Loss of Cougars Spirals Entire Ecosystem Downward

The front page of today's San Francisco Chronicle features a sobering story by David Perlman on how the decline of cougars at California's Yosemite Valley has dramatically changed the park's ecology. A recent study on the matter was led by Oregon State's William Ripple and is published in the latest Biological Conservation.

The downfall of cougars at Yosemite began in the 1920's, when hunters were brought in to shoot the wild cat predators to keep the growing number of human visitors safe. Cougars are stunningly majestic creatures that are also sometimes referred to as mountain lions or pumas. I once met a cougar face to face years ago on a state park road. He looked beautiful, emaciated, and desperate for food and water. I could almost sense him begging me for food. Thinking about it saddens me to this day. I'm grateful he didn't choose to eat me.

The drop in cougar numbers at Yosemite then led to a large increase in the park's mule deer population.

The deer consume all sorts of vegetation, including black oak seedlings. When mule deer numbers are kept in check by their cougar predators, the deer serve as nature's gardeners, preventing certain plants from overtaking areas and mowing down overgrown patches. With an excess deer population at Yosemite, however, black oak trees started to disappear.

Fewer black oak trees then changed the way that ponderosa pine seedlings took root in the park. Yosemite wound up experiencing a ponderosa pine invasion.

Since the trees help to determine the surrounding plant growth, the lack of black oaks also led to a decline in some of the park's most colorful and fragrant flowers, such as evening primroses.

The roses, in turn, affect insect species, which serve as food for local birds and on and on. You can see the point that a disturbance to one key member of an ecosystem can throw a region's entire ecology out of balance. Thankfully cougars aren't as threatened in other locations, so our own Animal Planet filmmakers were able to capture the below footage illustrating the big cat's hunting prowess.

Comments

[Bpaul]

Good catch, and nicely handled.

Bp

[Graham Cliff]

This article remarks that insects may be in decline and hence primroses will suffer. So too will the creatures which feed on insects.
Insects have been in decline for years but only now are people beginning to realise. The species decline of flora, invertebrates and subsequently small insectivores was made as long ago as May 1994. On-one was listening then and no-one is listening now. We really will be JTL?

[Colin Henshaw]

This is a classic example of the concomitant effects of what happens when one trophic level is pulled out of the equation. We are seeing this in urban areas with insects. Many habitats adjacent to conurbations in many countries have seen a decline in insect diversity over the past forty or fifty years. This mirrors the expansion of lighting over the same period as the twenty-four hour day increasingly prevailed throughout our communities. Lights of all kinds attract insects which, if not killed outright by the high temperatures, will spiral around them till they drop, too tired either to feed or to procreate. With this having gone unnoticed for years, insect populations declined. As a result environmental organisations observed declines in common species of all kinds - birds, bats and other small mammals, spiders, reptiles and amphibians, all of which are dependent on insects in one way or another. With insect numbers declining, so will the number of successful pollinations, resulting in reduced plant diversity, and further exacerbating the already declining insect populations. This can ultimately affect us as it will affect crop production. The situation will only improve if we change our attitudes towards energy usage, especially lighting at night. It should only be used sparingly, when needed, where needed, and in the correct amounts.

[Jen Viegas]

Thanks to both Bpaul and to Graham for their comments. I never thought about the light/insect decline connection, but now that you've brought it to my attention, I'll be on the lookout for related studies. What you say certainly makes sense. Our artificial lighting does completely change the environment, especially at night.