Ecology Lab Report

Ecology Lab Report


The study is an evaluation of the relationship between insect abundance and bird abundance in grassland and woodlot habitats. The study uses transects and quadrats in sampling the quantity of different bird and insect species within the two habitats. The results confirmed the hypothesis that higher insect abundance results in higher bird abundance. Also, results point to a higher abundance of both birds and insects in grasslands compared to woodlots. Although the composition of birds and insects is dependent on a myriad of factors, both biotic and abiotic, the results conclude that there is a positive correlation between the two variables.


The number of observed individuals of a specific species with in a community is best described through abundance distribution. Consequently, a species abundance distribution is the most common descriptions of any ecological community (1). This paper aims at determining the effect of insect abundance on bird abundance within a specific geographic location. As thus, the paper hypothesizes that insect abundance has a positive effect on bird abundance.

In carrying out the experiment, two types of habitats were examined that is grasslands and woodlots. Data from the two habitats was analyzed and compared in making an empirical conclusion. In this study, the prediction was that a positive relationship would result in higher bird abundance in areas with higher insect abundance since insects attract birds that prey on them. In addition, a positive relationship would mean that areas with higher bird abundance have higher biological productivity since insects live on vegetation and some birds are herbivores.


The methodology in use was based on quadrats and transects in sampling the number of individuals in different bird species as well as the number of insect species. Data was collected in two habitat types of woodlot and grassland. The study used ten quadrats of one square meter each to ascertain the insect divert in the two habitats. These quadrats were randomly placed at ten different locations within a habitat and all the species identified in each one counted. A similar approach was used in randomly placing ten transects at different locations to ascertain the different bird species. The counting was conducted with the help of a telescope after walking for 25 meters from the transect spot.


The study found that grasslands had bigger amounts of both insects and birds compared to woodlots (Figure 1). Also, independent t-tests done on each of the two variables indicate that the mean abundance for both insect and bird are not significantly different in the two habitats. In essence, therefore, the means of both birds and insects in the two habitats were almost similar.


A higher abundance of insects within a habitat results into a higher abundance of birds within the habitat. Results in the study pointed out that the number of birds within the two habitats under study was proportional to the abundance of insects in the respective habitats.  Also, more birds and insects were observed in grasslands that in woodlots. These results serve to qualify the prediction made in the introduction that a positive relationship would translate into higher bird abundance in areas with higher insect abundance. Indeed, results from the study have positive implications on the study of bird populations and migration patterns.

An interpretation of the correlation coefficient explains the relationship between insect abundance and bird abundance. Although relatively small, the true correlation coefficient of 0.549 points to a positive correlation between the two variables. The significant value of 0.06 is higher than 0.01 communicating a higher significance and a stronger and positive correlation between the birds and the insects.

While some bird species feed on insects, they also prey on a large number of invertebrates thus resulting in an increase in the number of insects (2). Studies have observed t6hat birds within grasslands have better diets as well as habitats as opposed to those inhabiting forests and woodlands. The grassland is more expansive compared to the woodlot and therefore beneficial to both birds and insects. The rationale behind this advantage is that open grassland permit higher solar radiation making them warmer and beneficial. Also, birds are better predators in the open as the prey does not have many opportunities to hide.

A greater diversity of insect species will subsequently yield greater diversity in bird species, in addition to greater numbers of those birds (3). The basis for our prediction is that high diversity in insect species not only attracts more birds which consume them, but is also indicative of a healthier habitat and favorable biotic (i.e., health and variety of vegetation) and abiotic living conditions (i.e., wind speed) to support a broader spectrum of species both insect and bird. Also, species of birds that do not directly prey on insects will be attracted to these areas as well. If the environment varies in some way, the species that are specialized to those variations should be found there, allowing more species to exist in an area as the variation increases. Variation provides the new niches for species. For variations in space, such as bare rock or marshy areas, specialized species will be found in those areas.

Lastly, random chance can play a very important role in determining composition and abundance in an ecosystem. An insect species that is specialized on a particular host plant will usually go extinct if the host species does, no matter how well-adapted and otherwise successful it is. If the insect had lived on another plant species, it would not have gone extinct.



Williams PH and Gaston KJ. 1994. Measuring more of diversity: can higher-taxon richness predict wholesale species richness?. Biol Conserv. 67(3): 211-217.

Sipura, M.. 1999. Tritrophic Interactions: Willows, Herbivorous Insects and Insectivorous Birds. Oecologia, 121: 537-545.

Murakami, M., and Nakano, S.. 2002. Indirect Effect of Aquatic Insect Emergence on a Terrestrial Insect Population Through by Birds Predation. Ecology Letters, 5(3): 333-337.

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