are the species in the community p is the relative abundance of each species

Are the species in the community p is the relative

This preview shows page 14 - 17 out of 20 pages.

are the species in the community, p is the relative abundance of each species, and ln is the natural logarithm b. Trophic Structure: the feeding relationships between organisms i. Food chain : transfer of food energy up from its source in plants and other autotrophic organisms (primary producers) through herbivores (primary consumers) to carnivores (secondary, tertiary, and quaternary consumers) to decomposers 1. Food webs: food chains are linked together (arrows linking species according to who eats whom) a. A given species may weave into the web at more than one trophic level b. Nonexclusive consumers are also found in
Image of page 14
terrestrial communities 2. Limits on Food Chain Length a. Energetic hypothesis : the length of a food chain is limited by the inefficiency of energy transfer along the change b. Biomass : the total mass of all individuals in a population c. Dynamic stability hypothesis : long food chains are less stable than short chains d. Carnivores in a food chain tend to be larger at successive trophic levels c. Species with a Large Impact i. Dominant Species 1. Dominant species: species in a community that are the most abundant or that collectively have the highest biomass (competitively superior in exploiting limited resources, most successful at avoiding predation or the impact of disease?) 2. Invasive species : organisms that take hold outside their native range ii. Keystone Species : not necessarily abundant in a community 1. Exert strong control on community structure not by numerical might but by their pivotal ecological roles iii. Foundation Species (Ecosystem “Engineers”) 1. Species that dramatically alter their physical environment on a large scale 2. Facilitators : species that have positive effects on the survival and reproduction of other species in the community d. Bottom-Up and Top-Down Controls i. V H: increase in vegetation with increase biomass of herbivores ii. V H: increase in herbivore biomass with decrease the abundance of vegetation iii. V  H iv. Bottom-up model : unidirectional influence from lower to high trophic levels (N V H P) v. Top - down model : predation mainly controls community organization because the predators limit herbivores, herbivores limit plants, and plants limit nutrient levels through their uptake of nutrients during growth and reproduction (trophic cascade model, alternation +/- effects) vi. Wall and Virginia: top-down model (Antartica) vii. Biomanipulation : applying top-down model to alter ecosystem characteristics 3. 54.3 Disturbance influences species diversity and composition a. Stability: a community’s tendency to reach and maintain a relatively
Image of page 15
constant composition of species b. Climax community: community of plants at a site have only one state of equilibrium, controlled solely by climate c. Disturbance : an event that changes a community by removing organisms from it or altering resource availability d. Nonequilibrium model : describes most communities as constantly changing after being affected by disturbances i. Characterizing Disturbance 1. Intermediate disturbance hypothesis : moderate levels of disturbance can create conditions that foster greater species
Image of page 16
Image of page 17

You've reached the end of your free preview.

Want to read all 20 pages?

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes