Habitat structure, trophic structure and ecosystem function: interactive effects in a bromeliad–insect community

Abstract

Although previous studies have shown that ecosystem functions are aVected by either trophic struc- ture or habitat structure, there has been little consider- ation of their combined eVects. Such interactions may be particularly important in systems where habitat and tro- phic structure covary. I use the aquatic insects in bromel- iads to examine the combined eVects of trophic structure and habitat structure on a key ecosystem function: detri- tal processing. In Costa Rican bromeliads, trophic struc- ture naturally covaries with both habitat complexity and habitat size, precluding any observational analysis of interactions between factors. I therefore designed meso- cosms that allowed each factor to be manipulated sepa- rately. Increases in mesocosm complexity reduced predator (damselXy larva) eYciency, resulting in high detritivore abundances, indirectly increasing detrital pro- cessing rates. However, increased complexity also directly reduced the per capita foraging eYciency of the detritivores. Over short time periods, these trends eVec- tively cancelled each other out in terms of detrital pro- cessing. Over longer time periods, more complex patterns emerged. Increases in mesocosm size also reduced both predator eYciency and detritivore eYciency, leading to no net eVect on detrital processing. In many systems, eco- system functions may be impacted by strong interactions between trophic structure and habitat structure, caution- ing against examining either eVect in isolation.