The interaction between space and time travel on the assembly of zooplankton communities

Background/Question/Methods

The colonization of habitats via dispersal is a critical process generating biodiversity within ecological systems.  In addition to dispersing in space, individuals of many species can also disperse through time by producing dormant stages that persist as natural archives of prior populations.  For example, zooplankton produce dormant eggs that accumulate in pond sediment and both active and dormant life stages can spatially disperse via wind and animal vectors. Although many have investigated how spatially dispersing organisms affect community structure, less work has examined the combined influence of spatial and temporal dispersal on the development of ecological communities. We examined how spatial dispersal of zooplankton from a natural source pond affected the development of a zooplankton community in artificial ponds that either contained, or did not contain, a zooplankton egg bank.  We expected temporal dispersal from dormant egg banks would weaken the effect of spatial dispersal, because the presence of an existing community would likely reduce the successful colonization of spatially dispersing individuals.  Alternatively, we also recognized that rapid rates of spatial dispersal could weaken the influence of temporal dispersal if emergence from the egg bank was slow enough that the resident zooplankton community did not adversely affect newly arriving colonists. 

Results/Conclusions

We found that differences in spatial and temporal dispersal had no effect on the number of species present in a pond.  Nonetheless, both spatial and temporal dispersal affected the total abundance and species composition of zooplankton present, but their effects were interdependent.  Specifically, temporal dispersal had no effect when spatial dispersal was high, but greatly altered total zooplankton abundance and species composition when spatial dispersal was low.  Higher rates of spatial dispersal increased total zooplankton abundance when temporal dispersal was absent, but did not affect zooplankton abundance when a dormant egg bank was present.  Our results indicate that changes in the rates of either form of dispersal into a pond could have important consequences for the zooplankton assemblage present.  Depending on the degree of isolation of the ponds, temporal dispersal may have a greater role in species persistence than spatial dispersal.  Yet, when an egg bank is absent, such as in the formation of new ponds, distance from a source pond becomes important.  Understanding aspects of spatial and temporal dispersal and how they interact is critical for restoration efforts after anthropogenic disturbances, since both forms of dispersal allow for re-establishment, thus highlighting the importance of informed management and conservation decisions.