Environmental variation, organism-environment feedback and managed populations

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Variability in environmental conditions is an important predictor of population dynamics. Extremes in temperature and moisture conditions often decrease the success of populations. Unfortunately, climate change predictions point to increased variation in environmental conditions. To mitigate negative impacts, organisms often seek out or create habitats with more constant conditions. For example, crayfish create burrows that have more constant temperatures and less variable water levels than the open marsh. Similarly, temperature and humidity under plant canopies may differ substantially from air temperatures, and affect the insects that live there. Within limits, creation of these new habitats could allow species to overcome the negative effects of climate extremes. I propose to develop, test and apply simple predictive models that describe the effects of environmental variability, and organism modification of the physical environment, on invasive, pest, and endangered species. First, I will examine the impact of the variability of good and bad conditions on the probability that non-native species will increase to large density in new locations (i.e. become invasive). While increased variation when mean conditions are too hot is usually very detrimental (i.e. often lethal), variation about cool temperatures can benefit species that prefer warmer climates. Moreover, “runs” of abnormally good conditions can also temporarily increase population density and potentially create large impacts. I will develop models of invasion risk that include these ideas and test them using lab organisms under controlled conditions. I will then determine if these ideas could apply to giant hogweed. This large invasive plant causes skin burns on contact, and so even a temporary increase in the density of this species could have important socio-economic impacts. Second, using pea plants, I will determine how plant shape alters the local environmental conditions under the canopy and affects the aphid pest species that live there. In addition, since plant shape also affects the ability of beneficial insect predators, such as ladybugs, to catch prey, I will develop models to predict which plant shapes aid predators and simultaneously create inhospitable environmental conditions for the prey, so that the pest population is reduced. I will test these predictions in the greenhouse using pea plants, pea aphids and beneficial predators. Such predictions could be used to select crop varieties that have a lower tendency for insect pest outbreaks. Third, I will examine the effect of predator species that modify the environment on their prey. Normally we expect predators to decrease prey populations, but if predators also create beneficial environments, they might actually benefit the prey species. Variability in environmental conditions that determines the frequency of extreme events, such as drought, will determine whether a predator can have a net beneficial impact on its prey. I will develop some general models of this relationship, test them using lab organisms, and then apply these ideas to the management of the endangered Hine's emerald dragonfly. The aquatic larvae of this wetland species are vulnerable to drought, but may take shelter in the burrows of predatory crayfish, which reach down to the water table. Therefore, counterintuitively, a recovery strategy for the endangered dragonfly might require the protection of its known predator. Together these projects will provide theory, experimental tests of theoretical predictions, and applications that may demonstrate the importance of considering both environmental variability and organism-modification of the environment when predicting future population size.