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Symbiosis Mutualism | Commensalism | Parasitism Learning Objectives • Compare and contrast the three types of symbiosis • Evaluate relationships to determine the type of symbiosis occurring Mutualism • Symbiosis – a close ecological relationship between two species • Types of symbiosis – Mutualism – Commensalism – Parasitism • Mutualism – an ecological relationship in which both species benefit – Ex) Bees gain food, flowering plants gain gamete diversity Commensalism • Commensalism – an ecological relationship in which one species benefits and the other is not affected – Ex) Barnacles gain nutrients, whales are not affected Parasitism • Parasitism – an ecological relationship in which one species benefits and the other is harmed • Host – the organism that is harmed by the parasite • Parasite – the organism that benefits from the host • Ex) Tick gains nutrients, dog loses blood and may be exposed to disease Types of Symbiosis Type of Symbiosis Mutualism Commensalism Parasitism Species One Species Two Determining Types of Symbiosis • To determine the type of symbiosis Step 1 Write the names of the two species. Step 2 Determine how the first species is affected. Step 3 Determine how the second species is affected. Step 4 Determine the type of symbiosis occurring. Determining Types of Symbiosis Example Ex) A fungus is found on the bottom of some people’s feet. The fungus absorbs nutrients from the human it grows upon. The fungus is not fatal. What ecological relationship does this represent? Step 1 Write the names of the two species. Step 2 Determine how the first species is affected. Human Fungus Human Fungus Step 3 Determine how the second species is affected. Human Fungus Step 4 Determine the type of symbiosis occurring. Parasitism Does the result make sense? Yes. Graphing Symbiosis • Ecologists determine the type of symbiosis occurring by graphing the populations of the two species over time Community Dynamics Predator-Prey Relationships | Limiting Factors & Carrying Capacity Learning Objectives • Describe predator-prey relationships • Recognize how limiting factors affect populations • Explain rates of growth in a population Predator-Prey Relationships • Predation – relationship in which one organism hunts and kills another for nutrition • Predator – an organism which hunts and kills another organism (ex: bear and snake) • Prey – the organism which is killed by the predator (ex: fish and frog) Predator-Prey Relationships • Prey populations determine predator populations – As hare (prey) population increases, lynx (predator) population increases – As hare (prey) population decreases, lynx (predator) population decreases Predator-Prey Relationships Late 1960s 1. An increase in moose population causes increase in wolf population. 2. Increased wolf population causes decrease in moose population. 1980 1. Wolf population is decimated by disease. 2. Decreased wolf population allows moose population to increase. Limiting Factors and Carrying Capacity • Biotic potential – the highest rate of reproduction possible for a population under ideal conditions • Exponential growth – extremely high rate of growth experienced by a species that reaches its biotic potential • Limiting factors keep growth rates in check – Limiting factors – external factors or environmental conditions that affect population size Limiting Factors and Carrying Capacity • Density-dependent factors – natural resources that affect population growth as a result of density – Ex) Food, water, and space, predation, disease, and availability of mates • Density-independent factors – environmental conditions that affect a population regardless of its density Limiting Factors and Carrying Capacity • Density-independent factor: weather – Grey squirrels must find shelter during the winter – Does not depend on the density of the population Limiting Factors and Carrying Capacity • Density-independent factor: human activities – A new dam affects all densities of populations Limiting Factors and Carrying Capacity • Population Growth – Growing populations have a positive growth rate – Decreasing populations have a negative growth rate – Populations that are neither growing nor decreasing are in a state of equilibrium • Carrying capacity – the point at which a population reaches a state of equilibrium and there is no net gain or loss of individuals Limiting Factors and Carrying Capacity 1. Initially, populations have exponential growth. 2. Limiting factors slow population growth. 3. Population reaches its carrying capacity. Community Dynamics External Dynamics | Competition Learning Objectives • Analyze how organisms, populations, and communities respond to external factors • Compare interspecific and intraspecific competition External Dynamics • Populations constantly change • Factors that affect population size – Births – increase population size – Deaths – decrease population size – Immigration – increase population size • Immigrate – the movement of organisms into an area – Emigration – decrease population size • Emigrate – the movement of organisms out of an area External Dynamics • External factors and environmental conditions – Directly affect organisms, populations, and communities – Affect the availability of resources • Organisms must adapt in order to survive External Dynamics • Natural disasters – Forest fires, hurricanes, floods, droughts, and earthquakes – Affect organisms and resources • Community impact – Populations are interrelated and affect one another Competition • Competition – occurs when two organisms require the same resource to meet their needs • Organisms must compete for resources to survive Competition Dynamics 1. 2. 3. 4. Food is scarce for deer in winter. Competition increases in deer population. Deer population decreases. Wolves feed on deer. – Competition increases over scarce deer. 5. Competition contributes to limited population growth for both the deer and wolf populations. Competition • Intraspecific competition – organisms of the same species compete for resources within the ecosystem – Ex) Diatoms grown in lab compete for space and light – Leads to population decrease Competition • Interspecific competition – occurs between different species for resources within an ecosystem – Keeps the growth rate of populations in check