The importance of host plant limitation for caterpillars of an arctiid moth (Platyprepia virginalis) varies spatially

Abstract

Spatial dynamic theories such as source-sink models frequently describe habitat-specific demographies, yet there are surprisingly few field studies that have examined how and why interacting species vary in their dynamics across multiple habitat types. We studied the spatial pattern of interaction between a chewing herbivore and its primary larval host plant in two habitat types. We found that the interaction between an arctiid caterpillar (Platyprepia virginalis) and its host (Lupinus arboreus) differed in wet vs. upland dry habitats, as did yearly population dynamics for the caterpillar. In upland sites, there was a strong positive relationship between lupine cover and the abundance of caterpillars although this relationship was not apparent in wet sites. Additionally, in wet sites, caterpillar populations were larger and less variable across years. Caterpillars appeared to exhibit source-sink dynamics, with the time-averaged finite growth rate lamda > 1 in wet sites (sources), lamda < 1 in upland dry sites (sinks), and predominant source-to-sink movement of late-instar caterpillars. Populations in upland dry sites also went locally extinct in years of low regional abundance. Emigration from wet sites could potentially explain the lack of coupling of herbivore and host plant dynamics in these sites. These results indicate that movement and other factors affecting demography are habitat-specific and have important implications for trophic control. Acknowledging such complexity makes simple models of trophic control seem overly general but may allow us to formulate more broadly applicable ecological models.

Predation and associational refuge drive ontogenetic niche shifts in an arctiid caterpillar

“…During preliminary surveys, we found all P. virginalis cocoons in prairie habitat, which is also consistent with previous work indicating that prepupating caterpillars shifted from marsh to prairie habitat (Karban et al 2012). An unexpected finding of the survey, however, was that the majority of cocoons were located on thistle species and none were found on bush lupine (Lupinus arboreus), the primary larval host plant at our study site.…”

Wet years have more caterpillars: interacting roles of plant litter and predation by ants

“…Caterpillars were more abundant following wet winters (Karban and de Valpine ) and at wet sites (Karban et al. ). The relationship between precipitation and caterpillar numbers was improved when we considered the number of large rainfall events rather than the total seasonal accumulation (Fig.…”

“…Population dynamics also varied spatially; wet sites had more caterpillars and tended to have positive population growth in most years while dry sites acted as population sinks in most years and were prone to local extinction (Karban et al. ).…”

Non‐trophic effects of litter reduce ant predation and determine caterpillar survival and distribution

“…They never completely defoliate lupine bushes although it is possible that litter becomes limiting to early instars or that food quality rather than quantity becomes important. Caterpillar densities were correlated with lupine cover at dry sites with low caterpillar densities but were unrelated with lupine cover at wet sites that produce most of the caterpillars (Karban et al 2012b). As such, host‐plant abundance was not a limiting factor for caterpillar populations.…”