they evolve no mechanisms for strong competitive ability. On the other hand, K selected species exist under both intraspecific and interspecific competition pressures and therefore do develop a strong mechanism for competitive ability. R-selected life history can be characteristic of many plants while K-selected life history is characteristic of humans or other mammals. Test 3 Material What are the impacts of herbivory? Discuss the structural and chemical defenses seen in plants and provide examples. When is herbivory considered predation?
Herbivory is an interaction in which herbivores feed on autotrophs (Plants). A true predator kills its prey but in most circumstances, besides phytoplankton, herbivore do not actually kill the plant species. Only when herbivores kill the plant organism they are preying on is it considered predation, like in seed herbivory. While most herbivores do no kill the plant, they can affect their survival through a loss foliage and roots decreasing overall biomass. It also reduces plant vigor and affects the plants ability to compete through a decrease in reproductive rate. Most plants do not move and are sessile; so certain characteristics have evolved to help them deter herbivores. Some defenses are structural, while others are chemical. Structural defenses include: hairy leaves, thorns, and spines. An example of this is thorns of the acacia tree that can deter herbivores or reduce defoliation by browsers. Some plants contain chemicals that play a role in both metabolic processes and deterring herbivores and reducing the ability of herbivores to digest plant tissue are known as secondary compounds. The three types of compounds are: nitrogen-based compounds, terpenoids, and phenolics. An example of this are lignins that make up nearly 35% of the carbon in terrestrial plant leaves which are complex carbohydrates that herbivores cannot digest. What is a functional response and what is a numerical response? Describe the Type I, II, and III functional responses. Explain what drives each, the assumptions behind each, and provide an example of a situation in which they occur. The definition of a functional response is the relationship between predator consumption and prey density. The definition of a numerical response is the response of the predator population to changing prey density. A type I is like that of the Lotka-Volterra Model. The number of prey captured per unit time by a predator increases linearly with increasing number of prey. The rate of prey mortality due to predation is constant, equal to predation efficiency (c). This response is seen in passive predators such as filter feeders who extract prey from water that washes over their filters. This type of response assumes 1) predators are never full and never stop eating, 2) predators are not limited by handling time. For a Type II functional response , the predator consumption rate rises with prey density, but gradually decelerates until a plateau is reached and the consumption rate remains constant regardless of prey density. This type of response includes the constraint of handling time. As prey