Journal of Animal Ecology
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A truce with neutral theory: local deterministic factors, species traits and dispersal limitation together determine patterns of diversity in stream invertebrates Summary
Studies seeking to explain local patterns of diversity have typically relied on niche explanations, reflected in correlations with local environmental conditions, or neutral theory, invoking dispersal processes and speciation. We used macroinvertebrate community data from 10 streams that varied independently in local ecological conditions and spatial proximity. Neutral theory predicts that similarity in communities will be negatively associated with distance between sites, while niche theory suggests that community similarity will be positively associated with similarity in local ecological conditions. Similarity in total invertebrate, grazer and predator assemblages showed negative relationships with distance and, for grazers and predators, positive relationships with local ecological conditions. However, the best model predicting community similarity in all three cases included aspects of both local ecological conditions and distance between sites. When assemblages were analysed according to dispersal ability, high‐dispersal species were shown to be freely accessing all sites and community similarity was not well predicted by either local ecology or spatial separation. Assemblages of species with low and moderate dispersal ability were best predicted by combined models, including distance between sites and local ecological factors. The results suggest that the perceived dichotomy between neutral and local environmental processes in determining local patterns of diversity may not be useful. Neutral and niche processes structured these communities differentially depending on trophic level and species traits. We emphasize the potential for both dispersal processes and local environmental conditions to explain local patterns of diversity.
Journal of Animal Ecology - Tập 75 Số 2 - Trang 476-484 - 2006
Behavioural Adjustment of Population Density to Available Food by Juvenile Atlantic Salmon
Journal of Animal Ecology - Tập 40 Số 3 - Trang 569 - 1971
Relative role of deterministic and stochastic determinants of soil animal community: a spatially explicit analysis of oribatid mites Summary 1. Ecologists are debating the relative role of deterministic and stochastic determinants of community structure. Although the high diversity and strong spatial structure of soil animal assemblages could provide ecologists with an ideal ecological scenario, surprisingly little information is available on these assemblages.2. We studied species‐rich soil oribatid mite assemblages from a Mediterranean beech forest and a grassland. We applied multivariate regression approaches and analysed spatial autocorrelation at multiple spatial scales using Moran’s eigenvectors. Results were used to partition community variance in terms of the amount of variation uniquely accounted for by environmental correlates (e.g. organic matter) and geographical position. Estimated neutral diversity and immigration parameters were also applied to a soil animal group for the first time to simulate patterns of community dissimilarity expected under neutrality, thereby testing neutral predictions.3. After accounting for spatial autocorrelation, the correlation between community structure and key environmental parameters disappeared: about 40% of community variation consisted of spatial patterns independent of measured environmental variables such as organic matter. Environmentally independent spatial patterns encompassed the entire range of scales accounted for by the sampling design (from tens of cm to 100 m). This spatial variation could be due to either unmeasured but spatially structured variables or stochastic drift mediated by dispersal. Observed levels of community dissimilarity were significantly different from those predicted by neutral models.4. Oribatid mite assemblages are dominated by processes involving both deterministic and stochastic components and operating at multiple scales. Spatial patterns independent of the measured environmental variables are a prominent feature of the targeted assemblages, but patterns of community dissimilarity do not match neutral predictions. This suggests that either niche‐mediated competition or environmental filtering or both are contributing to the core structure of the community. This study indicates new lines of investigation for understanding the mechanisms that determine the signature of the deterministic component of animal community assembly.
Journal of Animal Ecology - Tập 81 Số 1 - Trang 214-221 - 2012
Partial migration in tropical birds: the frontier of movement ecology
image A. E. Jahn, D. J. Levey, J. A. Hostetler & A. M. Mamani (2010) Determinants of partial bird migration in the Amazon Basin. Journal of Animal Ecology , 79 , 983–992. Partial migration, in which only some individuals of a species migrate, might be central to the evolution of migratory behaviour and is likely to represent an evolutionary transition between sedentariness and complete migration. In one of the few detailed, individual‐based migration studies of tropical birds, Jahn et al. study the partial migration system of a South American bird species for the first time. Food limitation forces the large adult males and small, young females to migrate, contrary to the expectations of the body size and dominance hypotheses. This study confirms the importance of food variability as the primary driver of migratory behaviour. There is urgent need for similar studies on the movement ecology of understudied tropical bird species, whose diversity of migratory behaviour can shed light on the evolution of bird migration.
Journal of Animal Ecology - Tập 79 Số 5 - Trang 933-936 - 2010
Dispersal in Dipterans: Its Costs and Consequences
Journal of Animal Ecology - Tập 46 Số 2 - Trang 443 - 1977
Dispersal‐related life‐history trade‐offs in a butterfly metapopulation Summary Recent studies on butterflies have documented apparent evolutionary changes in dispersal rate in response to climate change and habitat change. These studies often assume a trade‐off between dispersal rate (or flight capacity) and reproduction, which is the rule in wing‐dimorphic species but might not occur equally in wing‐monomorphic species such as butterflies. To investigate the relationship between dispersal rate and fecundity in the Glanville fritillary butterflyMelitaea cinxia we recorded lifetime individual movements, matings, ovipositions, and maximal life span in a large (32 × 26 m) population cage in the field. Experimental material was obtained from 20 newly established and 20 old local populations within a large metapopulation in the Åland Islands in Finland. Females of the Glanville fritillary from newly established populations are known to be more dispersive in the field, and in the cage they showed significantly greater mobility, mated earlier, and laid more egg clutches than females from old populations. The dispersive females from new populations exhibited no reduced lifetime fecundity in the cage, but they had a shorter maximal life span than old‐population females. These results challenge the dispersal–fecundity trade‐off for nonmigratory butterflies but instead suggest a physiological trade‐off between high metabolic performance and reduced maximal life span. High metabolic performance may explain high rates of dispersal and oviposition in early life. In fragmented landscapes, an ecological trade‐off exists between being more dispersive and hence spending more time in the landscape matrix vs. having more time for reproduction in the habitat. We estimate with a dispersal model parameterized for the Glanville fritillary that the lifetime egg production is 4% smaller on average in the more dispersive butterflies in a representative landscape, with much variation depending on landscape structure in the neighbourhood of the natal patch, from −26 to 45% in the landscape analysed in this paper.
Journal of Animal Ecology - Tập 75 Số 1 - Trang 91-100 - 2006
State‐dependent risk‐taking by green sea turtles mediates top‐down effects of tiger shark intimidation in a marine ecosystem
Journal of Animal Ecology - Tập 76 Số 5 - Trang 837-844 - 2007
Reefscapes of fear: predation risk and reef hetero‐geneity interact to shape herbivore foraging behaviour Summary
Predators can exert strong direct and indirect effects on ecological communities by intimidating their prey. The nature of predation risk effects is often context dependent, but in some ecosystems these contingencies are often overlooked. Risk effects are often not uniform across landscapes or among species. Indeed, they can vary widely across gradients of habitat complexity and with different prey escape tactics. These context dependencies may be especially important for ecosystems such as coral reefs that vary widely in habitat complexity and have species‐rich predator and prey communities. With field experiments using predator decoys of the black grouper (Mycteroperca bonaci ), we investigated how reef complexity interacts with predation risk to affect the foraging behaviour and herbivory rates of large herbivorous fishes (e.g. parrotfishes and surgeonfishes) across four coral reefs in the Florida Keys (USA). In both high and low complexity areas of the reef, we measured how herbivory changed with increasing distance from the predator decoy to examine how herbivorous fishes reconcile the conflicting demands of avoiding predation vs. foraging within a reefscape context. We show that with increasing risk, herbivorous fishes consumed dramatically less food (ca. 90%) but fed at a faster rate when they did feed (ca. 26%). Furthermore, we show that fishes foraging closest to the predator decoy were 40% smaller than those that foraged at further distances. Thus, smaller individuals showed muted response to predation risk compared to their larger counterparts, potentially due to their decreased risk to predation or lower reproductive value (i.e. the asset protection principle). Habitat heterogeneity mediated risk effects differently for different species of herbivores, with predation risk more strongly suppressing herbivore feeding in more complex areas and for individuals at higher risk of predation. Predators appear to create a reefscape of fear that changes the size structure of herbivores towards smaller individuals, increases individual feeding rates, but suppresses overall amounts of primary producers consumed, potentially altering patterns of herbivory, an ecosystem process critical for healthy coral reefs.
Journal of Animal Ecology - Tập 85 Số 1 - Trang 146-156 - 2016
Abiotic factors control invasion by Argentine ants at the community scale Summary
A prominent and unresolved question in ecology concerns why communities differ in their susceptibility to invasion. While studies often emphasize biotic resistance, it is less widely appreciated how the physical environment affects community vulnerability to invasion. In this study we performed field experiments to test how abiotic variation directly and indirectly influences the extent to which Linepithema humile Mayr (Argentine ants) invade seasonally dry environments in southern California. In controlled and replicated experiments involving drip irrigation, we demonstrate (i) that elevated levels of soil moisture increased both the abundance of Argentine ants and their ability to invade native ant communities and (ii) that cessation of irrigation caused declines in the abundance of Argentine ants and led to their withdrawal from previously occupied areas. Because drip irrigation stimulated plant growth, in an additional experiment we manipulated both soil moisture and plant cover to assess the direct vs. indirect effects of added water on the abundance of L. humile . Local abundance of Argentine ants increased in irrigated plots but was 38% higher in irrigated plots with plants compared to irrigated plots where plant growth was suppressed. The results of this experiment thus argue for a direct role of soil moisture in influencing Argentine ant abundance but suggest that that the indirect effects of added water may also be important. Our study illustrates more generally that fine‐scale variation in the physical environment can control whether communities become invaded by non‐native species and suggests that an understanding of community susceptibility to invasion will be improved by a better appreciation of interactions between the biotic and abiotic environment.
Journal of Animal Ecology - Tập 75 Số 2 - Trang 368-376 - 2006
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