecology of arboreal ants. By examining a specialized ant-plant interaction at the community level one can address the following questions. What is the spatial variation in community composition? Do ants exhibit hostplant specificity? Are plants a limiting resource for ants? What factors influence the outcome of competition between ants for plants? Results from a study of an ant-plant community in Peru suggest that a variety of ants do compete for plants, and that specialized inhabitants are competitively superior (Davidson et al., in

Ecology of deep-sea nematodes from the Puerto Rico trench area and Hatteras Abyssal plain

Abstract: Nematode assemblages from a bathyal silty-sand and three hadal silty-clays from the Puerto Rico Trench area were compared with that from a silty-clay from the HatterasAbyssal Plain. Fine sediments at each site were largely dominated by species belonging to three major genera: Theristus, Acantholaimus and Halalaimus . At the bathyal sand site the relative abundances of these genera were reduced and those of several others (e.g. Desmodora, Leptolaimus, Camacolaimus, Tricoma, Greeffiella, Setoplectus ) elevated. Average body weight of nematodes occurring in the sand was 0.057 μg (dry weight), approximately 20–50% that of the nematodes found in the silty-clays. It is suggested that in the deep sea, as at shallow depths, smaller nematodes are better able to move in heterogeneous, coarser sediments than in more uniform, fine ones. Deposit-feeding species were the dominant feeding type observed in all sediments, but epistrate feeders were most numerous in the bathyal sands, probably the result of increased resource partitioning by worms inhabiting a more heterogeneous sedimentary environment. Species richness in bathyal sands was also high. Normal classification of assemblages found in sediments from the Hatteras Plain, Puerto Rico Trench areas, Venezuela Basin and upper abyssal province off North Carolina suggests that deep-sea nematode families and genera are widely distributed across the Antillean Arc. However, species endemism is high: 67 and 77% of the species identified from the Hatteras Plain and Puerto Rico Trench respectively, occurred only at these sites. Affinities among species from all four sites were very low. The wide distribution of families and genera, and narrow distribution of species, suggests that current radiation of deep-sea nematodes probably occurs at the species level.

Elevational zonation of mammals in the central Philippines

Abstract: Trapping and netting of small mammals on a land-bridge island (Leyte) and on an oceanic island (Negros) revealed similar patterns of elevational change in abundance and species richness. Fruit bats (Pteropodidae) reached their greatest local densities in agricultural areas, and were least abundant in montane mossy forest. The fruit bats found to be common in agri- cultural areas are widespread in Southeast Asia: in contrast, species that were most common in forested areas are Philippine endemics. Fruit bat abundance was greater on the oceanic island than on the land-bridge island. Trappable small mammals (families Soricidae and Muridae) showed no change in species richness with increasing elevation, but did show a gradual increase in overall abundance. Even though the oceanic island was depauperate of non-volant mammal species, it had the higher abundance of non-volant mammal individuals; however, this may have been due primarily to differences associated with the elevation of sampling sites. Murid rodents at the higher elevations on Leyte tend to be those that are members of the old endemic group of Philippine murids, and those at lower elevations tend to be members of more recently arrived groups. Most non-volant small mammals at all elevations on the oceanic Negros, and in agri- cultural areas on Leyte, are non-native species.