Species differences in environmental preferences are some of the most striking aspects of natural history. These differences are often hypothesized to maintain diversity, particularly when they occur in reproduction or recruitment. However, to affect diversity maintenance these differences must mediate density feedbacks. The necessary connection between species differences and density feedbacks may not be straightforward in organisms with multi-stage life cycles.
Hydrobiosid caddisflies, like many insects, have oviposition preferences that differ among species, yielding different distributions of egg masses over emergent rocks in fast-flowing streams. Oviposition differences potentially alter density-dependent interactions in the egg stage itself and in the larval stage by controlling the spatial distribution of larvae in the benthic environment. We use coexistence theory and numerical models to investigate caddisfly life history, focusing on the potential for oviposition differences to maintain diversity when density feedbacks occur in different life stages.
Differences in oviposition preferences, and the resulting differences in egg and larval distributions, can promote coexistence in caddisfly communities. The outcome depends on the stage in which density-dependence occurs and is mediated by other life history. For example, if density-dependent mechanisms act in the egg stage, such as disease, the necessary feedbacks can be direct and strong. Density-dependent interactions in the larval stage, e.g. competition for food, can also support coexistence from oviposition differences. This support tends to be weaker because intervening life history, such as larval dispersal, undermines the connection between oviposition differences and larval density patterns.
By using coexistence theory to investigate oviposition characteristics in caddisflies, we identify the situations where differences in oviposition preferences might affect caddisfly diversity. We illustrate that the stage in which density dependence occurs influences the outcome. Our findings generalise to many other multi-stage organisms and demonstrates the utility of using coexistence theory to probe the implications of empirically-interesting life-history characteristics.