For my community ecology class, we read a paper regarding
the ecological meltdown of multiple predator-free islands created via a
hydroelectric plant in Venezuela. No top predators reside here, as the islands
are separated from the rest of the tropical forest surrounding them. This has left only predators of
invertebrates, seed predators, and herbivores. The effects have been extremely noticeable and have begun to
create completely different communities from the ones found on mainland close
by.
The
lack of vertebrate predators has caused for the density of herbivores to
skyrocket to 10-100 times greater than can be found in the mainland
forests. Due to this high number,
it is believed that top predators are key in limiting herbivore populations on
the mainland. These herbivores
have done extensive damage to the local populations of seedlings and saplings
from the canopy trees.
While
these species are usually maintained via top-down regulation, the lack of
species above them on the food chain has enabled their populations to grow at
exponential rates. This will most
likely occur until they become restricted again, this time via bottom-up
regulation. Eventually, the populations
will be so large that the amount of vegetation currently on the island won’t be
enough to maintain them. Depending
on how rapid this transition is, it is possible that some of these species will
undergo the bottleneck effect.
This can be devastating to a species, as it is usually accompanied by a
large loss of genetic diversity.
These
island communities are completely circumstantial and don’t provide much
information in terms of successional processes in the tropical rainforest. That being said, they do provide an
extremely interesting look at how the removal of any given species can cause
widespread changes to an ecosystem.
It will also be interesting to see how the transition into bottom-up regulation
takes place and whether it is as drastic as it has the potential to be.
paper:
http://www.uvm.edu/~ngotelli/Bio%20264/Terborgh.pdf
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