Category: Post 7: Theoretical Perspectives

Blog Post 7: Theoretical Perspectives

The theoretical basis for my research project examines how varying levels of urbanization impacts bird species (especially seabirds) presence and abundance. To examine this, I’m collecting data on bird species presence and abundance (response variable) within three areas within Stanley Park that represent different levels of urbanization as determined by the percent cover of natural and anthropogenic habitat (explanatory variable).

Based on other research related to bird species presence and abundance along urban gradients (Tryjanowski et al, 2013) there theoretically should be a difference in the species richness and abundance between sites with the 3 levels of urbanization (West, South, East Lagoon). More particularly, the most urbanized sites should theoretically have the lowest species richness, and the most natural sites should theoretically have the highest species richness. It will be interesting to see where the results from my research align in this respect. While theoretically abundance should also be highest in more natural sites, previous studies (Tryjanowski et al, 2013) found that highly urbanized sites often have the highest overall abundance due to large flocks of a single species (Example, Large flocks of Seagulls and Crows near urbanized areas). Again, it will be interesting to see how my results compare to the other literature on the topic and if they align with the theoretical perspectives on bird species richness and abundance along urbanized gradients.

It is also important to think about how both species richness and natural habitat is examined and characterized. Theoretically, species richness includes all species, both native and non-native, but it might be beneficial to tease these categories apart. For example, if an intermediately urbanized site has the highest species richness but hosts exclusively non-native species then its value as bird habitat would likely not be comparable to natural areas where species richness might be lower but is dominated by native bird species. Additionally, when classifying habitat it is important to think about the impact native and non-native plant species play. While I won’t have the ability to examine these issues in my research project their theoretical impact on bird species presence and abundance, and the ways of evaluating overall richness and abundance do provide something to think about and will be mentioned in the final report.

Keywords: urbanization, Stanley park, bird species presence, bird species evenness, richness and abundance.

Citations

Tryjanowski, P., Sparks, T. H., Kuźniak, S., Czechowski, P., & Jerzak, L. (2013). Bird Migration Advances More Strongly in Urban Environments. PLOS ONE, 8(5), e63482. https://doi.org/10.1371/journal.pone.0063482

My research project is exploring the survival and maturation of rabbitbrush and sagebrush in Guerin Creek. Some of the underlying theoretical perspectives I will consider are water availability, interspecies competition, predation (herbivory), and disturbance-succession dynamics.

The water requirements of brush bushes and water availability at the creek site both interact to change germination rate, seedling establishment, and ultimately the maturation of brush bushes (McLendon et al. 2008).

Since both big sagebrush and green rabbitbrush bushes live together, they are in direct competition for space (access to sunlight), access to water sources, and pollinators (Young and Evans 1974). When examining my study area, there were clearly more big sagebrush than rabbitbrush in the creek valley. This was confirmed when analyzing my data and suggests that sagebrush is better adapted to life in the creek valley.

These two species are also subject to predation. Predators are similar between the two brush bushes including insects, grazing animals and rodents (Johnson 1979). Differential predation could influence the successful maturation of both brush plants, however in the literature I have reviewed, the predators are very similar for both plants. Because the brush bushes are extremely aromatic, most undulates do not graze on them, herbivores like deer and cattle are more likely to eat sagebrush over rabbitbrush, but consuming either in excess leads to significant decline in digestion.

Rabbitbrush is known to invade established sagebrush habitat following a disturbance such as a wildfire or construction, as it is much faster to grow from its underground roots (Young and Evans 1974). Sagebrush establishes more gradually following the disturbance. Research on the pre- and post-disturbance climax communities suggest that invasive grasses and plants lead to a significantly different composition in terms of vegetation following a disturbance. Because I was only able to see the mature plants, the species composition of the Guerin Creek ecosystem could not be measured.

Some interesting notes in performing the literature review for my project, I have found the research lacking specifically when looking at the water requirements for the brush bushes. In the reading I have completed, sagebrush and rabbitbrush are often considered pests, despite their significant ecological role in the stage-steppe ecosystems.

Keywords: Artemisia tridentata, depth to water (DTW), desert ecozone

References

Johnson, M. K. 1979. Foods of Primary Consumers on Cold Desert Shrub-Steppe of Southcentral Idaho. Journal of Range Management 32:365–368.

McLendon, T., P. J. Hubbard, and D. W. Martin. 2008. Partitioning the use of precipitation- and groundwater-derived moisture by vegetation in an arid ecosystem in California. Journal of Arid Environments 72:986–1001.

Young, J. A., and R. A. Evans. 1974. Population Dynamics of Green Rabbitbrush in Disturbed Big Sagebrush Communities. Journal of Range Management 27:127–132.

The theoretical basis of my project would be on how crows have adapted to anthropogenic effects. With most of the North Shore in Vancouver being developed, it’s interesting to look at the gradient from forested areas to fully developed areas and how crows utilize their new environment. One thing that my research focuses on is if there is a higher density of crows in the more developed area. Crows are very intelligent foragers, so the research is interested in if crows will utilize the easily accessible food. I believe that the crows will migrate to these more developed areas where the anthropogenic sources are the highest.

Keywords: Northwestern crow, urbanization, gradient analysis

The theoretical basis of my field project is that the response variable (stand density of maple trees) is influenced by a mature western cedar tree that dominates the site where observations are taking place. Ecological processes I may touch on include light availability, soil composition on western facing slopes in an ICH zone, influence of invasive groundcover that is present on the site, influence of litter as there is a thick blanket of maple leaves present on the site, impacts on the site from the rocks and boulders that are present, and the response of the maple trees to changes in canopy density as determined by the large cedar.

3 keywords or phrases that could be used to describe my project are: Acer glabrum, stand density, and forest ecology.

Post 7. Theoretical Perspectives.

I am comparing vegetation growth between dead wood (nurse logs) and the ground. I believe plants growth does better on the wood than on the ground. As for “why”, that probably varies from log to log. All the logs have the advantage of providing nutrients and holding moisture. In some places people walk on the ground but not on the log, so only plants on the ground are trampled. Animals such as deer may come along and forage on the plants at their level on the ground but are not able to reach plants on tall stumps. Some areas have plants that may shade out new plants attempting to germinate. Seeds that land on the stumps and logs are above the level of these competitors. In one spot there was a steep slope that nothing was growing on, except plants on a stump sticking out of the side of this hill.

Keywords: nurse logs, stumps, new plant growth

The overall theoretical basis of my research project is ultimately how different species are distributed in a community park, when there are various influential factors, such as sunlight, human disturbances, landscaping, etc. Based on the results that I have obtained and the research that I have done, it is evident that different species require different conditions in order to grow, survive, and reproduce, and as such, the abundance, and percentage coverage will vary depending on the species. I expected that all of the species would be mostly distributed in areas with high sun exposure, but upon analysis of the results, this is not always the case. Although sun exposure, is not the only factor influencing where a species is present, it is an important factor. As such, I chose to examine sites from a forest (more shade), near a pond (more moist and sun exposure), and the other side of this pond (more grass and sun exposure). I chose these sites in order to compare the influence of sun exposure, and moistness.

Three keywords that could be used to describe my research project are: species distribution, species abundance, and sun exposure.