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The way that mothers provision their offspring can have important consequences for their offspring's performance throughout life. Models suggest that maternally induced variation in life histories may have large population dynamical effects, even perhaps driving cycles such as those seen in forest Lepidoptera. The evidence for large maternal influences on population dynamics is unconvincing, principally because of the difficulty of conducting experiments at both the individual and population level. In the soil mite, Sancassania berlesei, we show that there is a trade-off between a female's fecundity and the per-egg provisioning of protein. The mother's position on this trade-off depends on her current food availability and her age. Populations initiated with 250 eggs of different mean sizes showed significant differences in the population dynamics, converging only after three generations. Differences in the growth, maturation and fecundity of the initial cohort caused differences in the competitive environment for the next generation, which, in turn, created differences in their growth and reproduction. Maternal effects in one generation can therefore lead to population dynamical consequences over many generations. Where animals live in environments that are temporally variable, we conjecture that maternal effects could result in long-term dynamical effects.

Predators of herbivorous animals can affect plant populations by altering herbivore density, behavior, or both. To test whether the indirect effect of predators on plants arises from density or behavioral responses in a herbivore population, we experimentally examined the dynamics of terrestrial food chains comprised of old field plants, leaf-chewing grasshoppers, and spider predators in Northeast Connecticut. To separate the effects of predators on herbivore density from the effects on herbivore behavior, we created two classes of spiders: risk spiders that had their feeding mouth parts glued to render them incapable of killing prey and predator spiders that remained unmanipulated. We found that the effect of predators on plants resulted from predator-induced changes in herbivore behavior (shifts in activity time and diet selection) rather than from predator-induced changes in grasshopper density. Neither predator nor risk spiders had a significant effect on grasshopper density relative to a control. This demonstrates that the behavioral response of prey to predators can have a strong impact on the dynamics of terrestrial food chains. The results make a compelling case to examine behavioral as well as density effects in theoretical and empirical research on food chain dynamics

Defences induced against predators fall into three basic categories – behavioural, morphological and life history. Many species induce changes in more than one category. A theoretical advantage of a behavioural change is its potential for rapid induction compared to morphology or life history. We tested this theory by comparing modifications in behaviour and morphology along a time line in the hypotrich ciliate Euplotes octocarinatus exposed to chemical cues from Stenostomum virginianum, a predatory flatworm. Behavioural defences were induced much more rapidly than morphological, although as morphological defences became expressed changes in behaviour were slightly relaxed. This suggests a temporal compensatory relationship between the two traits. Behavioural defences are quickly induced to rapidly reduce predation risk, however they are relaxed as morphology changes are realised to avoid paying the cost of expressing both types of defence.

Many natural enemies do not immediately kill their host, and the lag this creates between attack and host death results in mixed populations of uninfected and infected hosts. Both competition and parasitism are known to be major structuring forces in ecological communities; however, surprisingly little is known about how the competitive nature of infected hosts could affect the survival and dynamics of remaining uninfected host populations. Using a laboratory system comprising the Indian meal moth, Plodia interpunctella, and a solitary koinobiont parasitoid, Venturia canescens, we address this question by conducting replicated competition experiments between the unparasitized and parasitized classes of host larvae. For varying proportions of parasitized host larvae and competitor densities, we consider the effects of competition within (intraclass) and between (interclass) unparasitized and parasitized larvae on the survival, development time, and size of adult moths and parasitoid wasps. The greatest effects were on survival: increased competitor densities reduced survival of both parasitized and unparasitized larvae. However, unparasitized larvae survival, but not parasitized larvae survival, was reduced by increasing interclass competition. To our knowledge, this is the first experimental demonstration of the competitive superiority of parasitized over unparasitized hosts for limiting resources. We discuss possible mechanisms for this phenomenon, why it may have evolved, and its possible influence on the stability of host—parasite dynamics.

Interspecific competition has long been implicated as a force structuring the distribution of organisms along environmental gradients. The research presented here uses a survey, foraging observations, and a manipulative field experiment that test the included-niche competition hypothesis as a mechanism structuring the distribution of a generalist grasshopper, Melanoplus femurrubrum, along a food-resource gradient. A field survey of 10 old fields revealed a step-like reduction in M. femurrubrum abundance as the proportion of grass cover in the fields exceeded 60%. Furthermore, M. femurrubrum abundance and the abundance of a potential competitor, the grass specialist Chorthippus curtipennis, were negatively correlated among the fields. Experimental foraging observations showed that M. femurrubrum was a polyphagous feeder that preferred grass and consumed less grass in the presence of C. curtipennis. The pattern of grasshopper distribution and foraging data support an included-niche competition hypothesis. However, in a field experiment that manipulated C. curtipennis presence and absence and the composition of vegetation in which competition might occur, growth and mortality rates in M. femurrubrum did not respond to C. curtipennis competition. Performance was predicted to be lowest in grass-dominated conditions, those corresponding to the locations where M. femurrubrum does not exist. Instead, growth rates were highest and mortality rates were lowest in grass-only treatments. While the survey and foraging observations support the included-niche hypothesis, the experiments suggest that interspecific competition in adult grasshoppers is not the cause of the grasshopper distribution pattern. Similar experiments in western North American prairies indicate that interspecific competition can be important and that foraging ecology can be a good indicator of the interaction. This study contributes to the increasing body of knowledge about interspecific competition's role in organism distributions. It demonstrates that geographic similarity in natural history need not lead to a similar importance of limiting factors.