Abstract
Spatial patterns in the abundance of species are determined by local abiotic and biotic conditions, and by the movement of individuals among localities. For species distributed among discrete habitat “islands”, such as zooplankton distributed among lakes, local conditions within lakes often dominate low movement rates among lakes to determine the composition of communities. Here, we ask whether the same abiotic and biotic environmental conditions can generate spatial patterns in the distribution of zooplankton within a lake where there are high horizontal movement rates. We conducted three spatial surveys of zooplankton communities in Lake Mývatn, Iceland, a moderately sized (37 km2) shallow lake with a high outflow rate. The pelagic zooplankton community showed strong spatial structure (spatial autocorrelation), with species composition varying with spatial variation in chlorophyll‐a, the abundance of Anabaena (cyanobacteria), lake depth, light extinction coefficient, and temperature. These factors are known from other studies to be strong drivers of among‐lake variation in freshwater zooplankton communities. However, in contrast with among‐lake studies, fish (stickleback) abundance had no measureable effect on the abundance or species composition of the zooplankton community, although high local stickleback abundance was associated with low zooplankton:phytoplankton biomass ratios. Finally, a parallel study of the underlying benthic crustacean community showed much finer spatial variation (spatial autocorrelation to a range ≤0.6 km vs. 9 km for pelagic zooplankton), suggesting that the stationary character of the benthos allows finer grained spatial patterns. Given the high flow rate of water in Mývatn (>200 m/d), the generation of spatial patterns suggests very strong effects of variation in abiotic and biotic environmental conditions on the population dynamics of zooplankton in the lake.
Highlights
Understanding spatial patterns in the abundance of species and the composition of communities is a well-established goal in ecology (Clements 1916, Gleason 1926, Whittaker 1956)
Evidence points to bottom-up forces determining the composition of the zooplankton community
Sites with lower phytoplankton biomass had higher zooplankton biomass, with these sites dominated by D. longispina and C. abyssorum
Summary
Understanding spatial patterns in the abundance of species and the composition of communities is a well-established goal in ecology (Clements 1916, Gleason 1926, Whittaker 1956). The main drivers of spatial patterns are generally thought to consist of factors affecting movement within lakes, such as wind-induced water currents and immediate weather conditions (Jones et al 1995, Pinel-Alloul et al 1999, George and Winfield 2000, Thackeray et al 2004, Rinke et al 2009) It is possible for sufficiently strong abiotic and/or biotic gradients to generate spatial patterns in zooplankton composition within large lakes or among isolated basins (Stansfield et al 1997, Pinel-Alloul et al 1999, Levesque et al 2010, Davidson et al 2011, 2013). Whether spatial gradients in environmental factors can drive large differences in abundance and community composition in smaller wellmixed lakes, has not been shown
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