Predator-predator interactions, or “multiple predator effects” (MPEs), are pervasive in the structuring of communities and complicate predictive quantifications of ecosystem dynamics. The nature of MPEs is also context-dependent, manifesting differently among species, prey densities and habitat structures. However, there has hitherto been a lack of consideration for the implications of intraspecific demographic variation within populations for the strength of MPEs. The present study extends MPE concepts to examine intraspecific interactions among male and female predators across differences in prey densities using a functional response approach. Focusing on a copepod-mosquito model predator-prey system, interaction strengths of different sex ratio pairs of Lovenula raynerae were quantified towards larval Culex pipiens complex prey, with observations compared to both additive and substitutive model predictions. Copepods exhibited destabilising Type II functional responses in all treatments, with female copepods significantly more voracious than males under multiple predator groups. Lovenula raynerae exhibited significantly negative MPEs overall which resulted in prey risk reductions. However, whilst not statistically clear, the magnitude of antagonistic interactions subtly differed among predator-predator compositions and prey densities, with female-female antagonisms generally prevalent at low prey densities, and male-male negative interactions greater under high prey densities. Mixed-sex copepod group predation was predicted by both additive and substitutive models, and additive models generated significantly higher consumption estimates than substitutive equivalents given that their predictions were based on the absence of antagonistic non-trophic interactions. We propose the importance of internal population sex demographics as a further context-dependency which influences the nature of MPEs, with demographic implications requiring investigation across other taxonomic and trophic groups.
Bibliographical noteFunding Information:
This study was funded by the Department for the Economy, Northern Ireland. We extend gratitude to Rhodes University for the provision of laboratory facilities. We acknowledge use of infrastructure and equipment provided by the South African Institute for Aquatic Biodiversity (SAIAB) Research Platform and the funding channeled through the National Research Foundation – SAIAB Institutional Support system. This study was partly funded by the National Research Foundation – South African Research Chairs Initiative of the Department of Science and Innovation (Inland Fisheries and Freshwater Ecology, Grant no. 110507 ).
© 2020 Gesellschaft für Ökologie
Copyright 2020 Elsevier B.V., All rights reserved.
- Culex pipiens
- Functional response
- Lovenula raynerae
- Predator-predator interaction
- Sex demographic
- Temporary pond
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics