Ecological and evolutionary effects of stickleback on community structure

Abstract

Species' ecology and evolution can have strong effects on communities. Both may change concurrently when species colonize a new ecosystem. We know little, however, about the combined effects of ecological and evolutionary change on community structure. We simultaneously examined the effects of top-predator ecology and evolution on freshwater community parameters using recently evolved generalist and specialist ecotypes of three-spine stickleback (Gasterosteus aculeatus). We used a mesocosm experiment to directly examine the effects of ecological (fish presence and density) and evolutionary (phenotypic diversity and specialization) factors on community structure at lower trophic levels. We evaluated zooplankton biomass and composition, periphyton and phytoplankton chlorophyll-a concentration, and net primary production among treatments containing different densities and diversities of stickleback. Our results showed that both ecological and evolutionary differences in the top-predator affect different aspects of community structure and composition. Community structure, specifically the abundance of organisms at each trophic level, was affected by stickleback presence and density, whereas composition of zooplankton was influenced by stickleback diversity and specialization. Primary productivity, in terms of chlorophyll-a concentration and net primary production was affected by ecological but not evolutionary factors. Our results stress the importance of concurrently evaluating both changes in density and phenotypic diversity on the structure and composition of communities.

Figure 1. Zooplankton mass in grams per liter across different treatments for (A) crustaceans and (B) rotifers; primary producer abundance in terms of (C) concentration of periphyton and (D) phytoplankton chlorophyll-a concentration in milligrams per liter across treatments and total system net productivity (E) in terms of daily changes in dissolved oxygen concentration in milligrams per liter across treatments.

Bars represent standard error of the mean. Treatments correspond to NF = no fish, G = generalist ecotype, B = benthic ecotype, L = limnetic ecotype, BL = limnetic and benthic ecotype together, BBLL = double density of limnetic and benthic ecotype together.

Figure 2. The first two non-metric multidimensional scaling (NMDS) axes for zooplankton community composition.

Points represent individual tanks, colors represent treatments (NF = no fish, G = generalist ecotype, B = benthic ecotype, L = limnetic ecotype, BL = benthic and limnetic ecotype together, BBLL = double density of benthic and limnetic ecotype together), and polygons surround all tanks of a given treatment. The numbers on each axis correspond to the genera of zooplankton with the strongest loadings (negative and positive). For a graphical representation of the zooplankton genera loadings, please refer to Figure S1.