Species go extinct. It is a fact of life. 98% of the species that have ever existed on Earth are now gone forever. However, conservation biologists believe that we are currently in what is called a mass extinction event. This event is not as dramatic as the extinction event that saw the end of the dinosaurs or the one at the end of the Permian period, which killed off 96% of the species present on Earth at that time. But it is no less deadly. And this time, it is not an asteroid that is the cause. Directly or indirectly, the cause of this extinction event is us.
How do we save species from extinction, with limited resources and time? The answer might be surrogate species.
By attempting to conserve a certain species or a suite of species, other species and/or habitat that is in some way connected to the selected species(s) might be conserved as well. That is the power of surrogate species; they represent other species and their needs. At least, that’s the theory. There are multiple roles surrogate species can play: umbrella, indicator, flagship… In many cases, surrogate species do help to protect biodiversity, but not very well.
Carnivores, in particular apex predators, have the potential to be useful surrogates.
- Carnivores tend to need large areas to live in, because they need tons of prey, which need tons of space and food. It is assumed that a protected area that is large enough to sustain a population of an apex predator should sustain viable populations of other species. Bam, a sturdy umbrella.
- Apex predators are generally the first species to come into conflict with humans. This leads to them being sensitive to habitat loss and human activity, which makes apex predators potentially useful as indicators of human influence on the landscape.
In addition, carnivores eat other animals. By doing what they naturally do, they are able to regulate other species’ populations. Sometimes, the fear of being eaten is so strong that prey species act differently if there are predators in the same area, or if they remember predators being in the area in the past. While not a surrogate role, the regulation of other species makes carnivores an important link in the ecological community.
Madagascar is home to the endemic carnivore family, Eupleridae.
There are nine carnivore species, all of which have different dietary and habitat needs. All the carnivores are currently threatened but not much is known about them, especially within the eastern rainforests. As an example of how little is known about them, just recently Durrell’s vontsira (Salanoia durrelli) was discovered in the Lac Alaotra marshes of eastern Madagascar. Finding new species is uncommon; finding an un-described carnivore is almost unheard of.
Madagascar’s native apex predator is the fossa, a creature with a ferocious reputation. Despite being described as “puma-like”, it is perhaps the size of a small-to-medium sized dog.
It can be found throughout Madagascar where ever there is forest, although it is uncommon. The fossa is the only predator in Madagascar capable of preying on the adults of all lemurs, including the indri, which can get to the size of a small child. Originally, it was thought that the fossa specialized in eating lemurs, but studies have shown that fossa aren’t picky. Fossa will eat anything—crabs, tenrecs, snakes, birds, frogs…even other carnivores. And fossa are rapacious; in one recorded instance, they essentially ate diademed sifaka (Propithecus diadema) out of a fragmented patch of forest. Of course, lemur behavior is significantly influenced by the presence (or absence) of fossa, and they have to be on alert from fossa 24 hours a day, since fossa can be active at any time of the day.
There is a lot of evidence that fossa strongly influence other species’ populations and behavior. But how can a small cat-like weasel with an enormous appetite save Madagascar’s other species? Certainly, if it is not already a flagship species, then it has the potential to be one, although perhaps not as popular as the ring-tailed lemur (Lemur catta). It is perhaps the only Malagasy carnivore relatively well-known in American and European zoos, it was the villain in Disney’s animated film Madagascar and it is also the subject of a T-shirt line available in Antananarivo, the capital city of Madagascar. Let me make a case for three surrogate roles:
Fossa as a biodiversity indicator: Apex predators require a large number of potential prey species, which allows for prey-switching in times of hardship (think of keeping your refrigerator stocked with many different types of food just in case you run out of your favorite). These prey species in turn would potentially have diverse requirements, implying ecosystem complexity. Because the fossa’s diet seems to depend on prey abundance, they may switch prey in times when their main prey becomes scarce. This in turn would mean that a healthy fossa population would require either a sizable number of prey species or one extremely common species. Because their prey base is so varied (encompassing small frogs to large lemurs), this would suggest that fossa might be used as biodiversity indicators in areas that do not have one species that is overly abundant.
Fossa as an umbrella species: GPS satellite-collared fossa in Kirindy Forest (western Madagascar) had home ranges in size from 21-77 km2. Although there have been few studies on fossa home range, and what studies that have been done are based on scant data, it is likely that fossa have relatively large home ranges for their body size. Given the large areas required by fossa, they may serve as useful umbrella species for the conservation of other species. If national parks and protected areas focus on sustaining viable fossa populations, they should protect enough area to provide for other species.
Fossa as a sentinel: Sentinel species are loosely defined as “condition indicators”: species that researchers can monitor to track ecosystem dysfunction, much like the canary in the coal mine. Apex predators can be especially sensitive to ecosystem dysfunction, often being the first to go extinct in an ecosystem and being sensitive to human influences on the landscape. Fossa tend to be very rare in fragmented forests, and entirely absent from highly degraded forests. There is little information on how fossa are affected by human activity, habitat disturbance and other symptoms of ecosystem dysfunction, but it is entirely possible that they can be a useful sentinel.
Madagascar’s conservation challenges epitomize the worldwide urgent need to protect as many species as possible with limited resources. Along with understanding basic fossa ecology, I am interested in exploring in what ways the fossa might be a useful surrogate species in the eastern rainforest ecosystem. Fossa can strongly influence prey populations and prey behavior. The fossa’s need for a large prey base and large areas over which to roam could make it fit well into the surrogate roles of biodiversity indicator and umbrella species. Whether it is sensitive enough to habitat fragmentation, human activity and other ecosystem disturbances will determine whether it can be used as a sentinel species. But this is all theory. We still need the evidence to back it up, or at least strengthen the case. That’s where I hope to come in.
My goal is to further the conservation of Madagascar’s apex predator and overall biodiversity by providing the first estimates of fossa density in northeastern Madagascar and examining the effects habitat loss/degradation, human activity, and exotic species on fossa, lemurs and other species that we catch on camera traps. To do this, I will:
1. Estimate fossa density in Makira, determine what factors influence fossa density and gather evidence to determine whether fossa can be useful as an umbrella species, a sentinel or a biodiversity indicator.
2. Examine relationships between species richness and the ecological community structure at seven sites to fossa density, habitat loss/degradation, human activity and the presence of exotic species.
While they kill other animals, carnivores might be able to actually help in the fight for conservation. Fossa are the animal equivalent of a black hole. And I want to determine how many of these roving black holes there are in Makira. But where exactly is Makira, and where are we getting this data that I’m going to use? Check out the next page, Akaiza (Where)? for the next installment!