Trophic control of mesopredators in terrestrial ecosystems: top‐down or bottom‐up?

Abstract

It has been argued that widespread extinctions of top predators have changed terrestrial ecosystem structures through mesopredator release, where increased abundances of medium-sized predators have detrimental effects on prey communities. This top-down concept has received much attention within conservation biology, but few studies have demonstrated the phenomenon. The concept has been criticized since alternative explanations involving bottom-up impacts from bioclimatic effects on ecosystem productivity and from anthropogenic habitat change are rarely considered. We analyse the response of a mesopredator (the red fox) to declines in top predators (wolf and Eurasian lynx) and agricultural expansion over 90 years in Sweden, taking bioclimatic effects into account. We show a top-down mesopredator release effect, but ecosystem productivity determined its strength. The impacts of agricultural activity were mediated by their effects on top predator populations. Thus, both top-down and bottom-up processes need to be understood for effective preservation of biodiversity in anthropogenically transformed ecosystems.

Ecological rules governing helminth–microparasite coinfection

“…In some senses, this is unsurprising; microparasites are organisms, after all, and there is no reason to suspect that they are exempt from ecological processes that shape the abundance of organisms in macroecosystems (e.g., refs. [17][18][19][20]. Furthermore, IFN-␥ is central to the clearance of virtually all microparasites, despite differences in the details of which cell types or anatomical location might be involved (27,30).…”

“…However, the complexity of within-host interactions (12)(13)(14)(15)(16) can make it difficult to predict how one infection will affect the course of others. Disentangling such complexity is a core activity of community ecologists, who in recent years have successfully identified trophic rules that determine, for example, the abundance of organisms in marine (17) as well as tropical (18,19) and temperate (20) terrestrial ecosystems. These trophic rules include ''bottom-up'' control of population size via resource limitation and ''top-down'' control via predation (21).…”

“…These trophic rules include ''bottom-up'' control of population size via resource limitation and ''top-down'' control via predation (21). Only by considering regulation by both resources and consumers have ecologists been able to explain the abundance of organisms across such diverse communities (17)(18)(19)(20). One major finding is that the relative importance of top-down and bottom-up control mechanisms varies among species and ecosystems; a charismatic example of this is provided by African savannah systems, in which zebra populations are primarily controlled by predators, whereas wildebeest are more strongly regulated by the quality and quantity of plant matter available for them to eat (18).…”

Red foxes colonizing the tundra: genetic analysis as a tool for population management

“…As a consequence of human-mediated landscape changes and increasing temperatures in various ecosystems, the European red fox population has during the last century expanded in numbers and geographic range (Hersteinsson and Macdonald 1992;Selås and Vik 2006;Elmhagen and Rushton 2007). In southern Sweden, the red fox population underwent a demographic increase in response to the intensified land use during the nineteenth century (Elmhagen and Rushton 2007), while red foxes in northern areas expanded in range during the same time period (Hersteinsson and Macdonald 1992). Tundra red fox abundance may benefit from changes in reindeer herding strategies that mediates higher food availability (Killengreen et al 2011).…”

Cascading predator control interacts with productivity to determine the trophic level of biomass accumulation in a benthic food web

“…Accordingly, field studies support a positive relationship between primary production and trophic cascades in some systems (e.g., Sinclair et al 2000;Elmhagen and Rushton 2007;Moksnes et al 2008;Eriksson et al 2009;Sieben et al 2011), whereas a recent set of meta-analyses suggests that, in general, it is the traits of consumer species, and not productivity, that determine the prevalence of trophic cascades in predator removal experiments (Borer et al 2005(Borer et al , 2006. However, models that incorporate short-term population dynamics and allow for dispersal suggest that the an alternating positive relationship between trophic levels and primary productivity should also appear in environments where consumers immigrate and emigrate actively between patches depending on resource availability (Wootton and Power 1993;Oksanen et al 1995;Nisbet et al 1997).…”