Lecture Note 15 Community Ecology

12/3/20 Lecture 15 Community Ecology Community Ecology • Ecological community: a group of interacting species living in the same location • Focuses of community ecology: 1. Biodiversity 2. Interspecific interactions 3. Community structure 1 12/3/20 1. Biodiversity • Biodiversity: deg...

12/3/20 Lecture 15 Community Ecology Community Ecology • Ecological community: a group of interacting species living in the same location • Focuses of community ecology: 1. Biodiversity 2. Interspecific interactions 3. Community structure 1 12/3/20 1. Biodiversity • Biodiversity: degree of variation of life forms within a given area - Affected in part by climate At species, ecosystem and genetic levels • Extinction: complete loss of a species - Mass extinction: a sharp decrease in the diversity Uneven Distribution of Biodiversity Biodiversity depends on: - Temperature - Precipitation - Altitude - Soil - Geography - Presence of other species Richer in tropical than in polar regions; Richer in terrestrial than in ocean areas. 2 12/3/20 Rainforests: most productive and most complex ecosystems on Earth video Five mass extinctions have occurred in the history of life on earth – “Big Five” Number of marine families Mass extinctions Are we now experiencing the beginning of biodiversity’s sixth mass extinction? Millions of years ago In mass extinctions, over 50% of animal species died; Over 99% of documented species are now extinct. Figure 14.2 3 12/3/20 The worst Most famous The Primary Causes of Extinction Habitat: an ecological area that is inhabited by a particular species Figure 14.5 4 12/3/20 2. Interspecific Interactions • Species interact in various ways: - Competition: species compete with each other for finite resources (food, light, etc.) - Negative-negative interaction - Predation (Herbivory and Parasitism): species survives by eating other species - Positive-negative interaction - Mutualism: a symbiotic interaction between species in which both benefit - Positive-positive interaction Mutualism Mycorrhiza (fungi) Living with plant roots Bees as pollinators for flowers Figure 14.13, 14.14 5 12/3/20 3. Community Structure • Food Web: the feeding connections in an ecological community • Two trophic levels - Autotrophic: produce organic matter from inorganic substances (minerals, gases) à Producer - plants, cyanobacteria (blue-green algae), phytoplankton - Heterotrophic: must feed to obtain organic matter à Consumer - herbivores, carnivores, decomposers (bacteria, fungi, worms) Other birds Smaller-toothed whales Other seals Sperm whales Leopard seal Baleen whale Carnivorous zooplankton Penguins Fish Krill Elephant sea; Other Squid herbivorous zooplankton Phytoplankton Figure 14.12 6 12/3/20 The movement of mineral nutrients is cyclic, whereas the movement of energy is unidirectional and noncyclic 7 12/3/20 Only 10% energy passes to the next trophic level 10 Cal 100 Cal 1,000 Cal 10,000 Cal 100,000 Cal of sunlight energy 8 12/3/20 3. Community Structure • Ecological succession: the structure of the community evolves over time - Primary succession: the colonization of habitats devoid of life - Secondary succession: the reestablishment of a community that does not eliminate all life Primary succession: Volcanic rock in Table Mountain, CA (a); The transition from pond to land in Vasco Caves, CA (b). Secondary succession: Prescribe fires (b) burned Lodge pole pines (a) trees in the meadow (c). 9 12/3/20 Species with a large impact on community structure • Dominant species: the most abundant species in a community • Keystone species: the key species in determining the food web of an ecosystem • Ecosystem engineer: the species that creates or modifies habitats • Facilitator species: the species that benefits the habitats Keystone: a crucial block in an arch that keeps it from collapsing The loss of the keystone species results in a drastic shift among the species in a food web Carnivorous starfish in the intertidal ecosystem 10 12/3/20 Figure 1: Food web of species present in temperate intertidal ecosystem Figure 2: Effect of removal of top predator on total species number in intertidal ecosystem Beaver: keystone species, ecosystem engineer, facilitator species Coral (A), oyster (B) and mangrove (E): marine ecosystem engineers 11 12/3/20 Saving Species – Protecting Habitat video • Biodiversity hotspots: 2% of the earth’s surface contain 50% of the earth’s animal and plant species California Floristic Province Mediterranean Basin Caribbean Caucasus Philippines South Central IndiaChina Burma Polynesia/ Mesoamerica Brazil’s Micronesia Cerrado Choco/ Tropical Western W. African Tanzania Polynesia/ Andes Ghats and Darien Forests and Micronesia Sri Lanka Wallacea Western Kenya Sundaland Ecuador New Brazil’s Succulent Central Madagascar Caledonia Atlantic Karoo Southwest Chile Cape Floristic Coast Diversity hot spots Australia New Zealand Province Figure 14.21 Saving Species – Conservation Genetics Low genetic variability leads to low fitness • Heterozygotes can avoid effects of recessive alleles • Homozygote 1: Relatively low fitness (only one type of jacket in wardrobe) Figure 14.23 Homozygote 2: Relatively low fitness (only one type of jacket in wardrobe) Heterozygote: Relatively high fitness (two types of jackets in wardrobe) 12 12/3/20 Consequences of low genetic variability: a small population can become stuck in a cycle that leads to extinction Small population Inbreeding Genetic drift Loss of genetic variability Reduction in fitness and population adaptability High mortality Low reproduction Figure 14.26 Small population 13