Biomedical subjects

A R Ives

Publications and source records attributed to A R Ives.

4 recordsLinked to original sources

PubMed2006

Phylogenetic analysis of trophic associations.

Ecologists frequently collect data on the patterns of association between adjacent trophic levels in the form of binary or quantitative food webs. Here, we develop statistical methods to estimate the roles of consumer and resource phylogenies in explaining patterns of consumer-resource association. We use these methods to ask whether closely related consumer species are more likely to attack the same resource species and whether closely related resource species are more likely to be attacked by the same consumer species. We then show how to use estimates of phylogenetic signals to predict novel consumer-resource associations solely from the phylogenetic position of species for which no other (or only partial) data are available. Finally, we show how to combine phylogenetic information with information about species' ecological characteristics and life-history traits to estimate the effects of species traits on consumer-resource associations while accounting for phylogenies. We illustrate these techniques using a food web comprising species of parasitoids, leaf-mining moths, and their host plants.

Animals↗

PubMed2003

Species interactions can explain Taylor's power law for ecological time series.

One of the few generalities in ecology, Taylor's power law, describes the species-specific relationship between the temporal or spatial variance of populations and their mean abundances. For populations experiencing constant per capita environmental variability, the regression of log variance versus log mean abundance gives a line with a slope of 2. Despite this expectation, most species have slopes of less than 2 (refs 2, 3-4), indicating that more abundant populations of a species are relatively less variable than expected on the basis of simple statistical grounds. What causes abundant populations to be less variable has received considerable attention, but an explanation for the generality of this pattern is still lacking. Here we suggest a novel explanation for the scaling of temporal variability in population abundances. Using stochastic simulation and analytical models, we demonstrate how negative interactions among species in a community can produce slopes of Taylor's power law of less than 2, like those observed in real data sets. This result provides an example in which the population dynamics of single species can be understood only in the context of interactions within an ecological community.

Animals↗

PubMed1999

Stability and variability in competitive communities.

Long-term variability in the abundance of populations depends on the sensitivity of species to environmental fluctuations and the amplification of environmental fluctuations by interactions among species. Although competitive interactions and species number may have diverse effects on variability measured at the individual species level, a combination of theoretical analyses shows that these factors have no effect on variability measured at the community level. Therefore, biodiversity may increase community stability by promoting diversity among species in their responses to environmental fluctuations, but increasing the number and strength of competitive interactions has little effect.

Animals↗

PubMed1997

Aggregation and the coexistence of competing parasitoid species.

In nature, many insect species are attacked by more than one specialized species of parasitoid. We examine whether parasitoid aggregation among patches containing hosts can promote the coexistence of specialized parasitoids on the same host species. We construct models to analyze the effects of three types of parasitoid aggregation: direct density-dependent, inverse density-dependent, and density-independent aggregation. All three types of aggregation may facilitate coexistence, provided the parasitoid species show behavioral differences that produce different patterns of aggregation. By deriving general conditions of coexistence of parasitoids, we show that all three types of aggregation act to facilitate coexistence in the same way--by increasing the covariance between the distributions of susceptible hosts and the least common parasitoid. Although they act in the same way, in general the effect of density-independent aggregation in facilitating coexistence is greater than either direct or inverse density-dependent aggregation. This suggests that density-independent aggregation may have the greatest potential to facilitate the coexistence of specialize parasitoids using the same host.

Animals↗