Direct and indirect effects of the guppy, Poecilia reticulata, on the structure and function of stream ecosystems in the northern range mountains of Trinidad
Simon, Troy Nathaniel
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We are currently in the middle of the sixth mass extinction, thus predicting the ecological consequences of species loss from communities is a high priority research topic. Additionally, characterizing the ecosystem impact of macroconsumers has strong conservation implications, given the global trend in biodiversity loss toward higher trophic levels. The goal of this dissertation was to use Trinidadian guppies in the mountain streams of Northern Trinidad as a model system to explore several potentially important direct and indirect ecosystem effects of macroconsumers, which we have little understanding of in natural systems. This collection of studies utilizes both localized exclusion of macroconsumers using underwater electric fences within pools, as well as the natural reach-scale exclusion of guppies above and below barrier waterfalls to examine the ecosystem-level effects of macroconsumers. Results show that local adaptation of guppy populations, to the absence of large piscivores in higher elevation streams, shifted their top-down effects from reducing macroinvertebrate standing stock biomass, to reducing primary producer standing stock biomass. Additionally, the consumptive and non-consumptive effects guppies had similar but opposing effects on algal growth and biomass, which resulted in strong treatment effects from excluding guppies on primary algae. Finally, the loss of omnivorous guppies from a macroconsumer assemblage can alter the strength of top down effects of the remaining macroconsumer community on an important ecosystem-level process at both local- and landscape-scales. Together these studies expand our understanding of how macroconsumers alter ecosystem-level processes in natural systems.