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 ...»»»»
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 My´vatn, 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 My´vatn (.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.^^^^