Metacom: An R package for the analysis of metacommunity structure

Metacommunity theory is an extension of metapopulation theory with the goal of understanding how ecological communities vary through space and time. One off-shoot of metacommunity theory deals with understanding how community structure varies along biotic or environmental gradients. The Elements of Metacommunity Structure framework is a three-tiered analysis of metacommunity structure that enables the user to identify metacommunity properties that arise in site-by-species incidence matrices. These properties can then be related to underlying variables that influence species distributions. The EMS framework is now implemented in metacom, an open source R package that allows for the analysis and plotting of metacommunities. © 2014 The Author

Chemical attraction of Dermacentor variabilis ticks parasitic to Peromyscus leucopus based on host body mass and sex

Macroparasites are commonly aggregated on a small subset of a host population. Previous explanations for this aggregation relate to differences in immunocompetence or the degree to which hosts encounter parasites. We propose active tick host choice through chemical attraction as a potential mechanism leading to aggregated tick burdens. We test this hypothesis using a Y-maze olfactometer, comparing chemical attraction responses of larval and nymphal Dermacentor variabilis ticks parasitic to the white-footed mouse, Peromyscus leucopus, as a function of host sex and host body mass. We hypothesized that larger hosts and male hosts would be most attractive to searching ticks, as these hosts commonly have higher tick burdens in the field. Chemical attraction trials were run in the presence and absence of a known tick attractant, host-produced carbon dioxide (CO2). Male hosts and larger hosts were preferred by nymphal D. variabilis in the presence and absence of CO2, whereas larvae had no detectable host preference. The current study suggests that host-produced chemical cues may promote aggregated tick burdens among hosts of a single species based on host body mass and sex. © 2013 Springer Science+Business Media Dordrecht

Co-extinction in a host-parasite network: Identifying key hosts for network stability

Parasites comprise a substantial portion of total biodiversity. Ultimately, this means that host extinction could result in many secondary extinctions of obligate parasites and potentially alter host-parasite network structure. Here, we examined a highly resolved fish-parasite network to determine key hosts responsible for maintaining parasite diversity and network structure (quantified here as nestedness and modularity). We evaluated four possible host extinction orders and compared the resulting co-extinction dynamics to random extinction simulations; including host removal based on estimated extinction risk, parasite species richness and host level contributions to nestedness and modularity. We found that all extinction orders, except the one based on realistic extinction risk, resulted in faster declines in parasite diversity and network structure relative to random biodiversity loss. Further, we determined species-level contributions to network structure were best predicted by parasite species richness and host family. Taken together, we demonstrate that a small proportion of hosts contribute substantially to network structure and that removal of these hosts results in rapid declines in parasite diversity and network structure. As network stability can potentially be inferred through measures of network structure, our findings may provide insight into species traits that confer stability

Relative importance of host environment, transmission potential and host phylogeny to the structure of parasite metacommunities

Identification of mechanisms that shape parasite community and metacommunity structures have important implications to host health, disease transmission, and the understanding of community assembly in general. Using a long-term dataset on parasites from desert rodents, we examined the relative contributions of host traits that represent important aspects of parasite environment, transmission probability between host species, and host phylogeny to the structure of a parasite metacommunity as well as for taxonomically restricted parasite metacommunities (coccidians, ectoparasites and helminths). This was done using a combination of metacommunity analysis and variance partitioning based on canonical correspondence analysis. Coccidian and ectoparasite metacommunities did not exhibit coherent structure. In contrast, helminths and the full parasite metacommunity had Clementsian and quasi-Clementsian structure, respectively, indicating that parasite species distributions for these metacommunities were compartmentalized along a dominant gradient. Variance decomposition indicated that characteristics associated with the host environment consistently explained more variation than did host traits associated with transmission opportunities or host phylogeny, indicating that the host environment is primary in shaping parasite species distributions among host species. Moreover, the importance of different types of host traits in structuring parasite metacommunities was consistent among taxonomic groups (i.e. full metacommunity, coccidians, and helminths) despite manifest differences in emergent structures (i.e. Clementsian, quasi-Clementsian, and random) that arose in response to variation in host environment. © 2014 The Authors

Relative importance of environmental, geographic, and spatial variables on zooplankton metacommunities

© 2014 Dallas and Drake. Understanding the factors responsible for structuring ecological communities is a central goal in community ecology. Previous work has focused on determining the relative roles of two classes of variables (e.g., spatial and environmental) on community composition. However, this approach may ignore the disproportionate impact of variables within classes, and is often confounded by spatial autocorrelation leading to collinearity among variables of different classes. Here, we combine pattern-based metacommunity and machine learning analyses to characterize metacommunity structure of zooplankton from lakes in the northeast United States and to identify environmental, spatial, and geographic covariates associated with metacommunity structure. Analyses were performed for the entire metacommunity and for three zooplankton subsets (cladocerans, copepods, and rotifers), as the variables associated with community structure in these groups were hypothesized to differ. Species distributions of all subsets adhered to an environmental, spatial, and/or geographic gradient, but differed in metacommunity pattern, as copepod species distributions responded independently of one another, while the entire zooplankton metacommunity, cladocerans, and rotifers replaced one another in discrete groups. While environmental variables were nearly always the most important to metacommunity structure, the relative importance of variables differed among zooplankton subsets, suggesting that zooplankton subsets differ in their environmental tolerances and dispersal-limitation