- Interactions between species may be positive, negative, or neutral
- Interspecific interactions affect population dynamics and species distributions
- Interactions affect individual fitness and can result in evolution
- Intraspecific-two individuals within the same species
- Interspecific-among individuals of different species
- Interactions influence population densities, alter species distributions, and lead to evolutionary change
- Help or harm?
- Competition (-/-)
• both exert energy
• Use or defines of a resource by an individual that decreases the resource availability to others
- food, water, nutrients, space
- any factor consumed by an organism and supports increased population growth rates
• Intraspecific/Interspecific
• over a limiting factor, where competition for a single resource is most intense
• Competitive exclusion principle-2 species often cannot coexist indefinitely on the same limiting resource
• presence of a competitor always reduces population growth rate
• when two species coexist, they have lower equilibrium population densities than either would alone
• Competition may cause one species to go extinct
• Competition modifies per capita growth rates
- density-dependent population growth reflects intraspecific interactions among individuals in a population
- interspecific competition-effect of other species subtracted in the growth model
Consumer-resource (+/-)
• Predation
• Herbivory
• Parasitism
• Disease
Mutualism (+/+)
• fungi-plants
Commensalism (+/0)
• cattle walking field-helps birds find bugs etc.
Amensalism (-/0)
• elephants and plants
Natural systems
• coexistence of species more common: each species occupying a niche
• resources are partitioned so that there is little direct competition for the same resource
Interspecific interactions can affect the distribution of species
competitive interactions can restrict the habitats in which species occur
species interactions can affect individual fitness
Phenotypes that gain the most from a positive interaction or suffer least from a negative interaction will increase in frequency in the population and the population will evolve
resource partitioning-different ways of using a resource
• if differences in resource use are sufficiently large, competing species can coexist
Intraspecific competition can be greater than interspecific competition
Predators and species coexistence
• mussel dominates when starfish is removed-starfish allows other species to survive
• “evolutionary arms race”
- prey continually evolve better defenses and predators continually evolve better offences
• Red queen hypothesis
- predator try to outrun prey, prey outrun predator
• predator hunting strategies
- active hunt
- ambush hunting
• Evolution of defenses
- behavioral-ex. be still
• alarm calling, spacial avoidance
- crypsis- look like something else -camouflage
- Structural
• mechanical defenses
• maybe phenotypically plastic -only induced when prey detects predator
- chemical
• spray foul smelling or toxic chemicals
• store toxins in body
• warning coloration (aposematism)
- distastefulness evolves in association with conspicuous colors and patterns
- mimicry
• batesian mimicry-palatable species evolve warning coloration that resemble unpalatable species
• some passionflower species have leaf structures that resemble butterfly eggs. females will not lay eggs when there are already eggs
• Cost of defenses
- behavioral-reduce feeding activity or increase crowding in locations away from predators
- mechanical/chemical-energetically expensive to produce
- presence of predators can indirectly reduce prey population size due to cost of induced defenses reducing growth and reproduction of prey
• Counter adaptations of predators
- behavior
- camouflage
- high-speed locomotion
- resistance to toxins
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