Tag Archives: fragmentation

roads and railways as wildlife movement corridors?

At least, I think that is what this paper in Conservation Biology is about. The key conclusion is that biodiversity impacts (of the roads and rails themselves? it’s unclear) can be reduced by up to 75%. I am presuming this is by locating a linear park of sufficient width along the road or railway. Presumably you might need to do something to keep the animals off the road too. Could a few larger reserves located along the corridor reduce the impact to zero? I would find it very encouraging both to know that it is possible and to know that we have the quantitative tools to accurately predict the outcomes of policy and design choices.

Quantifying the conservation gains from shared access to linear infrastructure

The proliferation of linear infrastructure such as roads and rail is a major global driver of cumulative biodiversity loss. Creative interventions to minimise the impacts of this infrastructure whilst still allowing development to meet human population growth and resource consumption demands are urgently required. One strategy for reducing habitat loss associated with development is to encourage linear infrastructure providers and users to share infrastructure networks. Here we quantify the reductions in biodiversity impact and capital cost under linear infrastructure sharing and demonstrate this approach with a case study in South Australia. By evaluating proposed mine-port links we show that shared development of linear infrastructure could reduce overall biodiversity impacts by up to 75%. We found that such reductions are likely to be limited if the dominant mining companies restrict access to infrastructure, a situation likely to occur without policy to promote sharing of infrastructure. Our research helps illuminate the circumstances under which infrastructure sharing can minimise the biodiversity impacts of development.

cheetahs: going…going…gone?

In today’s depressing conservation news, cheetahs are in serious trouble.

Led by Zoological Society of London (ZSL), Panthera and Wildlife Conservation Society (WCS), the study reveals that just 7,100 cheetahs remain globally, representing the best available estimate for the species to date. Furthermore, the cheetah has been driven out of 91% of its historic range. Asiatic cheetah populations have been hit hardest, with fewer than 50 individuals remaining in one isolated pocket of Iran…

To make matters worse, as one of the world’s most wide-ranging carnivores, 77% of the cheetah’s habitat falls outside of protected areas. Unrestricted by boundaries, the species’ wide-ranging movements weaken law enforcement protection and greatly amplify its vulnerability to human pressures. Indeed, largely due to pressures on wildlife and their habitat outside of protected areas, Zimbabwe’s cheetah population has plummeted from 1,200 to a maximum of 170 animals in just 16 years – representing an astonishing loss of 85% of the country’s cheetahs.

Scientists are now calling for an urgent paradigm shift in cheetah conservation, towards landscape-level efforts that transcend national borders and are coordinated by existing regional conservation strategies for the species. A holistic conservation approach, which incentivises protection of cheetahs by local communities and trans-national governments, alongside sustainable human-wildlife coexistence is paramount to the survival of the species.

So it’s habitat loss and the relentless expansion of the human footprint, again. Are Africans just particularly callous toward the loss of the natural world? No, Africa is just one of the last places a lot of the large, charismatic animals are left. We had them elsewhere, but we have long forgotten them. Solutions exist. But I am in a pessimistic mood right now so I don’t think this time will be different, the declines and collapses will just continue to come faster and be more obvious until maybe some things will be done, but most likely they will be too little, too late. Too little, too late, but better than nothing. How is that for a silver lining?



David Quammen (author of one of my all-time favorite nonfiction books, The Song of the Dodo: Island Biogeography in an Age of Extinction) has a long article in National Geographic about Yellowstone National Park which touches on some of the same things.

The Greater Yellowstone Ecosystem is bigger than any other park complex in the lower 48 states. And size matters. A resonant study published in the journal Nature back in 1987, by a young ecologist named William Newmark, revealed that among 12 national parks and park complexes in the western United States, all except two had lost mammal species in the years since they had been established, but that Greater Yellowstone, as the largest, had lost fewer species than almost all others. Most of those local extinctions had resulted not from direct human persecution—as the wolves of Yellowstone had been persecuted to oblivion—but from the natural processes of extinction characteristic of islands: When habitat is constrained within a limited area, animal populations remain small, and small populations tend to wink out, over time, because of accidental factors such as disease, fire, hard weather, and bad luck. Greater Yellowstone had lost less of its mammal diversity by natural attrition than had small parks such as Zion, Bryce Canyon, and Mount Rainier. Its size, evidently, had served it well.

Newmark’s original work has been challenged in some particulars during the decades since, but its basic conclusion remains sound: Size matters. The size of the Yellowstone complex helped preserve big, fearsome, wide-ranging, combative animals such as the grizzly, each one of which demands a large territory. No other park in the lower 48, apart from Glacier National Park along Montana’s Canadian border, now supports robust populations of the three greatest living North American carnivores—the grizzly, the wolf, the mountain lion—as well as such other predaceous animals as the wolverine, the coyote, the bobcat, and the red fox. Yellowstone is our wildest park south of the border complex that includes Glacier, in part because it’s our biggest.

The other good thing about geographical bigness is that, besides giving space to large predators with broad territorial needs, it usually encompasses habitat diversity as well as sheer space, thereby sheltering a greater variety of creatures at all levels of size, living all modes of life.

Because I am interested in island biogeography and I like the idea of having seminal papers at my fingertips, I looked up the Newmark article mentioned above.

A land-bridge island perspective on mammalian extinctions in western North American parks
Nature 325, 430 – 432 (29 January 1987); doi:10.1038/325430a0

In recent years, a number of authors have suggested several geometric principles for the design of nature reserves based upon the hypothesis that nature reserves are analogous to land-bridge islands. Land-bridge islands are islands that were formerly connected to the mainland and were created by a rise in the level of the ocean. Land-bridge islands are considered supersaturated with species in that the ratio of island to mainland species numbers is higher than expected from the area of the island. As a result, the rate of extinction should exceed the rate of colonization on a land-bridge island, resulting in a loss of species that is suggested to be related to the size and degree of isolation of the island. If nature reserves are considered to be similar to land-bridge islands, because most are slowly becoming isolated from their surroundings by habitat disturbance outside the reserves, several predictions follow. First, the total number of extinctions should exceed the total number of colonizations within a reserve; second, the number of extinctions should be inversely related to reserve size; and third, the number of extinctions should be directly related to reserve age. I report here that the natural post-establishment loss of mammalian species in 14 western North American national parks is consistent with these predictions of the land-bridge island hypothesis and that all but the largest western North American national parks are too small to retain an intact mammalian fauna.

It’s easy to get depressed. Even if we preserved a lot of big open spaces, left them completely alone, and there were no such thing as pollution or climate change, a smaller nature would still be a less healthy nature. The only silver lining is that if we had a really thorough knowledge of how the shapes of preserved lands and the connections between determine their ecosystem health, we could theoretically come up with land use policies and practices to produce the best possible ecosystem health in the remaining space available.

There is research going on in this area:

A simplified econet model for mapping and evaluating structural connectivity with particular attention of ecotones, small habitats, and barriers
Wei Houa, Marco Neubertb, Ulrich Walzc
Landscape and Urban Planning
Volume 160, April 2017, Pages 28–37

Small habitats and ecotones are recognized as key structures in preserving biodiversity and maintaining landscape connectivity. However, most analyses of landscape pattern have not fully accounted for these elements. This leads to an underestimation of the landscape heterogeneity, especially at the local scale. This research aims to evaluate the structural connectivity for a source habitat (i.e., forest) with particular consideration of the roles of ecotones, small habitats, and barriers. A multi-buffer mapping procedure based on vector data is applied on two comparative test sites for mapping ecological networks (econets) which are composed of forest patches, ecotones, corridors, small habitats, and barriers. On this basis, several indices are proposed for quantitative evaluation of structural connectivity of econets. The application of the indices show that our approach can be useful for analyzing econet connectivity and identifying the roles of critical landscape elements, for example the barriers’ effect on overall forest connectivity. Within an econet, ecotones function as extension of forest edges which can increase the intrapatch connectivity; small habitats play the role of stepping stones which can enhance interpatch connections among forest habitats. The proposed econet model provides a generalized illustration of landscape connectivity and can be used to compare and monitor forest pattern.

connectivity and corridors

From Conservation Biology:

Connecting science, policy, and implementation for landscape-scale habitat connectivity

In an increasingly fragmented world, networks of habitat corridors are critical to support movement of organisms between habitat patches and the long-term persistence of species. The science of corridor design and the policy of corridor establishment are developing rapidly, but often independently. Here we assess the links between the science and policy of habitat corridors, to better understand how corridors can be effectively implemented, with a focus on a suite of landscape-scale connectivity plans in tropical and sub-tropical Asia. Our synthesis suggests that the process of corridor designation may be more efficient if the scientific determination of optimal corridor locations and arrangement is synchronized in time with the achievement of political buy-in and policy direction for corridor designation. Land tenure and the intactness of existing habitat in the region are also critical factors –optimal connectivity strategies may be very different if there are few, versus many, political jurisdictions (including commercial and traditional land tenures) and intact versus degraded habitat between patches. We identify financing mechanisms for corridors, and also several important gaps in our understanding of effective corridor design including how corridors, particularly those managed by local communities, can be protected from habitat degradation and unsustainable hunting. Finally, we point to a critical need for quantitative, data-driven models that can prioritize potential corridors or multi-corridor networks based on their relative contributions to long-term metacommunity persistence.

designing fragmented ecosystems

This article in Trends in Ecology and Evolution is about purposely controlling spatial fragmentation in ecosystems in order to maximize ecosystem services. If I understand correctly, their hypothesis seems to be that a system that is fragmented in a carefully designed way could provide more ecosystem services than an unfragmented system.

Landscape structure and fragmentation have important effects on ecosystem services, with a common assumption being that fragmentation reduces service provision. This is based on fragmentation’s expected effects on ecosystem service supply, but ignores how fragmentation influences the flow of services to people. Here we develop a new conceptual framework that explicitly considers the links between landscape fragmentation, the supply of services, and the flow of services to people. We argue that fragmentation’s effects on ecosystem service flow can be positive or negative, and use our framework to construct testable hypotheses about the effects of fragmentation on final ecosystem service provision. Empirical efforts to apply and test this framework are critical to improving landscape management for multiple ecosystem services.

This idea is important to the idea that we could hypothetically design a civilization that is not only less bad than the one we have now, but one that is actually good for the planet and people.