Episodic outbreaks of small mammals influence predator community dynamics in an east African savanna ecosystem

Abstract

Little is known about the dynamics of small mammals in tropical savanna: a critical gap in our understanding of Africa's best known ecosystems. Historical evidence suggested small mammals peak in abundance (outbreak) in Serengeti National Park (SNP), as in agricultural systems. We asked 1) what are bottom–up drivers of small mammals and 2) do predators have top–down effects? We documented dynamics of small mammals, birds of prey, and mammalian carnivores in SNP and agricultural areas. We used climatic fluctuations and differences between unmodified and agricultural systems as perturbations to examine trophic processes, key to understanding responses to climate change and increasing human pressures. Data were derived from intermittent measures of abundance collected 1968–1999, combined with systematic sampling 2000–2010 to construct a 42‐year time series. Data on abundance of black‐shouldered kites (1968–2010), eight other species of rodent‐eating birds (1997–2010), and 10 carnivore species (1993–2010) were also collated. Outbreaks occurred every 3–5 years in SNP, with low or zero abundance between peaks. There was a positive relationship between rainfall in the wet season and 1) small mammal abundance and 2) the probability of an outbreak, both of which increased with negative Southern Oscillation Index values. Rodent‐eating birds and carnivores peaked 6–12 months after small mammals. In agricultural areas, abundance remained higher than in natural habitats. Abundances of birds of prey and mammalian carnivores were extremely low in these areas and not related to small mammal abundance. Small mammals are an important food resource for higher trophic levels in the Serengeti ecosystem. Changes in climate and land use may alter their future dynamics, with cascading consequences for higher trophic levels, including threatened carnivores. Although outbreaks cause substantial damage to crops in agricultural areas, small mammals also play a vital role in maintaining some of the diversity and complexity found in African savanna ecosystems.

Density feedbacks mediate effects of environmental change on population dynamics of a semidesert rodent

“…In (semi)arid environments, small mammals often have important roles as keystone (prey) species and ecological engineers (Kelt, ). If climate change reduced overall abundance of striped mice (and potentially other rodent species)—as predicted in this study—this could have cascading effects on the abundance of bird, reptile and carnivore predators (Byrom et al., ), on the spread of invasive species (Madrigal, Kelt, Meserve, Gutierrez, & Squeo, ), and on the plant species richness that makes the Succulent Karoo a unique biodiversity hotspot (Hillebrand et al., ). Such effects on other trophic levels could, in turn, feed back again on rodent (meta)population dynamics.…”

Rabbit biocontrol and landscape‐scale recovery of threatened desert mammals

“…The ecological driver relationships here are likely subject to dynamic complexity given the dramatic booms and busts in populations of primary consumers, which respond to patchy and unpredictable rainfall in these arid systems (Byrom et al. ; Greenville et al. ).…”

“…Other contributors to Dasycercus recovery may include increased populations of small-mammal and arthropod prey, resulting from greater primary productivity. The ecological driver relationships here are likely subject to dynamic complexity given the dramatic booms and busts in populations of primary consumers, which respond to patchy and unpredictable rainfall in these arid systems (Byrom et al 2014;Greenville et al 2014).…”

Native forest replacement by exotic plantations triggers changes in prey selection of mesocarnivores

“…Carnivores can respond positively, or negatively, to plantations depending on their ecological requirements and management prescriptions within these anthropic habitats (Acosta-Jamett and Simonetti, 2004;Di Bitetti et al, 2006;Pita et al, 2009;Mazzolli, 2010;Lantschner et al, 2012;Simonetti et al, 2013;Coelho et al, 2014). The decline in carnivore populations arising from the replacement, or loss, of natural habitats may result in cascading effects affecting the biodiversity at lower trophic levels (Jaksic et al, 1992, Thompson and Gese, 2007, Byrom et al, 2014Ripple et al, 2014). Assessing how exotic plantations alter prey populations and how carnivores respond to these habitatmediated changes in prey abundance could provide a bridge between sustainable forestry management and the trophic ecology of carnivores.…”