The effects of food web structure on ecosystem function exceeds those of precipitation

Abstract

1. Ecosystems are being stressed by climate change, but few studies have tested food web responses to changes in precipitation patterns and the consequences to ecosystem function. Fewer still have considered whether results from one geographic region can be applied to other regions, given the degree of community change over large biogeographic gradients. 2. We assembled, in one field site, three types of macroinvertebrate communities within water-filled bromeliads. Two represented food webs containing both a fast filter feeder-microbial and slow detritivore energy channels found in Costa Rica and Puerto Rico, and one represented the structurally simpler food webs in French Guiana, which only contained the fast filter feeder-microbial channel. We manipulated the amount and distribution of rain entering bromeliads and examined how food web structure mediated ecosystem responses to changes in the quantity and temporal distribution of precipitation. 3. Food web structure affected the survival of functional groups in general and ecosystem functions such as decomposition and the production of fine particulate organic matter. Ecosystem processes were more affected by decreased precipitation than were the abundance of micro-organisms and metazoans. In our experiments, the sensitivity of the ecosystem to precipitation change was primarily revealed in the food web dominated by the single filter feeder-microbial channel because other top-down and bottom-up processes were weak or absent. 4. Our results show stronger effects of food web structure than precipitation change per se on the functioning of bromeliad ecosystems. Consequently, we predict that ecosystem function in bromeliads throughout the Americas will be more sensitive to changes in the distribution of species, rather than to the direct effects caused by changes in precipitation.

Biogeographic context dependence of trophic cascade strength in bromeliad food webs

“…Our results are also consistent with a three‐country community analogue experiment performed in French Guiana bromeliads, in which Costa Rican communities again had higher top‐down control of detritivores compared to Puerto Rican communities because of the difference in top predator identity (Trzcinski et al. ). The lack of bromeliad‐dwelling odonates on the small, isolated island of Puerto Rico suggests dispersal limitation of the few families of odonates that have managed on the mainland to adapt to a bromeliad habitat, giving island biogeography the dominant role in determining top‐down effects in this site.…”

“…S2), corroborating the importance of this family for decomposition (see also Trzcinski et al. ). However, because tipulids were a similar proportion of detritivore biomass in both sites, decomposition was more affected by site differences in total biomass.…”

Environmental drivers of invertebrate population dynamics in Neotropical tank bromeliads

“…Second, the carrying capacity of the system (a major driver of aquatic invertebrate abundance; Spooner & Vaughn, ) was held almost constant both by our sampling scheme (plants were matched by their size) and by bromeliad hydrology. The morphology of tank bromeliads acts as a buffer against variations in precipitations (Trzcinski et al ., ), thus ensuring hydrological stability; here, bromeliads were generally filled to c . 50% of their maximum volume throughout the year.…”

“…Despite their number, ubiquity and wide geographical distribution, tank bromeliads (and plant‐held waters in general) have received relatively little attention in comparison to other freshwater ecosystems. However, recent research driven by interests in medical entomology (some bromeliad‐breeding mosquitoes are vectors of dengue or malaria; Talaga et al ., ), fundamental aspects of phytotelm ecology (Brouard et al ., ; ), or community‐ to ecosystem‐level responses to climate change (Dézerald et al ., ; Trzcinski et al ., ), has started to shed interesting new light on the bromeliad ecosystem structure and function.…”

Effects of predatory ants within and across ecosystems in bromeliad food webs

“…Interestingly, aquatic filter feeders (largely mosquitoes) were not significantly reduced by ants in any site, suggesting that ants may cause a shift from the detritus‐detritivore energy channel in bromeliad food webs to the micro‐organism‐filter feeder energy channel (Trzcinski et al . ). Ants also led to a restructuring of the relative abundances of species in all sites except Cardoso, but the direction of this effect differed between sites.…”