Niche partitioning in an assemblage of granivorous rodents, and the challenge of community-level conservation
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Coexistence of competing species in the same foraging guild has long puzzled ecologists. In particular, how do small subordinate species persist with larger dominant competitors? This question becomes particularly important when conservation interventions, such as reintroduction or translocation, become necessary for the smaller species. Exclusion of dominant competitors might be necessary to establish populations of some endangered species. Ultimately, however, the goal should be to conserve whole communities. Determining how subordinate species escape competitive exclusion in intact communities could inform conservation decisions by clarifying the ecological conditions and processes required for coexistence at local or regional scales. We tested for spatial and temporal partitioning among six species of native, granivorous rodents using null models, and characterized the microhabitat of each species using resource-selection models. We found that the species' nightly activity patterns are aggregated temporally but segregated spatially. As expected, we found clear evidence that the larger-bodied kangaroo rats drive spatial partitioning, but we also found species-specific microhabitat associations, which suggests that habitat heterogeneity is part of what enables these species to coexist. Restoration of natural disturbance regimes that create habitat heterogeneity, and selection of translocation sites without specific competitors, are among the management recommendations to consider in this case. More generally, this study highlights the need for a community-level approach to conservation and the usefulness of basic ecological data for guiding management decisions.Keywords:
Guild
Competitor analysis
Niche differentiation
Ecological release
Umbrella species
Robinia
Ecological release
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A species-addition experiment showed that prairie grasslands have a structured, nonneutral assembly process in which resident species inhibit, via resource consumption, the establishment and growth of species with similar resource use patterns and in which the success of invaders decreases as diversity increases. In our experiment, species in each of four functional guilds were introduced, as seed, into 147 prairie–grassland plots that previously had been established and maintained to have different compositions and diversities. Established species most strongly inhibited introduced species from their own functional guild. Introduced species attained lower abundances when functionally similar species were abundant and when established species left lower levels of resources unconsumed, which occurred at lower species richness. Residents of the C4 grass functional guild, the dominant guild in nearby native grasslands, reduced the major limiting resource, soil nitrate, to the lowest levels in midsummer and exhibited the greatest inhibitory effect on introduced species. This simple mechanism of greater competitive inhibition of invaders that are similar to established abundant species could, in theory, explain many of the patterns observed in plant communities.
Guild
Niche differentiation
Limiting
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集团结构和生态位特征是量化动物群落组织过程的重要指标，鸟类集团结构及其食物资源分割的分析对于理解群落中不同鸟种生态适应性具有重要意义.越冬水鸟集团结构和生态位特征取决于食物资源的丰富度和可获得性.本文通过对升金湖越冬水鸟的觅食生境和觅食行为的观察，对水鸟群落的集团结构进行划分，采用Levins指数和Pianka指数计算生态位宽度和生态位重叠度.结果表明，升金湖越冬水鸟可被划分为4个觅食集团，即G1浅水啄食集团、G2草滩啄食集团、G3广食性集团和G4深水潜水觅食集团.在浅水和中水区的觅食集团物种组成比深水区的水鸟集团丰富.G3广食性集团的生态位宽度远高于其余3个特化集团.比较而言，所有水鸟物种的觅食行为均较特化，但在觅食生境方面却较宽化.同一集团内物种间的生态位重叠远高于集团间的生态位重叠.G3广食性集团内物种的生态位重叠度低于其它特化集团内物种的生态位重叠度.研究结果表明，升金湖越冬水鸟群落集团结构主要受食物资源空间配置及其可利用性的影响.水鸟群落结构和生态位特征的信息对监测升金湖湿地的质量和制定有效的湿地保护策略都具有重要意义.;Guild structure and niche characteristics are important indicators to quantify the assemble process of animal community. It is of great significance to analysis bird guild structure and food resource partitioning for understanding ecological adaptability of different bird species in a community. The guild structure and niche characteristics of wintering waterbirds depend on the abundance and availability of food resources. In this study we divided the guild structure of waterbird community based on the data of foraging habitat and foraging behavior of wintering waterbirds collected at Lake Shengjin, and calculated the niche width and niche overlap using Levin's index and Pianka index. The results showed that the waterbirds at Lake Shengjin can be divided into four different foraging guilds, namely the G1, pickers in shallow-water, G2, pickers in grassland, G3, generalists and G4, divers. The species composition of foraging guilds in shallow and middle-depth water is richer than that in deep water. The niche width of G3 generalists is much higher than that of the other three specialized species guilds. In comparison, the foraging behavior of all waterbird species is more specialized, but the foraging habitat is more generalized. The niche intra-guild overlap of waterbird species is much higher than that of inter-guilds. The niche overlap of species in G3 generalist is lower than that in other specialized guilds. The results show that the guild structure of wintering waterbird community at Lake Shengjin mainly affected by the spatial allocation and availability of food resources. The information of water bird community structure and niche characteristics is of great significance for monitoring the quality of Lake Shengjin wetland and developing effective wetland protection strategies.
Guild
Optimal foraging theory
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Ecological release
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Plant communities on tropical high islands, such as the Hawaiian Islands, are predicted to experience rapid climate change, resulting in novel climates. If increased temperature and/or drought exceed plant species' current tolerances, species that are unable to adapt or shift ranges risk extinction. By definition, habitat generalists have a wide niche breadth and thrive in a variety of habitats, whereas habitat specialists have a narrow niche breadth, and typically thrive under more specific climatic characteristics (e.g., cold). The objectives of this study were to: (1) classify plant species in the Hawaiian Islands along a habitat generalist-specialist continuum; (2) independently test the validity of species rankings, using environmental and biogeographic ranges; and (3) identify species' life-history traits that predict species location along the continuum. We quantified specialization for 170 plant species using species co-occurrence data from over one thousand plots to rank species' realized habitat niche breadth using the Jaccard index. The distribution of species along this continuum differed by species biogeographic origin, with endemic plant species ranked on the specialist end and non-native plant species ranked on the generalist end. Habitat specialization rankings also differed for four of nine tested variables (while controlling for biogeographic origin): number of habitat moisture types, minimum elevation, number of Hawaiian Islands, and life form. Life form was the only trait tested that differed across the continuum, with woody species ranked as stronger generalists than herbaceous species; this pattern was particularly evident for non-native species. This indirect method of estimating species' potential climatic flexibility uses increasingly available large plant community data sets with output rankings which represent species' realized habitat niches. Identifying species and plant communities that are on the habitat specialist end of the continuum allows for their prioritization in conservation planning, as globally the loss of specialists is an indication of degradation.
Species distribution
Ecological release
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Individuals from habitat generalist species are often thought to be habitat generalist themselves, but this assumption should be examined in light of mounting evidence for native and phenotypic habitat preference. We experimentally tested whether the White-throated Sparrow ( Zonotrichia albicollis (Gmelin, 1789)) exhibits habitat preferences at the individual level. The White-throated Sparrow was a habitat generalist species in our study area, with high occupancy of clearcuts as well as mature forests. However, males in mature forests whose territories were clear-cut in the winter following their breeding season (n = 14), dispersed twice as far as males from uncut mature forests (n = 21). New territories selected by males after clearcuts contained significantly more mature forest than what remained in the territory that they abandoned, but not as much mature forest as was found in their former territory. Gain in uncut habitat after dispersal was positively correlated with dispersal distance. Clear-cut locations left vacant by dispersing males were colonized by new conspecifics. Our results suggest that individual sparrows use only a subset of their species’ wide range of habitats. We question the assumption that individuals from a generalist species are versatile and unlikely to be affected by habitat disturbance.
Home range
Ecological release
Occupancy
Emberizidae
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Biological invasions represent a fascinating process with potentially severe consequences, as the displacement of native species. Therefore, determining the impact on natives and the whole ecosystem is inevitable to protect the endemic biodiversity. At the Lower Rhine a special situation has arisen from three congeneric fish species of the family Gobiidae establishing populations with high densities in a strongly anthropogenic altered habitat, which is additionally limited in dietary resources. Mechanisms of niche separation for the three goby species could be shown on a spatial and temporal axis. Although high dietary overlaps were obtained between the three goby species, ontogenetic dietary shifts in combination with habitat shifts reduced levels of competition. Fine-tuned niche differentiation was also displayed in reproductive traits by temporal separation of spawning onset and intensity, as well as in drifting patterns. Drifting strategy differed within the three species not only to their temporal occurrence in the drift, but also regarding the sizes of drifting individuals. These mechanisms of niche partitioning were suggested to allow for the co-existence of the three Gobiidae and to enforce the impact on native species. The system seemed to have reached its capacities, as already decreasing densities of bighead goby and high levels of dietary competition indicate. Competitive and predatory interactions emerged between the single goby species, as well as with the native fish community. A temporal scaled bottom-up top-down system could be obtained for invasive gobies and two native Percidae. Native piscivores were forced into a dietary juvenile competitive bottleneck, while later on preying on gobies. Adaptation to this novel prey has just started, thus up to now detrimental effects of the competitive interactions prevail. Additionally, population development of the three invasive species is still in progress, revealing a highly dynamic system, where the next years will determine the outcome of this invasion.
Ecological release
Niche differentiation
Round goby
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Abstract Niche partitioning among close relatives may reflect trade‐offs underlying species divergence and coexistence (e.g., between stress tolerance and competitive ability). We quantified the effects of habitat and congeneric species interactions on fitness for two closely related herbaceous plant species, Mimulus guttatus and Mimulus laciniatus , in three common habitat types within their sympatric range. Drought stress strongly reduced survival of M. guttatus in fast‐drying seeps occupied by M. laciniatus , suggesting that divergent habitat adaptation maintains this niche boundary. However, neither seedling performance nor congeneric competition explained the absence of M. laciniatus from shady streams where M. guttatus thrives. M. laciniatus may be excluded from this habitat by competition with other species in the community or mature M. guttatus . Species performance and competitive ability were similar in sympatric meadows where plant community stature and the growing season length are intermediate between seeps and streams. Stochastic effects (e.g., dispersal among habitats or temporal variation) may contribute to coexistence in this habitat. Habitat adaptation, species interactions, and stochastic mechanisms influence sympatric distributions for these recently diverged species.
Niche differentiation
Ecological release
Coexistence theory
Local adaptation
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Using species co‐occurrence patterns to quantify relative habitat breadth in terrestrial vertebrates
The breadth of habitats that a species uses may determine its vulnerability to environmental change, with habitat specialists at greater risk than generalists. To test that hypothesis, we need a valid index of habitat specialization. Existing indices require extensive data, or ignore the magnitude of differences among habitat categories. We suggest an index based on patterns of species co‐occurrence within each of the 101 habitat categories recognized by the International Union for Conservation of Nature. Using this metric, a species is allocated a quantitative score based on the diversity of other taxa with which it co‐occurs: a generalist species occurs in a range of habitat categories that vary considerably in species composition, whereas a specialist species is found only in habitats that contain a consistent suite of other species. We provide data on these scores for 22,230 vertebrate species and show that habitat breadth varies among Classes (amphibians > birds > mammals > reptiles). Within each Class, generalist species are less likely to be in decline or threatened with extinction. Because our index is continuous, based on biologically relevant parameters, and easily calculated for a vast number of taxa, its use will facilitate analyses of the evolution and consequences of habitat specialization.
Extinction (optical mineralogy)
Ecological release
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Global biodiversity
Umbrella species
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