Two models of population growth exponential growth j

  • Queens University
  • BIOL 103
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  • harrystylesislife1995
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Two models of population growth: Exponential growth: (J-shaped curve) Applies in an idealized, unlimited environment Rare in nature except for brief periods in a new environment or seasonally abundant food Logistic growth: (S-shaped curve) Population grows to maximum size of K , the carrying capacity for an environment, set by resource availability (e.g. food, space) Simple, but often models populations reasonably well Life history traits: are those closely linked to Darwinian fitness and evolve in response to biotic and abiotic factors Semelparous reproduction: Common in insects, fish, some plants which use all their energy in a single, immense reproductive effort, e.g. salmon dying after spawning or annual weeds Iteroparous reproduction: Exhibit repeated reproductive cycles throughout their lifetimes, often invest more in each offspring, e.g. many large trees, mammals, birds Population dynamics or demography Need to collect data and create models to estimate vital statistics such as birth and death rates of various types of individuals in a population (males vs. females, old vs young) Information is summarized in a life table and used to compare life histories between species. Most life tables leave out males because males are more or less irrelevant when it comes to producing offspring. Several items are often more important:
Average age individuals start reproducing How often individuals reproduce before dying how many offspring produced at reproduction Pattern of age-related survival (survivorship) Survivorship curves: The most important life history component, shaped by selection acting on the most vulnerable stage of an organisms life cycle. Curves can assume any shape, but it is useful to distinguish 3 common types: 1. Type 1 o Mortality low in juveniles, greatest in old age, usually associated with iteroparity 2. Type 2 Mortality spread evenly across all ages 3. Type 3 Mortality greatest among the young, promoting large reproductive effort; adult survivors may be long lived Exam: might give 5 simple life tables and ask which of the 5 life table represents a population that is growing the fastest? Which is a declining population?
Community Ecology 2016-02-24 Community ecology A biological community consists of interacting species, usually living within a defined area. A community lies between spatial scales of a biome and a population Studies how groups of species interact and form functional communities Species distribute according to “tolerance ranges” due to genetic, physiological, and lifecycle characteristics and interactions with other species. With sharp changes in biotic or abiotic environment, community compositions may change abruptly; areas where distinct communities meet is an ecotone. Often find a broad overlap of species population among environmental gradients; communities grade into each other continuously rather than forming distinct groups, making definition of communities fuzzy.

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