Invasive species and conservation in the Cape Horn Biosphere Reserve

This project focuses on studying the dynamics and impact of invasive mammalian species in Cape Horn Biosphere Reserve in Southern Chile. I started working in the area as part of my Ph.D. study and now I continue collaborating with colleagues and friends from the Subantarctic Biocultural Conservation Program.

 

Invasive species are a major global problem. In the past 70 years twelve mammal species were introduced in the Magellanic region.

We have been addressing several questions:

  • Are non-indigenous mammalian species (American beavers, muskrats, and American mink) interacting among themselves to amplify their impacts on biodiversity?

  • Which habitats are mink using and how that changes among seasons?

  • How do prey species adapt to the new predator and what is the impact that American mink predation has on native rodent and bird species?

  • Which areas of the Cape Horn Biosphere Reserve are suitable for further expansion of invasive species?

The synergistic trio

Three species are considered the most invasive and harmful: the American beaver (Castor canadensis), the muskrat (Ondatra zibethica), and the American mink (Neovison vison). These species, native to North America and Canada that naturally interact in their native range, are now creating an assemblage that have a large impact on the structure and functioning of the Magellanic Sub-Antarctic ecosystems.American beavers modify native forests along fast water streams into meadows with calm water, favoring the establishment of muskrats (0/+ interaction type). Muskrats are the main prey of mink that inhabit in the forests and meadows of the island, facilitating mink survival, especially during the winters (-/+ interaction type). In turn, mink affect native species of rodents and birds through predation (-/+ interaction type). 

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Mink niche expansion

We have showed that the American mink on Navarino Island shows a high occupancy (number of surveyed sites with mink present) during the summer, occupying forested areas away from the marine shoreline or even streams. Occupancy drops during the winter, with animals concentrating more closely to the shoreline during the spring. These results show that compared to the native and other invaded habitats, on Navarino Island mink frequently use more terrestrial habitats suggesting a niche expansion under new niche opportunities that may enhance the negative impacts of this predator on a myriad of small native vertebrates.

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(a) Google Earth (Google, CNES/Astrium) image of the northern slope of Navarino Island. (b, c, d) Camera-trap pictures showing the occurrence of mink in forests, high on the hill of the mountain and far away from rivers and the marine coast. (e) Mink tracks on the snow, where it is possible to observe the distance from the marine coast and the river at the end of the valley.

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Mink detections during four consecutive seasons: late summer 2014, winter 2014, spring 2014, and late summer 2015

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Such big teeth you have got!!

The American mink arrived to Navarino Island in the late 90s. Mink have no competitors or natural enemies on the island, establishing themselves as a new top terrestrial predator in this fragile ecosystem, where most prey species are naïve to this type of predation.

Potential mink impact on small native rodents

We conducted the first study on the two native rodents species that inhabit Navarino Island. We found evidence that rodents do not perceive mink cues as predation risk. These species are highly predated by mink, and this may explain the population declines we have observed in the recent years since the mink arrived to the island.

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We used field experiments and measured the Giving Up-Density that is the amount of food they left on a tray because animals perceive the site is too risky to continue feeding. Rodents seem to perceive open areas exposed to raptors as risky, but not areas with mink cues (i.e., mink gland odor).

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Potential mink impact on Magellanic Woodpeckers

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We collected evidence on the potential predatory pressure that mink can be putting on the Magellanic woodpeckers. We found evidence that woodpeckers are part of mink diet. We also found evidence with camera traps that woodpeckers forage quite frequently on the ground, making it more vulnerable to mink predation.

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Studying forest birds

We have described the breeding strategies of forest bird species for the first time. Among many interesting things, we found that passerine birds tend to nest close to ground level in the island, differently from continental populations of same species that build nests high in the trees.

We also studied the potential impact that mink can have on these bird populations. We found that mink are not representing a threat to passerine birds breeding in the forest, what is helpful to direct efforts to control mink where is more needed, along the marine coast.

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Invasive mammal expansion across the Cape Horn Biosphere Reserve

There are 11 species of non-native mammals inhabiting the Cape Horn Biosphere Reserve: on top of the mentioned beaver, muskrat and mink, there are free roaming horses, cows, pigs, dogs, cats, house mouse, brown rat, grey fox, and European rabbit.  We compiled information on 10 years of expeditions to update our knowledge on the distribution of these species.

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We also found that mink and introduced rodents are frequently unintentionally transported in vessels and that is likely the mechanism explaining the expansion of mink across this region of fiords and channels.

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We created an index of areas of potential further invasions. Thus, areas that present similar environmental conditions to those in which we know the species are present.

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Science to management

The different maps we have created are being utilized in the creation of National Park management plans: Cape Horn National Park, De Agostini National Park and Yendegaia National Park. Information on the potential distribution of invasive species and areas that could invade are critical for prioritizing control of their populations.

Reports for management

We summarize our main findings in reports for our partners in the local government and provide management recommendations aiming to help improve conservation in the region.

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We also provided technical support in the creation of the new marine park Cabo de Hornos - Diego Ramirez.

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Environmental philosophy: The eyes of the tree

We practice conservation in the Cape Horn Biosphere Reserve also from a environmental philosophical approach. 

Biocultural ethics, described by Ricardo Rozzi, extend the moral community to include other living organisms with which we co-inhabit this planet. Specifically, it advocates for the conservation of the habitats and the access to them by the community of co-inhabitants (humans and other-than-humans) as a condition of possibility for the continuation of their habits of life and wellbeing. The “3 Hs” of biocultural ethics: habitat, co-inhabitants, and habits.

 

We implement biocultural ethics through the Field Environmental Philosophy. 

This offers a methodological approach to integrate the biophysical, cultural and 

institutional dimensions through transdisciplinary actions of education and conservation. 

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The methodology consists on a cycle of four steps:

1) Interdisciplinary ecological and philosophical research

2) Composition of metaphors and communication through narratives 

3) Field activities guided with an ecological and ethical orientation 

4) Conservation in-situ. 

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With the invasive species work, we composed the metaphor "the eyes of the tree," which integrates scientific research with philosophy and Amerindian worldviews, and calls for conservation actions in a transdisciplinary mode.

Metaphors allow us to communicate concepts to the public by integrating ecological and philosophical studies through analogies that synthesize values and concepts in biocultural conservation and biocultural ethics.

In this case, the "co-inhabitant tree" has been equipped with a "techno-eye" that records the arrival of a new co-inhabitant, which exploits the ethical dilemma of how to co-inhabit and judge human behavior in this new relationship of co-habitation.

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In the metaphor of "the eyes of the tree", the "technological lens" (camera trap) allows us to expand our "conceptual and biocultural" lenses by generating an empathy with a tree, that is an old living witness of the processes of biocultural homogenization and the mink impact on the co-inhabitants of the forest. The technology used  is integrated with an Amerindian cosmovision (Koyukon culture) that conceives the ability of the trees to "observe". The empathy with the tree, generates an ethic with a holistic understanding of the ecosystem, looking to resolve the conflict generated by invasive species control plans, rooted in individualistic animal rights visions.

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More information about the Sub-Antarctic Biocultural Conservation Program can be found here: