Community Ecology Populations of different species living in the same place NICHE The sum of all the different use of abiotic resources in the habitat by s given species what the organism does what is done to the organism biotic (living) and abiotic (nonliving) factors salts birds decaying leaves moisture soil composition HABITAT: the kind of place occupied by the organisms e.g. a grassland, a forest, a coral reef moles ph Organisms Interactions 1) Beneficial / Harmful = (+/-) PREDATION: One animal is food for the other. The one that is food is killed Between two different organisms cheetah chameleon predators preys PARASITISM: One animal is food for the other! The one that is food is alive while serving as food Lamprey (parasite) tapeworm Fish (host) The host is in general weakened and more susceptible to predation or diseases 1
2) Beneficial / Not affected = (+/-) COMMENSALISM: e.g. epiphytes, plants that use trees as support to reach the sunlight e.g. remora living attached to sharks 3) Beneficial / Beneficial = (+/+) MUTUALISM: Bacteria that eat cellulose in the guts of herbivores butterflies eating nectar from flowers and transporting pollen from one flower to another Lichen (algae/fungi) Mycorrhizae (fungi/plants) 4) Harmful / Harmful = (-/-) COMPETITION Interspecific: between individuals of different species Both individuals are harmed to some extent Occurs when both organisms need a vital resource that is in short supply More similar the requirements more intense the competition is Intraspecific: Among individuals of the same species vultures Competitive exclusion principle (States that if two species have an ecological niche that is too similar, the two species cannot coexist in the same place) Extinction Migration (of the less competitive species) Adaptation to a different resource Resource partitioning Number of individuals Sp 1 Niche variable (e.g.food) Sp 2 Sp 1 Sp 2 2
Organisms Adaptations Cryptic coloration is camouflage, a way for prey to hide from predators A warning coloration is a brightly colored pattern Warns predators that an animal has an effective chemical defense Mimicry is a form of defense in which one animal looks like another species. Ecosystem Ecology Ecosystem ecology: Deals with energy flow in the system, A community s trophic structure (feeding relationships) determines the passage of energy and nutrients from plants and other photosynthetic organisms to herbivores, and then to predators species populations communities ecosystem Environment: anything that surrounds and affects an organism during its lifetime (Biotic and abiotic factors) Living: Other organisms Nonliving: Temperature Water Rainfall Sunlight 3
Food chain: Linear representation or sequence of organisms feeding on one another 4 th consumers = carnivores 3 rd consumers = carnivores Trophic level: each stage or step in the food chain Omnivores organisms like humans do not fit in a linear representation of a food chain eat both animals and plants 2 nd consumers = carnivores 1 st consumers = herbivores producers = autotrophs (photosynthetic organisms: plants, algae, cyanobacteria) Neither do Decomposers organisms like fungi and bacteria eventually return nutrients to the soil Food webs Are a more realistic representation of the trophic interactions in a community Several food chains at each community The same organisms can be part of several food chains Keystone species is a species whose impact on its community is much larger than its total mass or abundance indicates Top predators are normally keystone species! 4
Keystone predators Directly or indirectly regulate the number of other organisms & the diversity of the ecosystem Without predation Only the best competitors survive at each place Diversity is severely reduced Excessive number of predators Reduce diversity as well Energy flow in ecosystems Why the pyramid structure? (1) The broad energetic base (producers) is necessary to support the upper levels (2) Energy is lost from one level to another as heat: 10% gets passed on average! Metabolic activities, capture and processing of food, etc, energy is used and lost as heat Biomass organization in ecosystems (dry weight of a given trophic level) Same principle applies! More people can be fed as herbivores than carnivores! 5
Disturbances are episodes that damage biological communities by Destroying organisms Altering the availability of resources such as mineral nutrients and water. Ecological Succession Disturbances may cause a gradual replacement by other species Climax: stable and long lasting communities Primary succession: Begins in a virtually lifeless area with no soil A soil layer needs to be generated Secondary succession: community is disturbed by natural or human action, and a new successional process begins Layer soil is already present Reservoir of seeds may exist 6
Cycling of materials in ecosystems C, H 2 O, N, P 1) Carbon Cycle Only sunlight energy comes to the Earth on a continuous basis This energy drives all the biological processes The Earth is considered a closed ecosystem Carbon Raw material for photosynthesis Main component of all organic molecules 2) The Hydrologic Cycle: cycling of water is a result of physical processes Reservoir capacity (n*1000 km 3 ) Water: 75% of the Earth Freshwater: 4% Saltwater: 96% The global water balance ATMOSPHERE d Retention time (d=days, y=years) Volume transported between reservoirs (n*1000 km 3 ) 1.8% LAKES - RIVERS y GROUNDWATER y CONTINENTS <0.2% 96% OCEANS y POLAR CAPS y 2% 7
3) Nitrogen Cycle Nitrogen Raw material for Proteins, nitrogenous bases, ATP Only a few bacteria can convert N2 to compounds that are usable for plants N limits the plant biomass in terrestrial environments 4) Phosphorus Cycle Phosphorous The phosphorus cycle does not have an atmospheric component. Raw material for nucleic acids, ATP, and other organic molecules P limits the biomass in aquatic environments 8