Testing the niche width paradigm: How the trophic ecology of consumer communities is influenced by biodiversity

Background/Question/Methods

You are what you eat, and what an organism can eat is the base point in determining its trophic ecology and interactions with other species . The current ecological paradigm indicates that low biodiversity regions should favour consumers with a broad dietary niche width, whereas high biodiversity areas will contain a greater proportion of dietary specialists. However, large studies required to assess this hypothesis on a global scale have been unfeasibly expensive. Data mining of biological archives offers an opportunity to conduct such a global study using existing data.
We conducted a data mining study to identify the diet, dietary niche width and trophic level of 4,000 marine and 1,500 freshwater fishes. The geographic distribution of these species was obtained by further data mining of the Global Biodiversity Information Facility. We subsequently used a generalised additive modeling approach to examine the effect of location, biodiversity, temperature and other associated variables on mean and median dietary niche width and trophic level of the fish community in different regions of the planet.

Results/Conclusions

In marine fishes, biodiversity, latitude and sea surface temperature all had a significant influence on the mean and median niche with of fish communities. Mean and median niche width of marine fishes was lowest equatorial biodiversity hotspots with comparatively high water temperature and biodiversity, and highest polar regions with low water temperature and biodiversity. An interesting variation was observed between Antarctic and Arctic communities with highest mean and median niche width values evident in the southern seas. In contrast, mean and median trophic level was highest in the open ocean and was not influenced by biodiversity or surface temperature.

Dietary niche width in freshwater fishes also displayed a negative relationship with biodiversity. Mean and median niche width of freshwater fishes was highest in Arctic and subarctic regions and lowest in equatorial regions. GAM models indicated that biodiversity was the predominant factor driving this variation in consumer niche width.

The trophic ecology of fishes varies across the globe.  In both marine and freshwater fishes this variation relates to a prevalence of dietary specialists in highly biodiverse regions. These data support the current paradigm, revealing that increased consumer density and diversity is facilitated by species specialising on distinct resources.