A Comparison of the Effect of Species Diversity on Plant Abundance

Hypothesis: As species diversity decreases, plant abundance decreases because of more intraspecific competition. If different species required different resources, then an ecosystem that contained the same specie would have more competition for the same resources. This would cause resources to become limited and contribute to a smaller plant abundance. Predictions: 1.) As species diversity increases, there will be an increase in reproduction rates (because there would be more resources for plants to thrive to maturity) 2.) As species diversity increases, plant abundance will increase (because there would be less intraspecific competition) 3.) As species diversity increases, there would be less dead and wilting plants (because there would be more resources for the species to develop and sustain life) Variables: Four variables were used: the number of different species, vegetation coverage, grass coverage and plant abundance. All variables are quantitative data. The number of different species and plant abundance are both discrete data. The former variable was counted for based on morphological features of the shape of the plants' leaf. When in disagreement about two plants, they were counted as the same species. The latter variable was an estimation based on 1/4^thof the quadrat. For both variables, species number and plant abundance included those that fell above the quadrat even if their roots were not within the quadrat. Vegetation coverage and grass coverage was a percent estimation based on the entire quadrat from a bird's eye view. They are both continuous data using an interval scale of 0 to 100%. If soil could not be seen within the quadrat then vegetation coverage was considered to be 100%. Methods: A field study was conducted at the grasslands located at York Boulevard and Steeles Avenue on the York University Keele campus. Data was collected in groups of four with Bonnie Chan, Charlie West, Raza Shahid and Misha Ditmans. The group was split into pairs each with a quadrat: one headed east and the other headed south. The goal is not to cluster around the same region. Both pairs started in the middle of the grassland and extended out. A total of 25 samples were collected. To ensure random and consistent samples, the quadrats were placed every five steps from its prior location. For efficiency, the number of plants/abundance was collected based on 1/4^th of the quadrat: to represent the quadrat as a whole, that number would be multiplied by 4. The other three variables, were collected based on the entire quadrat. If a plant fell above the quadrant but its roots were not in the quadrat, it was still counted for. If there was a confusion on whether two plants were of different species, it was assumed that they were the same: the plants were differentiated based on morphological leaf structure. Vegetation and grass coverage was recorded as a percent. One person would record and the other would collect the data. This was a preventative measure for inconsistencies as measurements can be subjective (e.g., a 65% grass coverage might be viewed as a 80% coverage to someone else). The data was collected under sunny and humid conditions and later compiled to form 25 samples: 12 from one pair and 13 from the other.