Seed Size Diversity, Bird Species Diversity and Interspecific Competition

Publication Type:Journal Article
Year of Publication:1983
Authors:Thompson, PM, Lawton, JH
Journal:Ornis Scandinavica
Date Published:1983
ISBN Number:00305693
Keywords:Carduelis, Carduelis chloris, Chloris, Chloris chloris, Fringilla, Fringilla montifringilla, Fringillidae, Merula, Montifringilla, Passer, Passer montanus, Passeridae, Salicipasser montanus, Turdidae, Turdus, Turdus maximus, Turdus merula
Abstract:We created experimental patches with one, two or three sizes of seeds, and recorded the number of species, and numbers of individuals of each species of birds exploiting the seeds in winter. Bird species diversity increased with seed size diversity. The frequency of visits made by each species of bird to the single-seed plots provided us with a measure of seed-size preference for each species. For example, most Bramblings Fringilla montifringilla were recorded on plots with sunflower seeds (the largest seeds); Tree Sparrows Passer montanus preferred millet, the smallest seeds, and Blackbirds Turdus merula preferred seeds of intermediate size (wheat). Using each species' seed-size preferences we were then able to compute the overlap in seed-size use between species. Dietary overlap was not significantly related to similarity in body-size. Competition between species was assessed by fitting Lotka-Volterra competition equations to species counts on the two- and three-seed plots. Most species-pairs showed no evidence of significant interactions. Of those pairs that did interact significantly, several showed significant mutualistic, not competitive interactions. Both competitive and mutualistic interactions varied with seed diversity. Only two species pairs showed consistent competitive interactions on plots with two seed sizes and on plots with three seed sizes; they were, Blackbird-Greenfinch Carduelis chloris, and Blackbird-Tree Sparrow. We compared our estimates of species' competitive and mutualistic effects on each other with our estimate of dietary overlap. There was no significant relationship between dietary overlap and realised interaction. Our results are briefly discussed in relation to current views on the role of interspecific competition as a force structuring bird communities.
Short Title:Ornis Scandinavica
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith