Habitat use is linked to resource‐specific performance of an ecologically important marsh predator

Abstract

It is commonly assumed that animals should preferentially use habitats that enhance their individual performance. However, there have been few attempts to empirically test the relationship between an animals’ habitat use and performance. This is surprising, since knowing about this connection should enhance our ability to predict the local population dynamics of ecologically important species. Here, we used three primary experiments to assess the relationship between habitat use and performance for an important insect consumer (ladybeetles). First, we used field manipulations of resource availability (i.e., scale insects and cordgrass pollen) to examine the habitat use of ladybeetle predators. Second, we conducted a series of no‐choice laboratory assays to compare the performance (fecundity and longevity) of ladybeetles on these different resources. Third, we quantified adult ladybeetle preference for olfactory cues from cordgrass with and without scale insects using a Y‐tube olfactometer. In the field, adult ladybeetles selectively used plots containing scale insects. In the laboratory, diets containing scale insects maximized both adult and larval ladybeetle longevity, and adult fecundity. Adult ladybeetles were attracted to chemical cues associated with scale insects over distances of 10s of centimeters. Overall, our findings suggest that the habitat use and performance of ladybeetles are strongly linked, with ladybeetles preferentially using habitats that maximize their individual performance.

Conspecifics, not pollen, reduce omnivore prey consumption

“…We used this ladybeetle-scale insect model system for three reasons. First, ladybeetles in this system are facultative omnivores, as access to cordgrass pollen facilitates ladybeetle survival in the absence of other dietary resources [18]. Specifically, adult ladybeetles provided only access to cordgrass pollen survived 1.97-times longer than ladybeetles provided access to no food resources.…”

“…In contrast, omnivore prey consumption may increase in the presence of plant resources if these resources increase the local abundance of omnivores through a numerical response (i.e. aggregation and enhanced fitness) [5, 15–18] or by lengthening omnivore persistence in habitats with low prey densities [1, 17, 19–21]. For instance, habitat patches containing high densities of lima bean pods had larger populations of omnivorous big-eyed bugs ( G .…”

“…Here, we assessed how pollen and conspecific density affect the foraging behavior of an omnivorous salt marsh ladybeetle ( Naemia seriata ) feeding on scale insects ( Haliaspis spartinae ). Ladybeetles in this system commonly consume over 100 scale insects per week (per capita) and can reach densities of 10–16 adult ladybeetles per 0.25m 2 [18, 28]. We used laboratory mesocosms to assess the impacts of pollen [i.e.…”

Conspecifics, not plant reproductive tissues, reduce omnivore prey consumption

“…This suggests that in the absence of other prey resources, adult ladybeetles likely consume cordgrass pollen to promote their longevity. Second, adult ladybeetles show resource-dependent aggregation in the field, with ladybeetles tending to preferentially aggregate to habitats containing both scale insects and cordgrass flowers over habitats lacking these resources [18]. Third, adult ladybeetles often aggregate with conspecifics on cordgrass flowers (S. Rinehart and J.D.…”

“…In contrast, omnivore prey consumption may increase in the presence of PRTs if these resources increase the local abundance of omnivores through a numerical response (i.e. aggregation and enhanced fitness) [5, 15-18] or by lengthening omnivore persistence in habitats with low prey densities [1, 17, 19-21]. For instance, habitat patches containing high densities of PRTs (lima bean pods) had larger populations of omnivores and omnivores were less-likely to emigrate from patches containing lima bean pods [17].…”