THE DENSITY-DEPENDENT OUTCOMES OF COMPETITION WITH A. FATUA AND E. CALIFORNICA

Marilyn Ong

California State University East Bay
Biology 3110 Lab 1A
Professor Thomas Gabel
April 11, 2015
Introduction
A plants’ density is the amount of space that remains between plants in a given area. Such density influences the growth and yield of the individual plants involved. The effects of density may also vary when one or more species are planted together or by themselves. When two plant species are grown together and are competing for the same resources this is known as interspecific competition. When a plant species is grown by itself and its members are competing with each other for resources this is known as intraspecific competition. According to an article published by J. Connolly when two species are competing interspecifically their initial interference with one another will depend on each species shoot architecture and utilization of above-ground resources. He discusses that as plants age the competition depends less on shoot architecture and more on the varying treatment conditions. The results of his study were that both the barley and wild oat species interspecific competition were regulated more by plant height during the early growth stage and dry matter accumulation than any other factors. Meaning that the interspecific outcome will vary depending on the density and identities of individuals in each treatment, as well as the nutrient environment in which they grow (Connolly, 513). In terms of intraspecific competition while resources are limited as a population grows the availability for such resources will decrease thus growth rate will slow down as intraspecific competition increases. This makes intraspecific competition negatively density dependent. Additionally, a study performed by Don W. Morishita suggested that the effects of intraspecific competition amongst members of the same species will vary from species to species yet intraspecific competition will be greater than interspecific competition. She discovered this when her results showed that wild oat plants alone and barley plants in mixture obtained the largest biomass plant-1 in both of her experiments.
In regards to our laboratory study, the effects of interspecific and intraspecific competition amongst weedy plants Avena fatua and Eschscholzia californica will be evaluated at the end of a seven week growth period in a greenhouse. Competition over water, space, light, and soil nutrients will lead to outcomes that are density-dependent and such result will be measured by total biomass of shoot tissue in each plant species. Both A. fatua and E. californica germinate rapidly and are potentially invasive species which make them ideal candidates for growth evaluation over a relatively short period of time. A. fatua, also known as the wild oat, is an annual grass adapted best to the cool seasons in California and is known to be somewhat of a nuisance amongst the agricultural weeds. E. californica, or the California poppy flowers annually and is known to be invasive to the United states. It is likely that both species grown intraspecifically will result in a higher biomass in a lower plant density treatment than in a higher plant density treatment because intraspecific competition leads to decreased rates of resource intake and ultimately a decrease in individual growth and development. Thus the more individuals the less resources, and less reproductive success.Yet when grown interspecifically I predict that A. fatua will have a higher biomass yield in the greater plant density treatments because A. fatua has a higher threshold for excessive sowing than E. californica and a tendency towards aggression. However in the treatments with lower plant densities interspecific competition will result with a higher biomass yield of E. californica because of its greater initial growth that is due to its ability to exist in a drought tolerant environment