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 16,900 m 2 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.

Preserving identity in capture–mark–recapture studies: increasing the accuracy of minimum number alive (MNA) estimates by incorporating inter-census trapping efficiency variation

“…All forms of enumeration exhibited negative bias as abundance estimators (that is, in their ability to reproduce the underlying baseline population size), particularly at low It has long been established that MNA's performance as an abundance estimator is sensitive to trapping efficiency (Hilborn et al 1976). Nevertheless, its intuitive computation and usefulness as an abundance indicator have ensured its continued use for ecological studies (Smith and Nichols 2003;Holloway et al 2012;Fritts et al 2017;Howe and Davlantes 2017), conservation assessments (Sei and Porter 2003;Meijer et al 2008), and governmental species management interventions (Ramey et al 2008;Lazenby et al 2014;Johnson et al 2016). It is particularly useful for small or endangered populations Fig.…”

“…2a). This risks low comparability if either interpopulation habitat differences (Smith and Nichols 2003) or habitat changes (Howe and Davlantes 2017) result in substantially different capture efficiencies. Similarly, if detectability and/or baseline prevalence is particularly low, as occurs for example in cetacean and other marine animal surveys (Poncelet et al 2010;Rinaldi et al 2021), eMNA's negative bias is likely to be even greater.…”

“…Therefore, while probabilistic approaches (ranging from simple Lincoln-Petersen estimators to multi-state CMR models, Pollock 2000;Lindberg 2012;Laake et al 2013) may provide more accurate abundance estimators (accurate prediction of abundance), MNA can out-perform certain probabilistic metrics as an abundance indicator (precise correlation to changes in abundance, Davis et al 2003), particularly when these approaches are hindered by obstructing terrain (as in transect distance sampling or double-observer abundance estimators) and/or cryptic animal behaviour (Corlatti et al 2015(Corlatti et al , 2017, or under conditions that violate the assumption of equal catchability (Tuyttens 2000). Such an indicator can provide crucial information for ecological inquiry, such as abundance trends in different successional stages (Howe and Davlantes 2017) or in threatened populations (Pryde et al 2005), comparative measures of abundance within a population over time (Bright Ross et al 2020), or inter-specific (Fritts et al 2017) and inter-population (Smith and Nichols 2003;Holloway et al 2012) comparisons of abundance drivers. In the case of MNA, the indicator is also directly linked to individual life-history records, making it easy to test associations between population-and individual-scale processes (Bright Ross et al 2020.…”

Demographic costs and benefits of natural regeneration during tropical forest restoration

“…Consequently, while the understory of planted plots is generally dominated by woody species, naturally regenerating plots have retained patches of invasive fern ( Nephrolepis hirsutula ) and pasture grasses ( Brachiaria and Cynodon spp.) throughout the study period (Howe & Davlantes ).…”

Return of forest structure and diversity in tropical restoration plantings

“…F I G U R E 6 Proportional abundance of the 10 most common plant families in each habitat by diameter rank on a log scale. Diameter is used as a proxy for height, given the positive allometric relationship between the variables, to visualize vertical structure by habitat (O'Brien et al, 1995) Seedling predation by large mammals is prevented with barb wire fences; herbivory by small rodents is still possible, but the impact that rodents in the plots have on seedling survival and the mechanisms driving their foraging preferences remain to be fully evaluated (but see Beltr an, 2021; Guzman et al, 2021;Howe & Davlantes, 2017). Canopy cover does differ between planting treatments, with the wind-plantings having more exposed and variable canopy covers (x ¯= 82.4%, SE = 1.39%) than animal-plantings (x ¯= 88.89%, SE = 0.5%, p = 0.048) (supplemental material 1 in .…”