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Model Communities (model + community)

Distribution by Scientific Domains

Life Sciences	80%

Selected Abstracts

When do localized natural enemies increase species richness?

ECOLOGY LETTERS, Issue 4 2005
Frederick R. Adler
Abstract The Janzen,Connell hypothesis states that local species-specific density dependence, mediated through specialist enemies of offspring such as fungal pathogens and insect seed predators, can facilitate coexistence of species by preventing recruitment near conspecific adults. We use spatially explicit simulation models and analytical approximations to evaluate how spatial scales of offspring and enemy dispersal affect species richness. In comparison with model communities in which both offspring and enemies disperse long distances, species richness is substantially decreased when offspring disperse long distances and enemies disperse short distances. In contrast, when both offspring and enemies disperse short distances species richness more than doubles and adults of each species are highly spatially clumped. For the range of conditions typical of tropical forests, locally dispersing specialist enemies may decrease species richness relative to enemies that disperse long distances. In communities where dispersal distances of both offspring and enemies are short, local effects may enhance species richness. [source]

Complexity can enhance stability in competitive systems

ECOLOGY LETTERS, Issue 5 2001
Ian D. Rozdilsky
Empirical observations often indicate that complexity enhances stability, while most theoretical studies, such as May's (1972) classic paper, point to the opposite. Despite the wide generality of these latter theoretical analyses, our examination of the well-known competitive Lotka,Volterra system reveals that increasing complexity (measured in terms of connectance) can enhance species coexistence and persistence in model communities (measured in terms of their feasibility and stability). The high feasibility and stability found for tightly interconnected competitive subsystems might provide an explanation for the clumped structure in food webs. [source]

Species loss leads to community closure

ECOLOGY LETTERS, Issue 6 2000
P. Lundberg
Global extinction of a species is sadly irreversible. At a local scale, however, extinctions may be followed by re-invasion. We here show that this is not necessarily the case and that an ecological community may close its doors for re-invasion of species lost from it. Previous studies of how communities are assembled have shown that there may be rules for that process and that limitations are set to the order by which species are introduced and put together. Instead of focusing on the assembly process we randomly generated simple competitive model communities that were stable and allowed for two to 10 coexisting species. When a randomly selected single species was removed from the community, the cascading species loss was recorded and frequently the resulting community was more than halved. Cascading extinctions have previously been recorded, but we here show that the relative magnitude of the cascade is dependent on community size (and not only trophic structure) and that the reintroduction of the original species lost often is impossible. Hence, species loss does not simply leave a void potentially refilled, but permanently alters the entire community structure and consequently the adaptive landscape for potential re-invaders. [source]

The role of genotypic diversity in determining grassland community structure under constant environmental conditions

JOURNAL OF ECOLOGY, Issue 5 2007
RAJ WHITLOCK
Summary 1A recent experiment varied the genetic diversity of model grassland communities under standardized soil and management conditions and at constant initial species diversity. After 5 years' growth, genetically diverse communities retained more species diversity and became more similar in species composition than genetically impoverished communities. 2Here we present the results of further investigation within this experimental system. We proposed that two mechanisms , the first invoking genetically determined and constant differences in plant phenotypes and the second invoking genotype,environment interactions , could each underpin these results. This mechanistic framework was used as a tool to interpret our findings. 3We used inter-simple sequence repeat (ISSR) DNA markers to confirm which of the individuals of six study species initially included in the model communities were unique genotypes. We then used the molecular markers to assess the survival and abundance of each genotype at the end of the 5-year experimental period. 4The DNA marker data were used to create, for the first time, a genotype abundance hierarchy describing the structure of a community at the level of genotypes. This abundance hierarchy revealed wide variation in the abundance of genotypes within species, and large overlaps in the performance of the genotypes of different species. 5Each genotype achieved a consistent level of abundance within genetically diverse communities, which differed from that attained by other genotypes of the same species. The abundance hierarchy of genotypes within species also showed consistency across communities differing in their initial level of genetic diversity, such that species abundance in genetically impoverished communities could be predicted, in part, by genotypic identity. 6Three species (including two canopy-dominants) experienced shifts in their community-level genotype abundance hierarchies that were consistent with an increased influence of genotype,environment interactions in genetically impoverished communities. 7Our results indicate that under relatively constant environmental conditions the species abundance structure of plant communities can in part be predicted from the genotypic composition of their component populations. Genotype,environment interactions also appear to shape the structure of communities under such conditions, although further experiments are needed to clarify the magnitude and mechanism of these effects. [source]

Covers, volume 25, Number 6, 2009

ANTHROPOLOGY TODAY, Issue 6 2009
Article first published online: 26 NOV 200
Front and back cover caption, volume 25 issue 6 ANTHROPOLOGY IN CHINA In China the history of anthropology is tightly linked to the discovery and documentation of ethnic diversity within the state. The 16th Congress of the International Union of Anthropological and Ethnological Sciences was held in China in summer 2009 in the southwestern state of Yunnan, where this diversity is most pronounced. Participants were encouraged to visit model communities, enjoy music and dance performances by the minorities, and admire their colourful costumes, as in this picture, which shows how VIP guests were welcomed to the closing ceremony of the Congress. Yet just a few weeks earlier, at the other end of the country in Xinjiang, almost 200 people were killed in the worst ethnic rioting since Liberation 60 years ago. While most economic and educational indicators suggest that socialist ethnic policies have been an impressive success, evidently not all is harmonious. Especially among Tibetans and Uyghurs, policies of recognition and the emphasis on a territorial homeland have fostered aspirations which cannot be satisfied by stepping up support for folklore and building ever larger ethnic museums and theme parks. In these regions, the evidence which power holders present as proof of progress and integration, and even as the accomplishment of an ancient civilizing mission, is interpreted locally in terms of assimilation. These tensions constrain the possibilities for anthropological research, for Chinese and foreign scholars alike. In his contribution to this issue, Chris Hann juxtaposes his impressions of the Congress in Kunming with his experiences of rural fieldwork among the Uyghurs of Xinjiang. [source]