Community structure in pelagic marine mammals at large spatial scales

摘要

The understanding of a species' niche is fundamental to the concept of ecology, yet relatively little work has been done on niches in pelagic marine mammal communities. Data collection on the distribution and abundance of marine mammals is costly, time consuming and complicated by logistical difficulties. Here we take advantage of a data archive comprising many different datasets on the distribution and abundance of cetaceans from Nova Scotia through the Gulf of Mexico in an effort to uncover community structure at large spatial scales (1000s of km). We constructed a multivariate ordination of the species data, tested for group structure that might exist within the ordination space, and determined how these groups might differ in environmental space. We examined 3 biogeographic regions: the oceanic waters north and south of Cape Hatteras, NC, and the Gulf of Mexico. North of Hatteras, we found 2 main groups split along a temperature and chlorophyll gradient, with most piscivores being found in cooler, more productive waters of the continental shelf, and most teuthivores being found farther offshore in warmer, less productive waters at the shelf break (200 m isobath). South of Hatteras, we found 3 groups, with the largest group being in warmer, lower chlorophyll waters that are closest to shore. In the Gulf of Mexico, we found 7 groups arrayed along a bottom depth gradient. We also tested the effect of taxonomically lumping different beaked whale species on ordination results. Results showed that when beaked whales were identified to the species level, they clustered out into distinct niches that are separate from those of other Odontocete groups. These results add to an increasing understanding of wildlife habitat associations and niche partitionings in the community structure of pelagic species, and provide important baseline information for future population monitoring efforts.