Evidence for population level-variability in individual ecological specialization in the Three-spine Stickleback (Gasterosteus aculeatus)

Background/Question/Methods:

Many populations are made up of individual specialists that consistently use only a subset of their species’ niche space. This individual niche variation can influence the intra- and interspecific interactions within a community, potentially changing ecological dynamics.  Despite the ecological importance of individual specialization we know very little about how species that exhibit niche variation vary in their propensity to exhibit individual specialization.  The Three-spine Stickleback (Gasterosteus aculeatus) exhibits great ecological diversity within apparently genetically panmictic populations.  These populations are characterized by continuous, unimodal morphological variation yet individuals show varying degree of ecological specialization on benthic and limnetic resources.  Here we use gut contents (indicating short term diet usage), stable isotopes (indicating long term diet usage), and morphology (traditional measurements and geometric morphometrics) to quantify individual specialization across different lakes and watersheds on northern Vancouver Island.  We also use observations of stickleback foraging to address short-term behavioral consistency in foraging habitat use. 

Results/Conclusions:

While individual specialization seems to be a ubiquitous feature of these populations, the degree of individual dietary specialization varies by population. More morphologically variable populations have higher individual niche variation.  Short term measures of individual specialization calculated with gut contents are correlated with isotopic variation within populations, suggesting the persistence of variability in individual specialization between populations, perhaps driven by morphological variation.  Through a spatially explicit sampling of a single population we find that observed patterns of individual specialization are not driven by sampling design but rather reflect that most diet variability within a population exists at the individual level rather than being driven by spatial isolation.  Behavioral observations indicate that individuals vary in their propensity to utilize different foraging habitat and that this variability is also correlated with stable isotopes measures of diet.   Together, these studies confirm that ecological variability within populations may itself be variable, and that different measures of ecological variability yield congruent inferences.