factors that regulate natural populations chapter 11.3 mcgraw-hill ryerson (2011)
DESCRIPTION
Density-dependent factors 1.Intraspecific competition is when individuals of the same species compete for resources. If this is high then the population will have a low growth rate.TRANSCRIPT
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Factors that regulate Natural populations
Chapter 11.3McGraw-Hill Ryerson
(2011)
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Factors Affecting Population Change
A. Density-dependent factors limit population growth and intensify as the population increases in size (i.e. Competition for resources, disease...)
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Density-dependent factors
1. Intraspecific competition is when individuals of the same species compete for resources. If this is high then the population will have a low growth rate.
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Density-dependent factors
2. Predation is the consumption of prey by a predator. If there is more prey available they will be chosen more by predators.
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Density-dependent factors
3. Allee effect: Warder Allee found that some density-dependent factors reduce population growth when the population is at a low density rather than high density.
– Ex. harder for individuals to find a mate and successfully reproduce thus lowering the growth rate of species.
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Allee-effect continued
• Small populations also may go through inbreeding depression which reduces the populations' genetic variability and may prevent successful population growth.
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Allee-effect continued
• The minimum viable population size is the smallest number of individuals that ensures the population will persist for a certain period of time.
• Allows biologists to determine whether a species is endangered.
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Factors Affecting Population Change
B. Density-independent factors limit population growth no matter what the population size
i.e. Natural disaster, human intervention...
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Density-independent factors
• The resource in the ecosystem that is in the shortest supply is known as the limiting factor since it is preventing massive population growth.
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Population Change Affects the Entire Ecosystem
• A change in one population of species can affect the entire hierarchy of living things in that ecosystem. Ex. The disappearance of
beaver from this ecosystem causes a decrease in the wolf population which would cause an increase in its other prey
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INTERACTIONS WITHIN COMMUNITIES
• Community: Populations of different species living in the same area.
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INTERACTIONS WITHIN COMMUNITIES
• Ecological niche: The role an organism fills within a community (what it does, eats, its pattern of living)
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INTERACTIONS WITHIN COMMUNITIES
• Interspecific competition: competition for resources among members of two or more different species.
Hyenas battle with a lioness and win the day. Photo by Brittany Gunther, 2008
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Types of Niches:
• Fundamental niche: the role the organism would fill under ideal enviromental conditions (if there was no interspecific competition).
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• Realized niche: the portion of the fundamental niche the organism actually fills (due to competition).
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A. Symbiosis• Interactions in which members of two (or
more) species maintain a close association. • There are 3 main types:
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1. Parasitism• The interaction is
beneficial to one species and harmful (but not fatal) to the other species.
• Parasites can be both micro- and macroscopic as well as ecto- and endoparasites.
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• Social parasites mimic the behaviour of another species in order to complete their lifecycle (i.e. cowbirds).
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2. Mutualism• The interaction is beneficial to
both species. Ex. Bees and flowers
• Obligatory mutualism is when neither species can survive without the other (gut bacteria in herbivores, oxpecker birds).
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3. Commensalism
• The interaction is beneficial to one species while the other is unaffected.
• Remoras and sharks are a possible example.
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B. Types of Interspecific Competition:
1. Interference Competition: two species are actually fighting over the resources (birds over birdhouses, lion vs. hyena).
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B. Types of Interspecific Competition:
2. Exploitative Competition: two species are using a common resource and one species is more efficient at obtaining it ex. arctic foxes and snowy owls eating arctic hares, canopy trees in rainforest.
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Gause's Principle/ Principle of Competitive Exclusion:
• if the resources are limited, no two species can remain in competition for exactly the same niche indefinitely.
• One species will always out compete the other.
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Resource Partitioning• The avoidance of, or
reduction in, competition for similar resources by individuals of different species that do not occupy the same niche
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Resource Partitioning• i.e. Plant root systems, lizards/insects/birds in
different parts of the tree.
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C. Predation• Predator-prey relationships are
an important interaction in a community.
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C. Predation• When the prey population increases, the predator
population will increase shortly thereafter. Predator-prey populations follow a cyclical pattern.
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C. Predation
• Predator-prey interactions have caused prey to evolve diverse defence mechanisms in order not to be eaten.
• Predators are evolving to bypass these defences (Evolutionary Arms Race).
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D. Defense Mechanisms• Plants use morphological defenses such as
thorns, hooks, needles, spines and chemical defenses such as toxins, hormones, and other chemicals to deter herbivores from eating them.
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D. Defense Mechanisms
• Animals use passive defences such as hiding / being poisonous or active defences such as fleeing/ fighting/ producing venom.
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D. Defense Mechanisms
• Some animals use mimicry, which is one species appearing very similar to another species.
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D. Defense Mechanisms
• Batesian mimicry: a harmless species mimics a harmful one (ie. An edible butterfly mimics a toxic species so it won't get eaten)
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D. Defense Mechanisms
• Mullerian mimicry: dangerous species all appear similar which causes predators to learn quickly to avoid them.
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Homework
• Pg 519 #1, 3, 5, 6, 7, 9, 10, 11, 14, 15