Torres-Campos, I. | Search bioRxiv

bioRxiv2022

Context-dependent effects of temperature and community complexity on trophic interaction strength in a mite community

Both temperature and community complexity are known to affect trophic interaction strength (TIS), but whether their effect is additive or not is as yet an open question. Here we used a 2-predator/3-prey system consistently occurring in avocado orchards to explore the effects of increasing warming and community complexity on the strength of predator:prey trophic interactions. The two predator species differed in their diet breath (a carnivore and an omnivore) and the prey types included a herbivore, heterospecific juvenile predators, and/or pollen. Overall, analyses revealed multiplicative effects of community complexity and both temperature and predator diet breath on the net predator:prey(s) TIS. Indeed, warming led to increased TIS in the community with omnivore as top predator, but only in absence of its preferred food source. When the carnivore was the top predator, in contrast, higher temperatures led to TIS being more negative, but only for the IGprey. We conclude that sources of context dependence in specific systems need to be identified to unveil effects of warming on communities.

ecology↗

bioRxiv2018

The return of the trophic chain: fundamental vs realized interactions in a simple arthropod food web

The mathematical theory describing small assemblages of interacting species (community modules or motifs) has proved to be essential in understanding the emergent properties of ecological communities. These models use differential equations to study pairwise interactions between species. However, as community modules become more complex, it is not certain that all potential interactions will be effectively realized. Here, we use community modules to experimentally explore whether the number of trophic links among species scales with community complexity (i.e., by adding species known to feed on each other from pair-wise trials). To investigate this question, we used a simple mite community present in avocado orchards (Persea americana), composed of two predators (Euseius stipulatus and Neoseiulus californicus), one herbivore as shared prey (Oligonychus perseae), and pollen of Carpobrotus edulis as an alternative food resource. These configurations enabled the potential for (intraguild) predation and (apparent) competition to be expressed. Using a series of controls, we assessed whether the presence of one species affected the survival of another, or its conversion of food into offspring). We found that increasing the number of potential interactions did not result in more complex realized community modules. Instead, all communities were reduced to one or two linear trophic chains. Our results show that trophic links assumed to occur when species are assembled in pairs do not necessarily occur when other components of the community are present. Consequently, food-web structure may be unrealistic in theoretical community modules that are parameterized based on pair-wise interactions observed when alternative prey is absent. This further suggests the need for empirical research to work in concert with theoretical approaches to develop more realistic and predictive food-web models.

ecology↗