New research confirms wolves trigger a trophic cascade (Wisconsin)
June 14, 2013
by Callan, et al. (June 6, 2013).
This study takes advantage of the 30+ years of data on wolf pack distribution in northern Wisconsin – data collected by state wildlife biologists working to document recovery of the population under the US Endangered Species Act.
The upper Great Lakes region of the US – the northern portions of the states of Michigan, Wisconsin, and Minnesota – has seen a strong recovery of gray wolf (Canis lupus) populations over the past 30 years. The study took advantage of the 30+ years of data on varied recovering gray wolf pack distribution in northern Wisconsin – data collected by state wildlife biologists working to document recovery of the population under the US Endangered Species Act.
Put simply, trophic cascades are powerful interactions that strongly regulate biodiversity and ecosystem maintenance. It is triggered by the addition (or removal) of top predators and involving reciprocal changes in the populations of predator and prey through a food chain, which often results in dramatic changes in the balance of ecosystems. In a three-level food chain, an increase in carnivores causes a decrease in herbivores (i.e.: deer, elk, etc.) and an increase in primary producers (i.e.: plants). For example, in eastern North America the removal of wolves (Canis lupus) has been associated with an increase in white-tailed deer and a decline in plants eaten by the deer.
The results of this research indicated clear evidence that the presence of wolves is associated with a trophic cascade of events. The work of Callan et. al. provides evidence that the absence of the top predators can have pervasive impacts on the native plant communities in Wisconsin.
In general, places occupied by many wolves had a diverse understory community (forest floor) with varied kinds/sizes of vegetation. In contrast, places with few wolves were characterized by a very limited herbaceous layer (plants that are fleshy and wither after the growing season) and almost no woody-browse (i.e. trees). Although some low-populated wolf sites were characterized by an understory dominated by ferns, it was still lacking in forbs (broad-leaved plants), shrubs and tree seedlings. The percentage broad-leafed cover was higher in high-populated wolf areas
Ecologists should be concerned that this trophic cascade of events is now broken. With delisting at the federal and state levels, a heavy first wolf harvest in Wisconsin occurred this past year (2012-13), and an even heavier is one planned for this coming year (2013-2014). This marks a sad, and political, end to this valuable dynamic by legislative interference, not by science.
The authors of this study assert that the results indicate that wolf recovery in other regions of North America (such as the northeastern United States) could be vital to maintaining the ecological integrity of northern white cedar wetlands (and potentially other temperate and boreal forest systems as well). They concluded, “Whether efforts should be focused on reintroducing wolves or on increasing the connectivity between existing wolf populations and unoccupied wolf habitat should be carefully considered.”