Use of Habitat, Size of Prey, and Food-Niche Relationships of Two Sympatric Otters in Southernmost Chile

Food-niche relationships of diurnal raptors have been claimed to be shaped by either competitive interactions or opportunistic feeding. We confront these alternatives by analyzing the patterns of prey use of five assemblages of falconiforms. Our results show that food-niche breadth is not a species property but is determined by the food resources locally available; neither does it become narrower in larger assemblages nor is it correlated with raptor size. Food-niche overlaps are frequently very high and do not become smaller in larger assemblages. Mean weight of prey taken is positively correlated with raptor weight within assemblages, but varies widely across assemblages, with a single species showing manyfold differences. Weight ratios between raptors contiguous in the size axis fall well below the 2.2–3.4 expected figures, nor are they negatively correlated with the amount of food-niche overlap. Normalized distance ratios (d/w) of spacing between raptors along the food-size axis are usually smaller than the expected 1. The five assemblages are organized in feeding guilds whose size is larger where fewer prey categories are available per raptor species. In most cases we found little support for predictions based on competition-structured assemblages. This is probably because of the opportunistic feeding behavior of raptors, and perhaps also because food might not be a limiting resource for them.

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Investigation of food habit and niche relationships in a cyprinid community

Canadian Journal of Zoology ◽

10.1139/z90-267 ◽

1990 ◽

Vol 68 (9) ◽

pp. 1873-1879 ◽

Cited By ~ 18

Author(s):

Matthew K. Litvak ◽

Roger I. C. Hansell

Keyword(s):

Water Column ◽

Pimephales Promelas ◽

Food Habit ◽

Principal Coordinate Analysis ◽

Gut Contents ◽

Niche Space ◽

Benthic Food ◽

Frequency Occurrence ◽

Food Niche ◽

Niche Relationships

Study of the gut contents of a cyprinid community by means of frequency occurrence and back-predicted biomass data indicated that Pimephales promelas has a benthic food habit, consuming a high proportion of detritus and associated invertebrates. Phoxinus eos and Phoxinus neogaeus both consumed prey from the benthos and throughout the water column. A large portion of their diet also consisted of detritus, but less than that of Pimephales promelas. The community food niche was analyzed in multidimensional niche space, using principal coordinate analysis, and an algorithm for a community perspective on the multidimensional niche was used. Pimephales promelas had the smallest niche, with a high proportion of its niche hypervolume in intersection with the two Phoxinus species. Phoxinus eos had the second largest niche and was the "middle competitor" in this community. Phoxinus neogaeus had the largest niche and was overlapped the least in the community. Comparison with previous studies of food habit suggests that competition was occurring at the time of the study.

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