How Do Differences in Zooplankton Hatching Phenology and the Presence of Predators Affect Population and Ecosystem Level Properties of Aquatic Food Webs?
How Do Differences in Zooplankton Hatching Phenology and the Presence of Predators Affect Population and Ecosystem Level Properties of Aquatic Food Webs?
A growing amount of evidence indicates that both the order in which species enter into a community and the process of predation can play an important role in controlling community dynamics. Seldom considered is how differences in species hatching phenology and predation interact to affect algal resources and growth rates of later arriving species. To investigate these effects we conducted an experiment in mesocosms, where we manipulated the occurrence of different zooplankton species (fairy shrimp, clam shrimp and cladocerans) that differ in hatching phenology andthe presence or absence of predatory Notonecta. We found phytoplankton abundance declined through time at similar rates in all treatments except treatments that contained both fairy shrimp and clam shrimp, where there was little temporal change in the abundance of phytoplankton present. Otherwise the rate of change in phytoplankton abundance through time was similar among treatments, including treatments with no zooplankton, which suggests that each species alone had little influence on phytoplankton abundance. Though periphyton abundance increased through time the rate of change in periphyton abundance was similar across all treatments. The presence of clam shrimp slowed the per capita rate of cladoceran population growth when Notonecta were present but otherwise rates of growth did not vary among treatments. Together these results indicate that species differing in hatching phenology have little influence on ecological systems when alone, but interactions between particular pairs of co-occurring species can have important effects on both population and ecosystem level responses.
Ecological Significance of Sex Ratio Distortion on Parasitoid and Butterfly Populations
Trichogramma kaykai is very small parasitoid of the desert metalmark butterfly Apodemia mormo (Riodinidae) in the Mojave Desert and has been the focal organism for research on the evolutionary ecology of parasitism and sex ratio distorting microbial symbiosis for over three decades. T. kaykai is known to be infected with a unique sex-ratio distorting bacterial parasite in the genus Wolbachia. A central question in the evolutionary ecology of T. kaykai is the extent to which parasitism impacts the ecology of the host butterfly species and the sex ratio of the parasitoid wasp itself. In the summer of 2013 T. kaykai were collected from A. mormo eggs gathered in three sites in Mojave Desert for a ten-year analysis of changes in rates of parasitism and sex ratios. Parasitism rates had increased substantially in two of the three populations. In the third population a parasitoid species replacement appears to taken place within the past ten years. Sex ratio variation associated with Wolbachia infection showed little change in the ten year interval. The effect of Wolbachia-induced sex ratio distortion varied across T. kaykai subpopulations, with significant female-biased distortion observed in some, but not other populations. The impact of Wolbachia infection on rates of parasitism and sex allocation are discussed in the context of long-term analysis of the evolutionary ecology of this unique tripartite parasitic interaction.
Increasingly researchers acknowledge that non-consumptive predator-prey interactions can have profound effects. We propose that coyote (Canis latrans) effects on white-tailed deer (Odocoiles virginianus) may transcend direct mortality and that the non-consumptive interactions and their implications for deer populations and habitats should be investigated. We used a combination of monitoring data and experimentation to evaluate the potential for non-consumptive effects of coyotes on deer nutritional condition, reproductive strategy, and herbivory patterns on the Jones Ecological Research Center, in southwestern Georgia. We predicted harvest weights of 466 adult does from an 11 year period, and using an information theoretic approach we found support for the effects of predation risk (β=-1.42+0.69) and individual attributes (i.e., age [β=-1.44+0.31], evidence of lactation [β=-1.11+0.55]), but not resource availability. To evaluate the effects of predation risk on reproductive fitness we measured ovulations rates of does during a coyote decline. We found that during low coyote abundance, ovulation rates (1.5 CL/female deer) were 1.7 times greater than during high coyote abundance (0.9 CL/female deer, P = 0.03), despite increased deer abundance and similar nutritional condition. Increased recruitment was better explained by ovulation rates than survival rates of marked fawns. We previously demonstrated predator exclusion influenced deer foraging and therefore we measured the abundance of 10 selected browse species in predator exclosures and controls. Selected browse species were 1.3 times more abundant in controls (P=0.009). We suggest coyotes may have substantial non-consumptive effects on deer and their habitats in the Southeast, and that future research should investigate these interactions.
1 University of Georgia; 2 Joseph W. Jones Ecological Research Center
61 • Meredith Campbell1, Lawrence E. Hurd1, Pieter A. P. deHart2, Joseph M. Taylor1
