In issue 56:8 we showcase the research, technology and mitigation efforts going into the management of wide-ranging species today. Join Associate Editor, Johan du Toit in exploring this selection of work, free to read in the journal for a limited time.
The ability to range widely across our planet conveys a game-changing advantage to certain animals, as was realised by humans when they discovered that horses can be ridden across expansive plains and boats can be sailed across deep water. There is no longer any location on the surface of a continent or an ocean that humans cannot reach, and will not reach if it is worth their while. On land, a web of linear infrastructure is expanding and intensifying to facilitate the increasing movement of people, their goods, and their waste. On water, ships of all nationalities can be found anywhere, especially in shipping lanes between ports and in areas where industrial fishing is profitable. In between, there is junk of all types, and especially plastic, that is ‘disposed’ of in the easiest way a person can turn their unwanted responsibility into another individual’s problem – with that other individual usually being of another species. Yet humans are only one of a great many species that benefit from – and indeed depend upon – mobility on a planetary scale, for which the activities of humans are now compromising the evolutionary advantages of efficient locomotion. The papers in this Journal of Applied Ecology Spotlight draw attention to the need for improved management of wide-ranging species, or at the very least enhanced awareness of the extent to which we are getting in their way.
Sometimes the best way to help is to get out of the way
Long-winged birds and long-legged mammals are adapted for utilising resources that are widely dispersed in space and time, with albatrosses and ungulates being prime examples within their respective classes. For an albatross, living a successful life of 60 or more years involves foraging on a planetary scale, mating for life, incubating one egg every second year and raising the chick on an island without ground predators. That life-history strategy was successful until boats brought rodents and cats to their nesting islands, and trawl nets, longline tackle, and plastic waste to their feeding grounds. Simple mitigation measures can substantially reduce the killing of seabirds (euphemistically called ‘bycatch’) on longlines, yet, as the analysis of Clay et al. shows, threatened seabird populations continue to decline. That suggests inadequate attention to bycatch mitigation even by compliant fishing vessels, let alone all the illegal, unreported, and unregulated fishing vessels on the high seas.
On land, nomadic and migratory ungulates have to move widely between feeding areas to build enough reserves in the green season to cover the costs of reproduction and survival through the brown and white seasons. Using GPS telemetry, Nandintsetseg et al. found that during just a few years, an individual Mongolian gazelle could roam over 100,000 km2 of the world’s least populated steppe, but now roads, rail lines, fences, towns and oil and gas fields lie in their way. There is no single protected area in the Mongolian eastern steppe big enough to include the annual nomadic range of any single gazelle. They thus have to contend with linear structures such as fences, which impede the movement of 80% of gazelles. When they encounter a fence, they will typically walk along it for more than 10 km, searching for a place to cross.
As shown by Sawyer et al. in the western USA, even ungulates that are able to get over fences and other linear structures are surprisingly sensitive to variations in the condition of their migratory routes between seasonal ranges. Mule deer that use routes exterior to the more direct interior routes of their winter herd members suffer a 30% decline in survival probability. It remains unclear why that is, but what is obvious explanation is that the annual cycle of a migrating mule deer operates within a tight physiological tolerance range. Consequently, when humans disturb habitat and obstruct travel anywhere along an average 73 km migratory route, some impact on mule deer survival is to be expected.
Predators learn, adapt, take opportunities and interact, so managers should too!
For most wildlife species, and especially large vertebrates, surviving in the Anthropocene means adapting to the sprawl of human infrastructure. Many Northern Hemisphere cities include red foxes as remarkably well adapted urbanites, and the camera trapping work of Parsons et al. in two eastern USA cities shows how good they are at sharing space. Urbanisation reduces and fragments forest habitat so that remaining options are limited for all species. Now, red and grey foxes find themselves sharing tight green spaces with bobcats and coyotes, forcing them to interact and coexist to an extent that would never occur outside the suburbs.
Large predators are opportunistic, and as long as they can dodge bullets and learn to avoid poison and traps, they will find ways to exploit the livestock and garbage dumps of humans. They can however, take more opportunities than are good for them, and that applies especially to wide-ranging species. Gervasi et al. describe an especially illustrative case in Scandinavia, where the national border between Norway and Sweden means nothing to a wolverine, but a great deal to the wildlife management agencies on either side. Most rural Norwegians have vehemently negative attitudes towards large predators. They are especially intolerant of any depredation of their apparently precious yet semi-feral sheep, even with government compensation. Nevertheless, try as they might, sport hunters and the wildlife agency cannot bring the wolverine population of southern Norway down to their management objective. That is largely because Swedes are less militant against predators, allow higher densities, and thereby provide a source for a steady flow of wide-ranging wolverines to replace some of those shot on the other side of the border. In a random sample of six or seven wolverines shot in Norway, one will be an immigrant from Sweden, drawn to the ‘attractive sink’ of low competition and high opportunity created as an unintended consequence of a management mismatch across the line.
If a tree falls in a forest, or a gazelle walks into a fence …
The papers in this Spotlight collectively shine a revealing light on some stark realities. The technology (satellite-based remote sensing, telemetry, biologging, camera trapping, etc.) for monitoring the movement, behaviour and welfare of wide-ranging animals is well developed, provides accurate data, and is commonly used worldwide. Studies using that technology consistently find wide-ranging species to be impeded by anthropogenic factors. Mitigation – such as adapting longline tackle, erecting crossings over fences and roads in key places, removing unnecessary fences, or simply getting managers and stakeholders in neighbouring countries to talk to one another – should be feasible, affordable, and effective. Achieving adequate implementation remains problematic though, and a major reason is that wide-ranging animals suffer their anthropogenic tragedies in remote places, out of sight of the people who might make a fuss if only they knew they should. This Spotlight might help. For wide-ranging species to persist they must be allowed to range freely and, for many species, applied ecologists know where humans are obstructing them and how their populations are being affected. The global community should know too.
Read the full Spotlight, Management of wide-ranging species, in issue 56:8 of Journal of Applied Ecology. The papers are free to read for a limited time.