Text of Recap: Ecological Succession Succession concepts, type of succession Mechanisms of succession Climax...
Recap: Ecological Succession Succession concepts, type of succession Mechanisms of succession Climax community
16.3 Succession becomes self-limiting as it approaches the climax Succession continues until the addition of new species to the sere and the exclusion of established species no longer change the environment of the developing community. The progression from small to large growth form modifies the conditions of light, temperature, moisture and soil nutrients. Conditions change slowly after the vegetations achieves the largest growth form that the environment can support. Final dimensions of a climax community are limited by climate independently of events during succession.
Succession becomes self-limiting as it approaches the climax Time required for succession from a new or disturbed habitat to a climax community depends on nature of climax and initial quality of habitat Mature oak-hickory climax forest from old field in North Carolina: 150 yrs Climax stage of grasslands in western North America: 20-40 years Humid tropics, reach climax within 100 years from clear cut, but may take a few more centuries to achieves a fully mature structure and species composition. Sand dune beech-maple climax, up to 1,000 years Climax is an elusive concept: Communities also change in response to climate change, hunting, fire, and logging, disappearance of keystone consumers (wolf, passenger pigeon) and trees (chestnuts, eastern hemlock)
Climax communities under extreme environmental conditions Fire is an important feature of many climax communities, favoring fire-resistant species and excluding species that would otherwise dominate. Longleaf pine after a fire Seedling may be badly burned, but the growing shoot is protected by the long, dense needles.
Grazing pressure also modify a climax community Grassland can be turned into shrubland by intense grazing Herbivivores may kill or severely damage perennial grasses and allow shrubs and cacti that are unsuitable for forage to invade. Selective grazing Some species prefer to feed on areas previously grazed by others. Both zebras and Thompsons gazelles feed on Serengeti ecosystem of east Africa, but eating different plants. In North America, cattle grazing may lead to invasion by alien cheatgrass, which promote fire.
Transient and cyclic climaxes Succession is a series of changes leading to a stable climax, whose character is determined by local environment. Once established, a beech-maple forest perpetuates itself, and its general appearance changes little despite constant replacement of individuals within the community. Transient climaxes: such as communities in seasonal ponds small bodies of water that either dry up in summer, or freeze solid in winter. The extreme seasonal changes regularly destroy the communities that become established in the ponds each year. On African savannas, carcasses of large mammals are devoured by a succession of vultures including: large, aggressive species smaller species that glen smaller bits of meat from bone species that cracks open bone to feed on marrow.
Cyclic climax: Suppose, for example, species A can only germinate under species B, B only under C, and C only under A. The relationships create a regular cycle of species dominance in the order of A, C, B, A, C, B, A, , in which the length of each stage is determined by the life span of the dominant species. Cyclic succession is usually driven by stressful environmental conditions.
When high winds damage heaths and other types of vegetation in northern Scotland, shredded foliage and broken twigs create openings for further damage, and soon a wide swath is opened in the vegetation. Regeneration occurs on the protected side of damaged area while wind damage further encroaches on exposed vegetation. Temporal: wind damage and regenerate, cycling Spatial: mosaic patches
BIOL 4120: Principles of Ecology Lecture 17: Biodiversity Dafeng Hui Office: Harned Hall 320 Phone: 963-5777 Email: email@example.com
Species richness varies over the surface of the earth Why so may species in tropics and few toward the poles? 1 hectare of forest Boreal: