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Ecology Lec 8 (life history) summary.docx

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Western University
Biology 2483A
Hugh Henry

Ecology Lec 8- Life History Life history- record of events of growth, development, reproduction, survival Nemo case study- clownfish non-breeders, breeding male, largest is dominant female - hatchlings move out, find new anemone - 2 similar size, fight, one leaves (dies) - favorable to not grow to conflicting size Life history strategy- a species’ overall pattern of timing of life history events - best timing = optimal distribution of growth, repro, survival - Natural selection favors best timing (no strategy is perfect- tradeoffs etc) Phenotypic plasticity- One genotype produces different phenotypes in different conditions - results in continuous range of sizes, or discrete types called Morphs Polyphenism- single genotype produces several distinct morphs - E.g. spadefoot tadpoles have 2 morphs Omnivores- grow slowly, favored in ponds that last long Carnivores- grow fast, die fast, favored in ponds that dry up quickly Allometry- change morphology by diff body parts grow at diff rates = changes shape/proportion Modes of Reproduction Asexual- binary fission (proks & protists) Some multicellular- Both sexual & asexual (e.g. corals) Sexual- Benefit: recombination- genetic variation, better able to respond to enviro changes Disadvantage: only ½ of genome passed on, slow pop’n growth Isogamy- both gametes equal in size Anisogamy- gametes diff sizes. Usually egg is larger & contains nutrients. Most multicell. Orgs Direct development- fertilized egg → juvenile without larval stage Complex life cycles- 2 stages larval & juvenile (with abrupt transition- called metamorphosis) - both stages very different body form & habitat - Semelparous- reproduce only once (e.g. annual plants, agave) - Iteroparous- reproduce multiple times (e.g. pine tree, spruce tree, most mammals) Life history continua- reproductive pattern/strategy continuum - r-selection vs K-selection- are two extremes r-selected- r is the intrinsic rate of increase of a population - r-selection: for high pop’n growth rates, newly disturbed habitat, uncrowded - short life, fast development, early maturation, high repro rates, low parent investmnt - insects, small animals K-selected- K is the carrying capacity for a pop. - K-selection: for slower growth rates, pop near K, crowded, efficient repro favored - long lived, slow development, late maturation, low repro rates, high parent investmt - large mammals, reptiles, long lived plants Classification scheme for plant life history Stress- any abiotic factor that limits growth Disturbance- any process that destroys plant biomass 4 habitats possi
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