Theepika Nagalinam
Biology 1610 Lab
07.15.2013
Food- Web Models Predict Species Abundances in Response to Habitat
Change
Introduction
Habitat loss is a big threatening issue to the living organisms which always affect the top predator, prey
and competitors in the food web. We have to understand the deep reason behind the population size.
Anyhow, the researchers said that it is really hard to determine the population size by just looking into
the habitat area. Species abundance can determine by the trophic structure accurately than the habitat
area. Nicholas J. Gotelli and Aaron M. Ellison did an experiment to prove their hypothesis by making a
study in pitcher plant (Sarracenia purpurea).
There are two types of models which predict the habitat alternation. Single factor modeling includes
keystone effect where single factor controlled the population size. The other model is food we includes
top- down and bottom- up process where the energy transfer from one food chain to the other.
Materials and Methods
During the experiment they manipulated the habitat volume by changing the water level in pitcher plant
and eliminated the larvae from the dipterans in order to make the trophic structure easy. Whenever the
leaf is open, they counted abundance of taxon for the food web. They measured the volume of water
and the number of dipterans larvae during every treatment. The food web model and single factor
model charted orthogonally with three groupings which are food web components which have no link
between volume, partial volume model and full volume model.
Result
They selected about 50 pitcher plants at northeastern Vermont, United States. This plant maintains the
aquatic food web by storing water in it. Furthermore, it gets nutrients by capturing the prey.
The arthropods such as ants, aphids, beetles, butterflies and cicadas trap into the pitcher plant and the
midges (Metriocnemus knabi) and Sacrcophagid fly (Fletcherimyia fletcheri) larvae consume the
arthropods. Then the shredded insects break down by bacteria and consumed by protozoa. Then the
larvae consumed bacteria.
Discussion
Wyeomyia keystone model showed the essential of the trophic structure in species abundance. This
model showed that mosquito larvae prey on rotifers and sarcophagid fly. At the same time food web
model also showed the importance of trophic structure where protozoa affected the mosquito and mite
affected the rotifers. Spices abundance of food web can be determine by the trophic structure though
the manipulation changed the habitat volume totally. The article states “the importances of trophic
interaction that have been observed have been altered by an invasive species.” Over all the researchers
proved that trophic structure play an important role in species abundance and habitat area is not only
enough to find the alternation in population size.
Gotelli, Nicholas J. and Aaron M. Ellison. 2006. Food-Web Models Predict Species Abundances in
Response to Habitat Change. PLoS Biology 4(10): e324.