The paper discusses the long term effects of the loss of higher predators on the ecosystem. The present high rate of extinction is largely effecting predators and the paper suggests that the loss of these species has a significant long lasting effect on the future evolution of surviving organisms. The loss of predators in an ecosystem cascade down the food web effecting all of the species interactions in an ecosystem. The result of this “trophic downgrade” is an alternative stable state in an ecosystem.
Trophic downgrading is cryptic because the resulting effect of losing the apex species is not entirely clear until that species is gone. It is also difficult to conduct a study of these effects as often the species studied inhabits large range spaces and as such effects a larger area than can reasonably be controlled in any study and influence the change in the ecosystem across impractical time scales.
The paper goes on to discuss that despite difficulties in artificially testing these species interactions strong evidence is present in the real world of the effects of extinction or extirpation of apex species from an ecosystem. On short time scales immediate evidence can be seen in some ecosystems for the reduction of certain herbivores. The loss of these predators resulted in a increase in herbivory which reduced the availability of food for herbivores which were already free of predators.
The paper then goes on to list the effects of ecosystem reorganization due to trophic downgrading. These effects include increasing wildfires, increasing disease transmission, chemical changes in soil and water, increased risk from invasive species and decrease in overall biodiversity.
1. Can you think of a viable experiment than could show a top down cascade on an ecosystem? What problems would you face?
2. Give an example of an ecosystem effect caused by the loss of a predator species. is there an instance where the loss of a native species could be a good thing for biodiversity?
3. How do you think the loss of many predator species will impact future evolution after the next mass extinction?
4. Which do think is more important to ecosystem stability? Bottom up effect or top down trophic effects?