"There is a general perception that livestock grazing is bad for wildlife," Jennifer Schieltz told environmentalresearchweb. "And a number of studies, on various species of wildlife, have indeed found this result. But there are also studies showing that livestock can sometimes have positive effects on wildlife as well."

This got Schieltz and colleague Daniel Rubenstein thinking about the relative amount of positive and negative effects of livestock grazing on wildlife. So they decided to conduct an evidence-based review, "comprehensively searching the literature and pulling out all work…done on a topic, rather than picking and choosing certain examples."

The pair found a number of patterns but also several gaps in the available data. The vast majority of studies have been in North America, with Europe as the runner-up. Most research has examined birds and mammals, with only a little covering reptiles or amphibians. And even within mammals, some types have come under scrutiny more than others.

"Among ungulates – hoofed animals – most of the studies have been on deer and elk in North America, with very little research conducted on grazing ungulates like zebras or gazelles in Africa and Asia," said Schieltz. "Wildlife interactions with people vary by continent, so what happens in Africa, where livestock and wildlife have interacted for much longer than in the new world, might be very different. Knowing that these biases and gaps exist is an important first step in guiding future research."

There were already numerous reviews of livestock grazing and bird life, Schieltz and Rubenstein discovered, so they focused on analyzing the mammal studies, dividing the animals by size. Small mammals, they found, typically responded to livestock grazing according to whether they preferred open vegetation or more dense cover. Voles, harvest mice, cotton rats and shrews, which need to hide from their predators, tended to respond badly to grazing, whilst deer mice, kangaroo rats, ground squirrels and lagomorphs showed a more variable or positive reaction. Birds often show similar trends, with livestock promoting birds that favour open, disturbed habitat.

Hoofed mammals, on the other hand, were more complicated. They had more negative responses to livestock grazing than positive ones but most of the studies were of deer and elk, which are browsers, taking leaves and shoots from plants some way above the ground, such as shrubs, or mixed feeders, combining browsing with grazing.

There was some evidence from Africa that grazing species such as plains zebra can respond positively to livestock grazing, particularly in the wet season. But there’s a strong need for more research on hoofed mammals with different diets and body sizes, particularly in the developing world and on longer time scales.

"There are lots of important questions still to be answered, and those answers will have huge implications for the way livestock are managed around the world," said Schieltz. "In many places, conservation efforts are increasingly aimed at managing land for livestock–wildlife coexistence. The patterns we show about how different species are likely to respond to livestock grazing could help managers adjust or target their livestock grazing to reduce negative impacts or promote coexistence."

Schieltz herself is conducting field work on how cattle grazing impinges on wild grazing ungulates in East Africa, and Rubenstein is examining how new "planned grazing" strategies for livestock might lead to changes in the wildlife–livestock relationship.

The team reported the analysis in Environmental Research Reviews, where Rubenstein is reviews editor.

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