Waxing and waning of a cotton rat (Sigmodon toltecus) monoculture in early tropical restoration

Abstract

As part of an experimental restoration of seed-dispersal processes in a fragmented agricultural landscape, we recorded rodent colonization of fenced plots in active cattle pasture over 10 years. The design included 16,900m2 fenced cattle exclosures that were either planted with seedlings of native animal-dispersed trees, planted with seedlings of native winddispersed trees, or unplanted controls to simulate natural succession. Near the end of the dry season in late May and early June from 2007 to 2016, five Sherman live traps were placed in each plot for 66 hr per plot, resulting in 1,584 trap hours per year. Eight species of rodents were captured. Of 697 individuals, 644 (92%) were cotton rats (Sigmodon toltecus); only 1 other species, Coues’ rice rat (Oryzomys couesi), accounted for >1% of the total. S. toltecus accounted for at least 96% of the biomass of >50 kg of rodents captured. This species dominated the rodent community while most plots were grass- or fern-covered from 2007 to 2010. Thereafter, the question of interest was whether S. toltecus change in population numbers could be attributed to normal fluctuations of small rodents or to habitat change. The minimum number alive declined from 149 in 2010 to 20 in 2016. Overall, and frequently within years, low S. toltecus captures reflected high woody cover from shrubs and trees. A virtual Sigmodon monoculture prevailed until dense herbaceous cover was replaced by forest understory.