Lecture 5 Ricklefs Notes

Chapter 19 (all), Chapter 23 (486-493), and Chapter 24 (515-516)
-Communities exist in a state of constant flux, with energy and nutrients passing through the community.
-Communities rebuild after they are disturbed. Succession is the sequence of changes initiated by disturbance. Climax community is the ultimate association of species achieved.
-The creation of any new habitat attracts a host of species that are adapted to be good pioneers.
-The character of the community changes over time. Within a given biome, similar climax communities may e reached after several successional sequences (seres). The initial stages of the sere depend on the habitat where it begins. Two types of seres: Primary Succession - establishment and development of communities in newly formed or disturbed habitats devoid of life. Secondary Succession - regeneration of a community following a disturbance
-Climax Community - traditionally viewed as the ultimate expression of community development in succession, but now the concept of the climax as a closed system has been rejected by many ecologists. Now, use a continuum index, which is the scale of an environmental gradient based on changes in physical characteristics or community composition along that gradient.
-Succession occurs as colonists are able to alter the environmental conditions of a habitat Can be facilitation, where one species increases the probability of a second species becoming established. Also can be inhibition, where the presence of one species inhibits the colonization of another species. Inhibition can create a priority effect, where the outcome of an interaction between two species depends on which becomes established first. Tolerant species, however, are not influenced by their interactions with other species, but on their dispersal ability and their tolerance of the environment's physical conditions.
-The place in a sere determines the characteristics of species. Early successional, or pioneer, species have small, easily-dispersed seeds and produced offspring that are shade-intolerant and reach maturity quickly. That is why they are good colonizers. Late successional species have the opposite characteristics, which makes them good competitors.
-Succession is thought to occur until new species stop being added and species exclusion no longer change the community environment.

-The global hydrologic cycle illustrates many basic features of the cycles of elements, such as energy requirements and releases. Precipitation and evaporation are essentially equal in the cycle.
-Three classes of processes cause carbon to cycle through ecosystems: assimilatory and dissimilatory reactions (photosynthesis and respiration), exchanges of CO2 between the atmosphere and the oceans, and precipitation of carbonate sediments in the oceans.
-CO2 is continuously exchanged between the atmosphere and surface waters through bicarbonate and carbonate ions.

-It is uncertain how much thawing of frozen soils at high latitudes will accelerate global warming is uncertain at this point.

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