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Original Paper: Vickers, T. W. et al. 2015. Survival and mortality of pumas (Puma concolor) in a fragmented, urbanizing landscape. PLoS One 10(7): e0131490.

Habitat destruction and exploitation as a result of human activities have led to the extinction of many species. One species that is now endangered is the large cat called the puma or cougar (Puma concolor). Threats to pumas in southern California include habitat loss, habitat fragmentation, and conflicts with humans, which cause population declines, isolation, and ultimately smaller gene pools for the puma.

Two small puma populations occur in southern California between Los Angeles and San Diego. Earlier studies showed that pumas in both populations had very low genetic diversity, and little or no breeding occurred across populations. The populations are separated by urban and suburban areas, including highways, forming a barrier between the Santa Ana Mountains in the west (the more developed area) and the Peninsular Range to the east. Occasionally, however, pumas have been found to travel through agricultural areas, especially in the Peninsular Range.

Scientists fitted pumas in these populations with radio collars to track them and generate data on survivorship and causes of mortality, with the hope of conserving the populations (see figure). Between 2001 and 2013 they captured, marked, and monitored 74 animals in the two populations. Thirty-one marked animals came from the Santa Ana Mountains and 43 from the Peninsular Range. During the course of the study, 36 of the marked animals died. The table shows the causes of mortality in this sample.

Questions

Question 1

Vehicle collisions and hunting, both legal and illegal, are the two known major causes of puma deaths in these populations. Suspected and confirmed diseases together rank as the third most common cause. The two major causes result from human actions, particularly loss of habitat and/or habitat degradation, which forces pumas into urban and suburban areas. Disease is presumably a natural cause.

Question 2

As effective population size decreases, a population enters an “extinction vortex,” decreasing more every year and becoming more likely to go extinct. The pumas are living in an increasingly urban area and are at risk from vehicle collisions, hunting (both legal and illegal), and other urban-based factors, in addition to natural risks. As their population size declines, their genetic diversity also declines, making successful reproduction less likely. These factors suggest that, without some kind of intervention, pumas in these two populations will soon go extinct (with the Santa Ana population dying out first).

Question 3

Maintaining any population and saving it from loss or extinction contributes to biodiversity, because all species and populations are part of biodiversity. Each lost population represents the loss of a strand in the web of life, which is connected to other strands (species) in the community. The puma, as a top predator, contributes to control of its prey populations, which in turn affects lower levels in the food chain, down to producers. Loss of the puma could therefore affect community structure at several levels. This in turn will limit the effectiveness of ecosystem functions and the ecological services (both practical and aesthetic) provided by California ecosystems.

Question 4

Both populations are very small, so it makes sense to maximize the size of the gene pool by attempting to conserve both populations. However, finding an appropriate protected area might skew the protection toward one population: the less urbanized Peninsular Range population. If a protected area is identified in the Peninsular Range, habitat corridors could be provided to connect this population with the Santa Ana population, thus extending protection to both populations.

Question 5

In a coupled human-natural system, humans in urban and suburban areas are enlisted to increase biodiversity in their own habitats. For small species (such as pollinators), people can plant native gardens or even window boxes. This is more difficult, but still possible, for large top predators, such as pumas, with large geographic ranges. If conservationists establish a protected area for pumas in the Peninsular Range, a fairly large buffer zone would need to be established around it. The buffer zone would involve agricultural areas, and farmers would need to help maintain it. This would involve an extensive education program, since many farmers see pumas as “the enemy. ” (In fact, the legal hunting that causes many puma deaths results from pumas feeding on livestock after being forced out of their natural habitat.) Farmers could be encouraged to establish edge habitats on their properties, allowing pumas safe passage to wilder areas. Coupled human-natural systems friendly to pumas would be more difficult to establish in urban areas, but wildlife corridors—particularly those allowing safe passage across highways—would be one obvious example.