Non-host Environments Research Articles

Translating Foraging Movements in Heterogeneous Environments into the Spatial Distribution of Foragers

The relationship between movement and population dynamics in heterogeneous environments has been approached from two directions: theoretical analyses using diffusion models and empirical studies that often employ computer simulations. In this paper I am proposing a unified framework for studying individual movements that brings both of these approaches together. The proposed framework is based on the diffusion—approximation" procedure developed by Patlak (1953a, b), which translates a probabilistic description of the pattern of individual movements (such as provided by simulation models) into a partial differential model describing the population redistribution in a patchy habitat. My first goal is this paper was to make Patlak's work accessible to ecologists interested in realistic movement models. Secondly, making some simplifying assumptions I solved Patlick's model to obtain the equilibrium distribution of organisms among patches in a heterogeneous environment. This led me to a definition of "residence index." The residence index of a patch is estimated by observing and recording movement trajectories of organisms within the patch. The pattern of variation in the residence index among different kinds of patches specifies the predicted equilibrium densities of organisms in each patch. I assessed the utility of the above approach by using data on movement tracks of Euphydryas anicia females to calculate butterfly residence indices in host—plant patches vs. nonhost environment. The predicted distribution of butterflies among host and nonhost areas differed by only 16% from the actual distribution, as documented by an independent data set. I also applied the model to data from three studies on insect movement and spatial distribution. The accuracy of model predictions varied from adequate to excellent. Finally, I argue that Patlak's model and its residence—index extension provides a general, and at the same time realistic, framework for quantifying individual movements, and for relating movement patterns to spatial population dynamics. Although this approach, as developed here, is explicitly concerned only with population redistribution within an area, birth/death or immigration/emigration terms can be added in a straightforward manner. Thus, this framework can be very useful in studies of consumer—resource (e.g., predator—prey or herbivore—host) spatial dynamics, since movement behaviors of consumers searching for prey, and prey attempting to avoid consumers, are known to be important in affecting the outcome of such population interactions.

Long-Range Host-Finding Behavior and Colonization of Onion Fields by Delia antiqua (Diptera: Anthomyiidae)

The importance of directed movement by adults of the onion maggot, Delia antiqua (Meigen), in the colonization of new onion fields was assessed. In two mark-recapture experiments where flies were released in the center of circular bands of onions or nonhost vegetation, recaptures of mated females in the host and nonhost circle were distributed randomly. Recaptures of males were distributed randomly in the nonhost circle and directionally in the host circle, either downwind (release 1) or upwind (release 2) of the release point. In six similar releases in two nonhost environments, recaptures of females were randomly distributed regardless of mating status. Recaptures of males were often significantly directional but not correlated with wind direction. Mating status and ovarian development of feral D. antiqua trapped at three sites with different cropping histories were measured. Ovarian development and mating status of flies recaptured in nonhost vegetation 1.2 km from the nearest onion field or overwintering site were similar to those trapped in an onion field. Flies trapped at an overwintering site with no host plants were, on average, younger and less likely to be mated. These results suggest that long-range directed movement has little influence on the probability or extent of colonization of new onion fieldsby D. antiqua .

Survival of microbial plant pathogens in soil

INTRODUCTION The damage done to crop plants by disease-producing organisms has resulted in a more thorough study of the parasitic activity of these organisms than of their saprophytic survival. Yet in the intervals between periods of parasitism these pathogens are most likely to be in a less favorable environment and perhaps more amenable to control. By far the most common non-host environment for these organisms is the soil, which, indeed, is the final resting place for all terrestrial