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Transcript
Community Ecology Chapter 54 A community is an interaction between individuals of different species at a place living close enough to have potential interactions. A Habitat is the place where the community lives. 1. Interspecific interactions are between organisms of different species in a community. Examples include Competition, Predation, and Symbiosis. Community interactions are classified by whether they help, harm, or have no effect on the species involved. 2. Interspecific interactions can affect the survival and reproduction of each species, and the effects can be summarized as positive (+), negative (−), or no effect (0). 3. Competition: Interspecific competition (−/− interaction) occurs when species compete for a resource in short supply 4. Competitive Exclusion: Strong competition can lead to competitive exclusion, local elimination of a competing species 5. The competitive exclusion principle states that two species competing for the same limiting resources cannot coexist in the same place 6. Ecological Niches and Natural Selection: The sum of a species’ use of biotic and abiotic resources is called the species’ ecological niche 7. An ecological niche can also be thought of as an organism’s ecological role 8. Ecologically similar species can coexist in a community if there are one or more significant differences in their niches 9. Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community. 10. Character displacement is a tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species. It reduces interspecific competition for similar resources. 11. An example is variation in beak size between populations of two species of Galápagos finches 12. Predation (+/− interaction) refers to an interaction in which one species, the predator, kills and eats the other, the prey 13. Some feeding adaptations of predators are claws, canines, fangs, and poison. 14. Mimicry: In some cases, a prey species may gain significant protection by mimicking the appearance of another species 15. In Batesian mimicry, a palatable or harmless species mimics an unpalatable or harmful model 16. In Müllerian mimicry: Two unpalatable species mimic each other. For example Yellow jacket and Cuckoo bee. 17. Herbivory (+/− interaction) refers to an interaction in which an herbivore eats parts of a plant or alga 18. It has led to evolution of plant mechanical and chemical defenses and adaptations by herbivores 19. Symbiosis is a relationship where two or more species live in direct and intimate contact with one another 20. In parasitism (+/− interaction), one organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process 21. Parasites that live within the body of their host are called endoparasites 22. Parasites that live on the external surface of a host are ectoparasites 23. Mutualistic symbiosis, or mutualism (+/+ interaction), is an interspecific interaction that benefits both species. For example, an alga and a fungus partners in a lichen. 24. In commensalism (+/0 interaction), one species benefits and the other is neither harmed nor helped 25. Facilitation (+/+ or 0/+) is an interaction in which one species has positive effects on another species without direct and intimate contact 26. For example, the black rush makes the soil more hospitable for other plant species 27. Diversity of a community means the species richness and their relative abundance. 28. Species richness is the number of different species in the community 29. Relative abundance is the proportion each species represents of all individuals in the community 30. Diversity and Community Stability: greater the diversity of species the higher is the stability of the community. a. More productive; they produce more biomass (the total mass of all organisms). b. Better able to withstand and recover from environmental stresses c. More resistant to invasive species, organisms that become established outside their native range 31. Trophic structure is the feeding relationships between organisms in a community 32. It is a key factor in community dynamics 33. Food chains link trophic levels from producers to top carnivores Communities have different food chains linked by predation. Each level is called a trophic level. These always start with Autotrophs = producers that use the sunlight to make their food. Top Carnivore = tertiary consumer, lion Carnivore = Secondary consumer, human, cheetah, tiger Herbivore = primary consumer, deer, hare, zebra, antelope Producers = autotrophs, grass, plants 4th trophic level 3rd trophic level 2nd trophic lelvel 1st trophic level 34. Prevalent forms of plants in a community mainly determine the type of animals living in that community. 35. The dead bodies of each level are degraded into simple chemicals by Decomposers = Detrivores 36. Some animals like earthworms, millipedes and many larvae are Detrivores because these feed on dead matter. 37. Bacteria, slime molds and fungi are important decomposers 38. The different organisms like grass or plants, deer or antelope, cheetah or tiger present on same trophic level do not eat each other and are called Competitors. 39. The organisms feeding on different trophic levels like humans are called Omnivores. Humans feed directly on plants and animals. 40. Food Chain is linear and joined by predation. Grass Deer Lion 41. Omnivore feeds at more than one trophic levels – bears, humans 42. Detrivores feed on detritus, a partially decomposed plant or animal part. 43. Food Web has many interconnected food chains. Only food webs exist in nature 44. A food web is a branching food chain with complex trophic interactions 45. Species may play a role at more than one trophic level 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. Each food chain in a food web is usually only a few links long (mostly not more than 6). Dominant species are those that are most abundant or have the highest biomass Keystone species exert strong control on a community by their ecological roles, or niches In contrast to dominant species, they are not necessarily abundant in a community Field studies of sea stars illustrate their role as a keystone species in intertidal communities Sea otters feed on sea urchins and prevent them from overcrowding and keep kelp forests stable. Ecosystem engineers (or “foundation species”) cause physical changes in the environment that affect community structure For example, beaver dams can transform landscapes on a very large scale A disturbance is an event that changes a community, removes organisms from it, and alters resource availability. Disturbance of Communities, when moderate in severity and occurrence leads to increase in diversity of species in the community. Disturbance usually leads to Ecological Succession. Ecological Succession is Primary when it starts on bare wood, sand or rock with no soil. For example, rocks exposed by receding glaciers in Alaska. It takes hundreds of years to reach climax community. Disturbances like hurricanes, fires eliminate the community but leave the soil intact – The Succession is called Secondary, it takes lesser time to reach climax community. For example, abandoned agricultural land may return to its original state through secondary succession Human Disturbance: Humans have the greatest impact on biological communities worldwide Both terrestrial and marine ecosystems are subject to human disturbance Human disturbance to communities usually reduces species diversity Latitudinal Gradients: Species diversity in a community falls along an equatorial (0˚) to polar (90˚) gradient. Two key factors in equatorial-polar gradients of species richness are probably evolutionary history and climate Temperate and polar communities had to start time and again after glaciations (ice age) and tropical communities have been stable for long periods. Growing season is limited in temperate or polar communities but tropical communities have longer growing season. Climate is likely the primary cause of the latitudinal gradient in biodiversity Two main climatic factors correlated with biodiversity are sunlight and precipitation Can be studies together by measuring a community’s evapotranspiration. Evapotranspiration is evaporation of water from soil plus transpiration of water from plants Pathogens, disease causing organisms, alter community structure locally and globally. Pathogens can have dramatic effects on communities For example, coral reef communities are being decimated by white-band disease