ENVS 1126 Chapter : Chapter 4 Populations And Communities
Chapter 4 Populations and
Communities 1/23/17
• Population
Population growth curves chart (important) carrying capacity
Environmental resistance – The biotic and abiotic factors that limit a
population’s increase
Biotic potential – number of offspring produced under ideal conditions
R-strategist – produce as many offspring as possible
K-strategist – 1-3 offspring (energy high in parental care) Ex: Lion
R-selected species – adapted to a rapidly changing environment
K-selected species – well-adapted to normal environmental
Population density – density-dependent factor (food) and density-
independent factor (cold weather)
o Density-dependent factor: effects depend on population density.
Will increase with increased population density
Ex: Disease, predation, food shortage
o Density-independent factor: effects are independent of population
density
Ex: Fire, spring freeze
• Community
-Mutualism (++) – Two organisms need each other Ex: Bee and flower
-Predation (Predator vs. prey) /Parasitism (Parasite vs. host) (+-)
-Keystone species - Ex: Beaver – when build dam. Ecosystem would collapse
without them
Top-down regulation – Control of a population by predator
Bottom-up regulation – Control of a population by resource
-Competition (--)
o Intraspecific competition – Territory. An area defended by an
individual or group. Same species (--)
o Interspecific - Competitive exclusion principle – 2 species that
compete for same resources cannot stably coexist. Different species
(+-)
• Resource partitioning – Division of a resource and specialization in
different parts of it
Ex: Lizards in tree
• Evolution
Selective pressure – environmental resistance factors that affect survival
and reproduction
Ex: Predators, paradise, droughts
Document Summary
Environmental resistance the biotic and abiotic factors that limit a population"s increase. Biotic potential number of offspring produced under ideal conditions. R-strategist produce as many offspring as possible. K-strategist 1-3 offspring (energy high in parental care) ex: lion. R-selected species adapted to a rapidly changing environment. Population density density-dependent factor (food) and density: density-dependent factor: effects depend on population density. independent factor (cold weather) Ex: disease, predation, food shortage: density-independent factor: effects are independent of population density. Predation (predator vs. prey) /parasitism (parasite vs. host) (+-) Mutualism (++) two organisms need each other ex: bee and flower. Keystone species - ex: beaver when build dam. Top-down regulation control of a population by predator. Bottom-up regulation control of a population by resource: intraspecific competition territory. An area defended by an: interspecific - competitive exclusion principle 2 species that, resource partitioning division of a resource and specialization in.
