es_100_lecture_19

es_100_lecture_19 - Announcements Midterm 2 Monday NO make...

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Unformatted text preview: Announcements: Midterm 2, Monday. NO make ups. Review session: Bren Hall 4L, ES seminar room, center of hall. 10:30 – 11:30. Bring questions. Regrades for exam 1 due today in class. MUST BE WRITTEN REQUESTS WITH JUSTIFICATION. NO section this week. Lecture 19 Intermediate disturbance - terrestrial systems Disturbance, productivity and diversity Community theory Intermediate disturbance hypothesis does not work as well in terrestrial ecosystems 1. Disturbance regimes harder to quantify and harder to manipulate Fewer experiments have been done creating different dist. regimes and directly testing the hypothesis 1. Terrestrial systems more open to immigration and emigration of species. More opportunity for chance colonization events. 2. Wider range of life histories among the plants. Includes variation in seed dormancy, resistance to disturbance, mechanisms of response to disturb . Example of a controlled experiment with grazers as disturbance agents. Maybe intermediate grazing intensity has highest richness ??? Figure 7.24 Townsend low high Selective predation reduces competitive dominant increases diversity Disturbance = hard to control and quantify The two sites behaved rather differently. Intermediate disturbance hypothesis does not work well in terrestrial ecosystems 1. Disturbance regimes harder to quantify and harder to manipulate 2. Systems more open to immigration and emigration of species 3. Wider range of life histories among the plants 4. Site productivity can play a strong role in controlling response to disturbance Lecture 11: Grazing experiment at Sedgwick reserve. Cows had a strong effect only in some sites…… In richer soil native species richness is enhanced by grazing. ( Richer soil , spring 2008) Small plots (0.5 m 2 ) ungrazed grazed Number of species 1 2 3 4 5 6 7 ungrazed grazed 5 10 15 20 25 Large plots (500 m 2 ) Number of species ** *** In low productivity sites there is no clear competitive dominant and no effect of grazing. ....
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es_100_lecture_19 - Announcements Midterm 2 Monday NO make...

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