Population growth of Mexican free-tailed bats (Tadarida brasiliensis mexicana) predates human agricultural activity
- Equal contributors
1 Department of Biology, Grand Valley State University, Allendale, MI 49401, USA
2 Institute of Molecular BioSciences, Massey University, Palmerston North 4442, New Zealand
3 Allan Wilson Centre for Molecular Ecology and Evolution, Palmerston North, New Zealand
4 Bio-Protection Research Centre, Canterbury, New Zealand
5 Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, USA
BMC Evolutionary Biology 2011, 11:88 doi:10.1186/1471-2148-11-88Published: 1 April 2011
Human activities, such as agriculture, hunting, and habitat modification, exert a significant effect on native species. Although many species have suffered population declines, increased population fragmentation, or even extinction in connection with these human impacts, others seem to have benefitted from human modification of their habitat. Here we examine whether population growth in an insectivorous bat (Tadarida brasiliensis mexicana) can be attributed to the widespread expansion of agriculture in North America following European settlement. Colonies of T. b. mexicana are extremely large (~106 individuals) and, in the modern era, major agricultural insect pests form an important component of their food resource. It is thus hypothesized that the growth of these insectivorous bat populations was coupled to the expansion of agricultural land use in North America over the last few centuries.
We sequenced one haploid and one autosomal locus to determine the rate and time of onset of population growth in T. b. mexicana. Using an approximate Maximum Likelihood method, we have determined that T. b. mexicana populations began to grow ~220 kya from a relatively small ancestral effective population size before reaching the large effective population size observed today.
Our analyses reject the hypothesis that T. b. mexicana populations grew in connection with the expansion of human agriculture in North America, and instead suggest that this growth commenced long before the arrival of humans. As T. brasiliensis is a subtropical species, we hypothesize that the observed signals of population growth may instead reflect range expansions of ancestral bat populations from southern glacial refugia during the tail end of the Pleistocene.