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Protected areas best conserve mammalian diversity when connected with corridors, biologged weasels show

  • For protected area (PA) networks to be an effective conservation tool, they should be well-connected to allow species movement through unprotected landscapes, but questions remain on what configuration of natural features can best facilitate animal movement.
  • A recent study compared three theories of animal movement (structurally intact corridors, least-cost paths, and stepping stones) by analyzing the fine-scale movements of GPS-tagged fishers, a member of the weasel family. They found the tagged fishers consistently moved along structurally intact, natural corridors across a PA network.
  • With the Aichi 2020 Biodiversity Targets in mind, the authors highlight that simply increasing the number of protected areas alone may not achieve the objectives of the protected area network amidst an increasingly fragmented landscape; the conservation of natural corridors between PAs may be equally important, something for future planners to consider.

In a recently published  study, Canadian researchers monitored the fine-scale movements of GPS-tagged fishers (Pekania pennanti), a member of the weasel family, across a terrain of over 700 protected areas (PAs) in Alberta, Canada. They found that corridors of natural structurally intact habitat may be just as critical as the protected areas themselves for conserving forest-dwelling mammals.

Connectivity over quantity

In the face of climate change and loss of natural vegetation, increasing public awareness over the accelerated rate of global species extinction has compelled governments in more than 240 countries to dramatically increase the number of protected areas over the last 20 years. According to a report by the United Nations Environment Programme (UNEP), there are over 200,000 terrestrial protected areas around the world being governed on a national level as of 2016. But a majority of those PAs exist in increasingly patchy, fragmented networks within an ever-expanding human-dominated landscape.

This is bad news for the animals these reserves are meant to protect.

Examples of two wildlife movement theories: (above) The stepping stone theory predicts that patches of disconnected habitats best facilitate the movement of species within a network of protected areas. Image by José Luiz Viana do Couto, Rede Agronomia(below) The corridor theory suggests that habitat “bridges” that are structurally intact best facilitate species movement between protected areas. Image by Laury Cullen Jr,  CC BY-SA 4.0.

Research has shown that individual animals across more than 50 species move shorter distances in fragmented habitats; such changes in movement behavior may negatively affect an animal’s survival and reproduction.

Some animals have large home ranges and others migrate seasonally, so a small, isolated PA might be unable to support enough individuals to form a sustainable population on its own.

So, is simply creating more protected areas the solution to halting the extinction crisis? Certainly not, according to Frances Stewart, a wildlife ecologist at the University of Victoria who led the study. “The quality of protected areas and the landscape between them is an important feature, not just the quantity of protected areas,” she told Mongabay. “As we develop more protected areas, we must consider how animals will piece them together.”

“The importance of connectivity between protected areas is acknowledged globally, and considered in protected area planning,” Stewart said. The question remains, how do animals actually move across fragmented landscapes and what vegetative configuration can best facilitate their movements in between PAs?

Stewart and her colleagues set out to answer this question by testing three common theories of functional connectivity, defined as “the degree to which the landscape facilitates or impedes movement among resource patches,” by tracking the movements of fishers across a network of several hundred PAs.

The first is the corridor theory, which can be visualized as a habitat “bridge”. In this scenario, animals move across long thin strips of forested land (or whatever the native vegetation is) that remain between two designated protected areas. The second is the least-cost paths theory, which predicts that animals will move across the PA network and surrounding unprotected matrix based on the physical “cost,” in terms of resource density, of making those movements. The third is the stepping-stone theory, which suggests that animals will migrate or disperse among larger protected areas by stopping in smaller, disconnected forest patches in between them.

 

Characteristics describing the three common theories of landscape connectivity across a protected area network analyzed in this study. The black dotted pathways in each map show hypothetical movements of fishers within each model. Image is adapted from Figure 3 from Stewart et al (2019),  CC  2.0.

Follow the fisher to find out

The fisher is a small carnivorous mammal in the mustelid (weasel) family native to North America.

“We chose to study fishers for this research because they are a species in the middle of the mammal food chain – they are eaten by larger species, but also eat many smaller species,” Stewart said. “This means that their movements and use of their surroundings is generally indicative of other mammals within the ecosystem and allows us to generally say what mammals need.”

The fisher (Pekania pennanti) is a forest-dwelling member of the weasel family with thick brown fur, generally the size of a domestic cat. In the 1800s, fishers nearly went extinct due to logging and over-trapping. Their numbers have steadily increased since then, but the exact status of their population is still unknown. Image by Christopher Lee, courtesy of Frances Stewart.

The research team carried out the study in the Beaver Hills Biosphere in east-central Alberta, Canada. The area spans 1,596 square kilometers (616 square miles) and is an excellent example of a protected area matrix; 763 protected areas of varying sizes occur within the biosphere alongside areas of human development and unprotected but still naturally vegetated areas.

To better understand how animals piece together their landscape, the research team captured 10 fishers, representing about 17 percent of the estimated population of 58 adult individuals, and fitted them with Global Positioning System (GPS) tracking collars. Once they released the animals back into the wild, the GPS units collected their point locations over an average of 33 days, at continuous five-minute intervals if the animal was moving faster than 10 centimeters (3.9 inches) per second.

To test their three hypotheses, the researchers measured the fine-scale movements of the tagged fishers. These included the speed and tortuosity of the discrete five-minute steps. The team measured speed as the linear distances between successive GPS points (the number of meters moved every 5 minutes) and tortuosity as the turn angles between successive GPS points. They used these two variables to infer “residency” time at any one spot. For example, movements with many turns and short step lengths indicate longer time spent within an area. Conversely, long linear steps indicate forward movement and shorter residency time.

The research team fitted 10 fishers with GPS tracking collars to better understand how these animals move around varied landscapes. Image courtesy of Frances Stewart.

Using a digital map of Beaver Hills Biosphere and the mapping tool ArcGIS, the team quantified fisher movement across 15 landscape features, broadly categorized as anthropogenic, natural habitat, or protected area.

The researchers predicted that if the stepping-stone theory best explained fishers’ use of space, the animals’ movements should indicate longer residence time (i.e. short, non-linear distances between GPS points) within protected areas. If the corridor theory was correct, fishers should move along natural forested areas. And if the least-cost paths theory best described fisher movement patterns, the fisher movements should comprise shorter steps, indicating longer residence time, in areas with high movement cost, and long, linear movements (a sign of traveling) across landscapes with low movement costs.

The research team’s analysis of the tracking data across Beaver Hills Biosphere showed that “fishers predominantly used natural features as corridors, rather than crossing multiple landscape features with different movement costs or using stepping stones within or between protected habitat patches.”

In other words, the study indicated that the corridor theory best explained fisher movement across this PA network. “The presence of multiple protected areas alone may not facilitate landscape connectivity unless structurally connected by natural, polygonal, landscape features,” the authors point out.

Fishers are small, solitary, elusive, and primarily carnivorous. They are known to hunt and eat rabbits, snowshoe hares, squirrels, raccoons, mice, reptiles, amphibians, house cats, and are one of the few specialized feeders of porcupine. They will also eat berries and fruit when prey is not available. They are native to North America, and their range cover much of the boreal forest in Canada and the northern United States. Image by Michel Rathwell, Flickr, CC BY 2.0.

Future implications

“What we show here is that corridors – as a specific type of connectivity –are very important for the fisher, and probably also other mammal species,” Stewart said.

She added that she hoped that the study’s findings can better inform protected area planning in the future.

“Corridors themselves are rarely explicitly incorporated into landscape, and importantly, protected area planning partly because controlling what happens on the land between protected areas is difficult for planners,” Stewart said. “We hope this work helps planners and landowners understand the importance of how the actions taken on their land affects the bigger picture of protecting landscapes for biodiversity conservation generally.”

In 2010, the United Nations’ Convention on Biological Diversity brought together 194 nations to Nagoya, Japan, where representatives set 20 Biodiversity Targets with the goal of meeting them by 2020. Specifically, Target 11 calls for the protection of at least 17 percent of land and 10 percent of marine areas. The results of this study suggest that “focusing on maintaining or restoring natural landscape features within the matrix of existing PA networks,” or establishing PA networks within regions that already contain an abundance of natural habitats, “will greatly aid conservation objectives.”

“We show that increasing the extent of the global protected area network is not a stand-alone solution to connecting protected areas,” the researchers say in their paper. “The conservation of natural landscape features between protected areas is the mortar that binds them together.”

Citation

Stewart, F. E., Darlington, S., Volpe, J. P., McAdie, M., & Fisher, J. T. (2019). Corridors best facilitate functional connectivity across a protected area network. Scientific reports, 9(1), 10852.

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