Changes in host–parasitoid food web structure with elevation

Abstract

Summary1. Gradients in elevation are increasingly used to investigate how species respond to changes in local climatic conditions. Whilst many studies have shown elevational patterns in species richness and turnover, little is known about how food web structure is affected by elevation. 2. Contrasting responses of predator and prey species to elevation may lead to changes in food web structure. We investigated how the quantitative structure of a herbivore-parasitoid food web changes with elevation in an Australian subtropical rain forest. 3. On four occasions, spread over 1 year, we hand-collected leaf miners at twelve sites, along three elevational gradients (between 493 m and 1159 m a.s.l). A total of 5030 insects, including 603 parasitoids, were reared, and summary food webs were created for each site. We also carried out a replicated manipulative experiment by translocating an abundant leaf-mining weevil Platynotocis sp., which largely escaped parasitism at high elevations (≥900 m a.s.l.), to lower, warmer elevations, to test if it would experience higher parasitism pressure. 4. We found strong evidence that the environmental change that occurs with increasing elevation affects food web structure. Quantitative measures of generality, vulnerability and interaction evenness decreased significantly with increasing elevation (and decreasing temperature), whilst elevation did not have a significant effect on connectance. Mined plant composition also had a significant effect on generality and vulnerability, but not on interaction evenness. Several relatively abundant species of leaf miner appeared to escape parasitism at higher elevations, but contrary to our prediction, Platynotocis sp. did not experience greater levels of parasitism when translocated to lower elevations. 5. Our study indicates that leaf-mining herbivores and their parasitoids respond differently to environmental conditions imposed by elevation, thus producing structural changes in their food webs. Increasing temperatures and changes in vegetation communities that are likely to result from climate change may have a restructuring effect on host-parasitoid food webs. Our translocation experiment, however, indicated that leaf miners currently escaping parasitism at high elevations may not automatically experience higher parasitism under warmer conditions and future changes in food web structure may depend on the ability of parasitoids to adapt to novel hosts.

Network reorganization and breakdown of an ant–plant protection mutualism with elevation

“…This contrasts with patterns found for seed dispersal and pollinator networks across latitudinal gradients, in which reduced partner availability results in greater specialization [6]. However, decreased specialization with elevation has been observed for leaf miner–parasitoid interaction networks [38]. In contrast with our results, these antagonistic networks showed no change in connectance.…”

Tree phylogenetic diversity promotes host–parasitoid interactions

“…A decline of parasitism towards higher elevations is likely, as the frequency of trophic interactions decreases polewards [59] and local elevation gradients reflect large-scale climatic gradients. To our knowledge, only two recent studies from subtropical Australia have addressed this topic and found a decrease of parasitism with elevation [18,46], which we support. Higher parasitism at lower and warmer lower elevation might be caused by higher attack rates of parasitoids, as demonstrated in controlled warming experiments [60].…”

“…For the system studied and for other host-parasitoid systems (e.g. leaf miner-parasitoid [8,46] or aphid-parasitoid [47]), the biologically most relevant niches are probably food (i.e. food for hosts, hosts of parasitoids; see below) and shelter [4].…”

Can changes in the distribution of lizard species over the past 50 years be attributed to climate change?

“…Environmental temperatures, hibernation length, feeding activity, and food abundance strongly influence lizard distributions (Guisan and Hofer 2003). In particular, food web structure or properties (Albouy et al 2014;Maunsell et al 2015) and the effects of climate warming on biotic interactions will indirectly influence species distributions (Jeffs and Lewis 2013). Most lizard species in our study mainly eat a variety of insects and other invertebrates or a few plant species.…”