The influence of spatio-temporal resource fluctuations on insular rat population dynamics

Abstract

Local spatio-temporal resource variations can strongly influence the population dynamics of small mammals. This is particularly true on islands which are bottom-up driven systems, lacking higher order predators and with high variability in resource subsidies. The influence of resource fluctuations on animal survival may be mediated by individual movement among habitat patches, but simultaneously analysing survival, resource availability and habitat selection requires sophisticated analytical methods. We use a Bayesian multi-state capture-recapture model to estimate survival and movement probabilities of non-native black rats (Rattus rattus) across three habitats seasonally varying in resource availability. We find that survival varies most strongly with temporal rainfall patterns, overwhelming minor spatial variation among habitats. Surprisingly for a generalist forager, movement between habitats was rare, suggesting individuals do not opportunistically respond to spatial resource subsidy variations. Climate is probably the main driver of rodent population dynamics on islands, and even substantial habitat and seasonal spatial subsidies are overwhelmed in magnitude by predictable annual patterns in resource pulses. Marked variation in survival and capture has important implications for the timing of rat control.

Home ranges of introduced rats on Christmas Island: A pilot study

“…Recent studies (e.g. Russell & Ruffino ) have highlighted significant boosts in rodent population dynamics, including individual survival, following intense rainfall events and subsequent increases in primary productivity. In the context of Christmas Island, July is generally regarded as the driest time of the year, suggesting that the primary productivity of the coastal forests on Christmas Island is likely to be significantly higher than that of Hawaii's mesic forests, thereby allowing individual rats to thrive within a much smaller home range even when food supplies and fresh water are likely to be at their lowest compared with any other time of year.…”

Combined effects of climate, predation, and density dependence on Greater and Lesser Scaup population dynamics

“…In addition to direct effects on populations, e.g., through thermoregulatory effects on demography, climate can indirectly affect populations via changes to food web dynamics (Russell and Ruffino 2012) through predator-prey interactions (Wilmers et al 2007) or resource availability (McCaffery et al 2012). Moreover, changes in climate can intensify mechanisms related to density dependence (e.g., intraspecific competition, disease transmission, prey switching; Lima and Berryman 2006).…”

Spatio‐temporal variation in European starling reproductive success at multiple small spatial scales

“…), or distinct habitat types (e.g., Ozgul et al. ; Russell and Ruffino ). However, such analyses do not quantify demographic variation within these coarse subunits.…”

“…Many empirical studies aiming to quantify spatial variation in demography focus on populations that comprise distinct geographical or biological subunits, and hence where a priori spatial subdivisions appear obvious to observers (Saracco et al 2010). For example, many studies consider archipelagos (e.g., Saether et al 1999;Sonsthagen et al 2012), territorial species (e.g., Nystrand et al 2010), or distinct habitat types (e.g., Ozgul et al 2006;Russell and Ruffino 2011). However, such analyses do not quantify demographic variation within these coarse subunits.…”