Go Over Quiz Symbiosis Succession Ecosystem Structure and Regulation

Transcription

1 Goals Go Over Quiz Ecosystem Structure and Regulation Natural Selection Review 1. Organisms beget like organisms. 2. There are chance variations between individuals in a species. Some variations are heritable. 3. More offspring are produced each generation than can be supported by the environment. 4. Some individuals, because of their physical or behavioral traits, have a higher chance of surviving and reproducing than other individuals in the same population. Dynamic Equilibrium Model Community Structure community structure is maintained by controlling competitive interactions between species (e.g., keystone species) Page 423 in Text Community Structure A keystone predator is an animal that is important for maintaining species richness (number of species) in a community. Keystone predators feed on different species that normally would compete with each other. Competitive exclusion of a species does not occur because the densities of competitors are kept reduced by a common predator. A good example of a keystone predator is Piaster, a sea star, that reduces the populations of a mussel, Mytilus. If Piaster is experimentally removed from the community, the species richness of the community decreased from 15 to 8 species. 1

2 Review Conserving Diversity Tend to focus on species even only rare species Current efforts starting to shift to conserving complete ecosystems There are an estimated 1030 million species described in the world; only 1.7 million described! Extinction rates are increasing natural rate 225 spp. / yr present rate 10,000 spp. / yr. intimate association between individuals of two different species living together Types of Trophic exchange of nutrients and energy Dispersive food in return for moving propagules or pollen Defensive food or shelter in return for defense 2

3 Soybean & Rhizobium Facultative partners can live singly Obligate partners cannot exist singly Lichen fungus and cyanobacteria or green algae Lichen on a Tree 3

4 Cocklebur & Animals Ants and Acacia Remora and Shark Sawfly (Pontania sp.) larva inside a gall. Note the external parasitoid larva (translucent white) attached to the dorsal surface of the sawfly larva. d.net/vol/v3/experiments/sawfly/img/sawfly(parasite)%25 5BHR%255D.jpg&imgrefurl= experiments/sawfly/downloads.html&h=1061&w=721&sz =107&tbnid=IwoeejTl0bMJ:&tbnh=150&tbnw=101&hl=e n&start=9&prev=/images%3fq%3dparasite%26svnum %3D10%26hl%3Den%26lr%3D 4

5 the (orderly or predictable or directional) replacement of species in a habitat following a disturbance or creation of new substrate; generally leads to a stable community Late succession Climax trees It is Nonseasonal Early successional trees shrubs Primary succession following the retreat of a glacier Annual weeds Herbaceous perennials time Seral Stages Primary succession on newly formed substrate (e.g., sand, rock, lava flows; involves substantial modification by colonists Secondary succession after moderate disturbances that leave much of the physical structure of the ecosystem intact. As vegetation changes so do animals 5

6 Three Mechanisms of Connell and Slatyer (1977) Three Mechanisms of 1. Facilitation each seral stage changes environment to favor next step often via soil improvement (addition of litter, N fixing species 2. Inhibition one species prevents establishement of another (predation/ herbivory, competion, chemical inhibition, aggressive behavior). al pattern may be determined by which species arrives first. Life history important/ long lived species favored A B A B C D C D Three Mechanisms of 3. Tolerance depends on relative ability of a species to tolerate physical conditions Sere is determined by competitive exclusion Facilitation, Inhibition and Tolerance are working in most seres Pioneer species may facilitate next stage by preparing soil or substrate Better competitors will replace pioneer species (inhibition) Some stages may experience stressful environmental conditions (tolerance) Other factors predation, herbivory, disease?? A B C D 6