ASSESSMENT OF NICHE PARTITIONING IN CO-OCCURRING SILVERSIDES FROM THE ALBEMARLE AND PAMLICO SOUNDS OF NORTH CAROLINA
Cope, W. Robert
The niche partitioning hypothesis predicts that two species cannot compete for the same limited resources and that one species should differentiate (genetically, morphologically or behaviorally), so that the two species are filling separate niches. To test this hypothesis, we collected two co-occurring silverside species, the Atlantic silverside Menidia menidia and Inland silverside Menidia beryllina, from the Albemarle and Pamlico Sounds of North Carolina. Approximately 1,100 fish were collected through multiple beach seining trips from 20 sites in the Pamlico Sound and 8 sites from the Albemarle Sound throughout the months of August to November of 2013. The fish from each site were positively identified as being Menidia menidia or Menidia beryllina and their total length was measured (to the nearest mm). Length frequency analysis showed that M. menidia were larger at any given time than M. beryllina in both bodies of water. Food habit analysis showed that silversides in the Albemarle Sound were preying upon dipteran insects and chironomid larvae while silversides in the Pamlico Sound were preying upon copepods. Niche overlap analysis was run using a Pianka Index in EcosimR. Index analysis showed high overlap values between M. menidia and M. beryllina in both the Albemarle and Pamlico Sounds. These data do not support the niche partitioning hypothesis. It is possible that when food availability changes and becomes limited, overlap in diet may change as well, increasing food competition. More data (including food availability data and diet analyses during additional time periods or years) are needed to confirm results.