Coevolution of Plant Animals: A Study of the Coevolution of Herbivores and GrassesIntroductionCoevolution can be defined as an evolutionary change in a trait of individuals in a population in response to a trait of individuals of a second population, followed by an evolutionary response of the second population to the change in the first (Janzel, 1980). Coevolution of plants and animals is a very broad topic with many different areas and examples, so this essay will focus on the evidence for coevolution between grasses and herbivores. Key questions explored will be how coevolution is studied, deciding whether it is coevolution or whether it is related to other factors. It is important to note that not all forms of interaction, mutualism or symbiosis are synonymous with coevolution. It is easy to believe that all mutualistic relationships are due to coevolution, for example animal seed dispersal, but this is not always the case because the animal may have entered the plant's habitat with needs previous diets and have just started to feed on the fruits of the plant. species that suited it best (Janzel, 1980). So how do we determine if this is in fact coevolution? This is done through careful observation, experimentation and phylogenetic analysis. When observing a potential coevolutionary phenomenon, it is important to ensure that the response between species is indeed reciprocal and not due to environmental factors such as climate, nutrients or pH. Experimentation is a useful way to test whether an adaptation is due to an environmental factor, another influence, or the species in question. The researchers will study the same interspecific interaction in a number of different communities and continue their experiments over a long period of time to obtain...... middle of paper ...... each of these rosettes produces a flower stem. This can increase its seed production up to 3 times more than those without multiple stems (Inouye, 1982). This would suggest a mutualistic relationship between lepidopteran larvae and Jurinea mollis. Owen and Wiegert have published several papers hypothesizing mutualism, what they argue is that the grass-herbivore relationship is not a simple predator-prey relationship, because grasses can be eaten without being killed. They challenge the assumption that being eaten is a bad thing and suggest that grazing actually extends the lifespan of grass (Owen and Wiegert, 1982). However, there is evidence indicating plant defenses against herbivores, primarily the presence of silica which increases foliage abrasiveness and reduces foliage digestibility, in turn reducing herbivore performance (Massey et al.., 2006).