Abstract
It is generally accepted that organisms that naturally exploit an ecosystem facilitate coexistence, at least partially, through resource partitioning. Resource availability is, however, highly variable in space and time and as such the extent of resource partitioning must be somewhat dependent on availability. Here we test aspects of resource partitioning at the inter- and intra-specific level, in relation to resource availability in an atypical aquatic environment using an isotope approach. Using closely related key organisms from an ephemeral pond, we test for differences in isotopic signatures between two species of copepod and between sexes within each species, in relation to heterogeneity of basal food resources over the course of the ponds hydroperiod. We show that basal food resource heterogeneity increases over time initially, and then decreases towards the end of the hydroperiod, reflective of the expected evolution of trophic complexity for these systems. Resource partitioning also varied between species and sexes, over the hydroperiod with intra- and inter-specific specialisation relating to resource availability. Intra-specific specialisation was particularly evident in the omnivorous copepod species. Our findings imply that trophic specialisation at both the intra- and inter-specific level is partly driven by basal food resource availability.
Highlights
Water chemistry[16], and with associated changes in basal food resources
We postulate that the key copepod species, Lovenula raynerae and P. lamellatus will exhibit predictable dietary shifts over the course of a ponds hydroperiod
We hypothesise that (1.) at the early stages of a ponds hydroperiod, males and females of both species would have large dietary niche overlaps given the low overall trophic complexity within these systems at this stage, (2.) with an increase in pond age, an increase in intra- and interspecific feeding specialisation will be observed and (3.) at the end of a ponds hydroperiod, known reductions in trophic complexity would once more result in intra- and inter-specific homogenisation of trophic niches for male and female L. raynerae and P. lamellatus. These hypotheses were tested on a natural plankton community using an isotope approach, whereby the isotopic mixing space of the planktonic food web were determined at four discrete periods over the course of an ephemeral pond’s hydroperiod, in relation to the trophic niche space of male and female L. raynerae and P. lamellatus
Summary
Water chemistry[16], and with associated changes in basal food resources. The present study focusses on two such species and addresses the question of whether these organisms vary food resource exploitation as a result of the rapidly changing environment in which they reside. We hypothesise that (1.) at the early stages of a ponds hydroperiod, males and females of both species would have large dietary niche overlaps given the low overall trophic complexity within these systems at this stage, (2.) with an increase in pond age, an increase in intra- and interspecific feeding specialisation will be observed and (3.) at the end of a ponds hydroperiod, known reductions in trophic complexity would once more result in intra- and inter-specific homogenisation of trophic niches for male and female L. raynerae and P. lamellatus These hypotheses were tested on a natural plankton community using an isotope approach, whereby the isotopic mixing space of the planktonic food web were determined at four discrete periods over the course of an ephemeral pond’s hydroperiod, in relation to the trophic niche space of male and female L. raynerae and P. lamellatus
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