Sometimes simple things take on an entirely new facet when you delve deep in it. This is exactly what happened when scientists took a deep scan of the predator-prey relationship with emphasis on loss of predators in an ecosystem. They have come up some facts that are akin to fiction.
It is an established fact that predators control populations of prey animals, but the latest studies show that there is much more than what meets the eye. It has come to light that apex predators also control smaller predators (mesopredators), and render invaluable ecosystem services like protecting river banks from erosion and providing nutrient hotspots.
This slew of latest information has come from the research by Euan G. Ritchie, Beschta, R.L, Bump, J.K. et al and is very germane in areas where top predators are disappearing and hold lot of portents for us in India against the backdrop of disappearance of tigers.
Where apex predators become extinct, mesopredators move to the apex and practice what apex predators were doing. In stark contrast to the skills of the apex predators the mesopredators do not possess, an identical mix of honed hunting habits and skills. This topsy-turvy situation brings in cascading effects on the ecosystem, the full implications of which are being now unraveled and it makes fascinating reading.
Researchers Euan G. Ritchie and Christopher N. Johnson have contoured two ways in which top predators impact lesser mesopredators. These factors are what they call loathing and Fear .Top predators loathe mesopredators and have a natural tendency to exterminate them. Scientists say perceived competition could be a factor that makes them seek out mesopredators and kill them. This in turn leads to reduction in the abundance of mesopredators. Fear is another key that plays key role. Studies have demonstrated that fear of apex predators can engender behavioral shifts in mesopredators. Fear may also cause mesopredators to reduce or change their times of activity and shift in their habitat preferences. This in turn can lead to the reduced ability of mesopredators to find food, directly impacting and lowering reproduction and survival.
An interesting scenario unfolds where the behavior of top predators actually aids the survival of certain prey species. By keeping a constant check on mesopredators, top predators in turn become protectors of prey species, especially smaller prey. The researchers say it won’t be outlandish to call the world’s top predators 'guardians of small prey species'.
A reduction in top predators allows mesopredators to increase disproportionately. Research indicates that sometimes this could be as much as fourfold. The mesopredators with a high reproductive rate when compared to larger predators can quickly increase in abundance and drive prey species to extinction. Even if large predators also occasionally eat the same prey species as mesopredators, their impact is lower due to their larger territories and smaller overall population sizes.
The decline or extirpation of top predators can have drastic impacts on plant community also. The removal of top predators from landscapes reduces predation and ensuing predation risk. Untrammeled foraging by large herbivores that ensues, leads to heavy utilization of plants by these animals. Over time this can alter the very composition of plant communities and thus impact other animals that are dependent upon these plants. Local extinction of certain plants is also a distinct possibility.
Scientist who did a detailed analysis of five parks in USA found that, twenty years after top predators were displaced, tree recruitment declined to 10 percent of the number required for maintaining historical tree communities. An analysis of data over a period fifty years demonstrated effects, which were even more pronounced. The recruitment levels had dropped to 1 percent. Eventually this trend would lead to local extinction of many native trees.
The decline in surviving trees and the loss of particular species of plants due to predator loss can have ripple effects on the ecosystem. Accelerated erosion of hill-slope soils or of stream banks can occur as the diversity and biomass of plant communities gets affected. The loss of top predators can also have massive impacts on aquatic environments, including altering and degrading plant communities .This could lead to a situation where the plant community may be no longer capable of maintaining stable stream banks during periods of high water flow.
One of the surprising discoveries was that through hunting, the apex predators actually create nutrient hotspots that keep ecosystems rich and varied by enriching the soil with biochemicals. The scientists found that the soils of kill-sites were 100 to 600 percent richer in inorganic nitrogen, phosphorous, and potassium than control sites. In addition the area had abundance of bacterial and fungal fatty acids also. Nitrogen levels in foliage at kill-sites were 25 to 47 percent higher than control sites.
Nature works in myriad ways. We have only scratched the surface. The cascading effect of loss of predators is one such example. This should be an eye opener for our wildlife manger.