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On Productivity as a Predictor of Rodent and Carnivore Diversity
Author(s) -
Owen James G.
Publication year - 1988
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1941270
Subject(s) - carnivore , ecology , productivity , trophic level , disturbance (geology) , biology , herbivore , species diversity , rodent , macroeconomics , economics , predation , paleontology
Tilman's model predicts an asymmetric relationship, with ascending, peak, and descending parts, between plant species diversity and a resource gradient. I evaluated the applicability of Tilman's model to mammals by regressing rodent and carnivore species diversity on estimates of net aboveground primary productivity. Rodent diversity was highest at low productivity levels and declined as productivity increased. Although my data did not confirm the upslope and peak phases of Tilman's model, this may be because I did not sample from areas of extremely low productivity. Published studies from very dry desert habitats indicate that rodent diversity increases rapidly across a narrow gradient of very low productivity and peaks at moderately low levels. This suggests that rodents, which are largely herbivorous, exhibit an asymmetric productivity—diversity curve similar to that predicted by Tilman for plants. The rodent data are also consistent with the intermediate disturbance hypothesis, which predicts diversity as a peaked function of a disturbance gradient. Rainfall predictability, which may function as a disturbance, is inversely related to my plant productivity gradient. The regression curve for carnivores helps to distinguish between these two hypotheses. At a given locality carnivores and rodents should be exposed to about the same disturbance levels and according to the intermediate disturbance model should peak at about the same place. Since carnivores as a whole are about one trophic level above rodents, if plant productivity controls diversity the peak for carnivores should occur at about an order of magnitude of productivity higher than the peak for rodents. My carnivore diversity data exhibit upslope, peak, and downslope phases and are shifted to higher levels of productivity by about one order of magnitude. This provides evidence against the intermediate disturbance hypotheses and corroborates predictions of Tilman's model as applied to mammals.