ENV100Y5 Lecture Notes - Lecture 17: Character Displacement, Ecological Niche, Background Extinction Rate
Module 2: May 22-June 1
Date: Sunday, May 27
SESSION 18: SPECIES INTERACTIONS AND COMMUNITY ECOLOGY (I)
Readings: Chapter 5
What Limits Population Growth?
● Density-dependent factors = limiting factors whose influence is affected by population
density (e.g. disease, parasites, competition - run out of resources quickly...); depend on
population size - larger population, easier to transmit parasites and catch a disease,
population cycles; limited by growth of population itself
● Density-independent factors: limiting factors unrelated to population density (e.g., natural
disasters, weather, climate change), ex. decline in Galapagos finch population due to
severe drought
Population Growth is like a cruise ship - hard to change course, takes a while
● Population growth is like cancer - absolute rate is high, early on it starts to divide,
doubling rate is two weeks, the per capita rate is the same, but absolute rate picks up
because individuals give rise to more cancer
Doubling time ~70/(growth %) - the time it will take the population to double
● E.g. if a population at 7%/year, it will take ~70%/7 or approximately 10 years to double
● Current growth rate: 1.1%/yr; at this rate global human population will double in 64 years
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Interactions with Environment: Habitat
● The environment in which an organism lives and functions
● Living and nonliving components
● Scale depends on organisms
Ecological Niche
● An organism's use of resources and its functional role in community
● Fundamental niche: optimal conditions
● Realized niche: a subset of fundamental niche due to species interactions
Habitat Specialists & Habitat Generalists
● Specialists = narrow niches and very specific requirements, ex. golden toad lives in
specific temp. water
● Generalists = broad niches that can use a wide array of habitats and resources, ex. frog
lives anywhere
● The specialists are more likely to go extinct, and generalists are more likely to survive
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ENV100Y5 Full Course Notes
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Document Summary
Session 18: species interactions and community ecology (i) Density-independent factors: limiting factors unrelated to population density (e. g. , natural disasters, weather, climate change), ex. decline in galapagos finch population due to severe drought. Population growth is like a cruise ship - hard to change course, takes a while. Doubling time ~70/(growth %) - the time it will take the population to double. E. g. if a population at 7%/year, it will take ~70%/7 or approximately 10 years to double. Current growth rate: 1. 1%/yr; at this rate global human population will double in 64 years. The environment in which an organism lives and functions. An organism"s use of resources and its functional role in community. Realized niche: a subset of fundamental niche due to species interactions. Specialists = narrow niches and very specific requirements, ex. golden toad lives in specific temp. water. Generalists = broad niches that can use a wide array of habitats and resources, ex. frog lives anywhere.
