Biodiversity, Species Interactions, and Population Control Chapter 5

HOW DO SPECIES INTERACT? Five types of species interactions—competition, predation, parasitism, mutualism, and commensalism— affect the resource use and population sizes in an ecosystem.

Species Interact in 5 Major Ways Interspecific Competition Predation (predator vs. prey) Parasitism (parasite vs. host) Mutualism Commensalism These interactions help to limit population size (illustrating one of the scientific principles of sustainability).

Competition When species struggle for the same resources Niche: the unique role of a species in an ecosystem Overlapping niches = competition Competitive exclusion principle: No two species can occupy the exact same niche for very long.

Predation

Coevolution Predator and prey populations exert intense natural selection pressures on one another Prey will develop traits that make them more difficult to catch Predators will develop traits that make them more successful hunters.

Prey defense: Camouflage

Prey defense: Chemical Warfare & Warning Coloration

Prey defense: Mimicry

Prey defense: Deceptive looks

Prey defense: Deceptive behavior

Parasitism

Mutualism

Commensalism

HOW CAN NATURAL SELECTION REDUCE COMPETITION BETWEEN SPECIES? Some species develop adaptations that allow them to reduce or avoid competition with other species for resources.

Some Species Evolve Ways to Share Resources Resource partitioning: when species competing for similar scarce resources evolve specialized traits that allow them to use shared resources at different times, in different ways, or in different places Ex. Various birds

WHAT LIMITS THE GROWTH OF POPULATIONS? No population can continue to grow indefinitely because of limitations on resources and because of competition among species for those resources

Populations Have Certain Characteristics Population dynamics Distribution Numbers Age structure Density

Most Populations Live Together in Clumps or Patches

Why Clumping? Resources a species needs vary greatly in availability from place to place, so they cluster where the resources are They help each other  finding resources, looking out for predators/prey Makes it easier for mating and raising young.

Populations Can Grow, Shrink, or Remain Stable Populations emigrate from areas where their habitat has been degraded or destroyed and immigrate to places were resources are more plentiful Change in Population Size Births + Immigration Deaths + Emigration

Population Growth Biotic potential: capacity for population growth under ideal conditions General rule  The bigger you are, the lower your biotic potential Elephants and whales have low biotic potential; bacteria have a huge biotic potential Intrinsic rate of increase: rate at which the population of a species would grow if it had unlimited resources High rate of IR growth happens when organisms: Reproduce early in life Can reproduce many times Have many offspring each time they reproduce.

Too much of a good thing…? No population can grow indefinitely because of competition for limited resources Ex. Light, water, space, nutrients, or exposure to competitors, predators or diseases Environmental resistance: combination of all the factors that act to limit the growth of a population (see-the world IS out to get you  ) Carrying capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without being degraded Biotic potential + Environmental resistance.

Mind the Curves! Unlimited resources leads to exponential growth J Curve

Mind the Curves! Logistic growth exhibits exponential growth until population reaches carrying capacity S Curve

When a Population Exceeds Its Habitat’s Carrying Capacity, Its Population Can Crash Some species do not make a smooth transition from exponential growth to logistic growth Overshoot (going beyond K) can deplete resources of habitat and populations suffer a dieback Might permanently reduce the carrying capacity of a given habitat.

R vs. K Species R-selected Species Capacity for high rate of population increase Usually have many, small offspring Tend to be opportunists  populations explode when they find ample resources Ex. Cockroaches K-selected Species Tend to reproduce later in life, and have few offspring Species tends to thrive on high competition Ex. Elephants.

R vs. K Species

Genetic Diversity Affects Small Populations (Or Lack Thereof…) Founder effect Demographic bottleneck Genetic drift Inbreeding.

Population Density Population density: the number of individuals in a population found in a particular area or volume Density-dependent population controls Greater effect with the density increases Ex. Predation, parasitism, infectious disease, competition Density-independent population controls Effect does not change with population density Mostly abiotic in nature Ex. Weather, earthquakes, etc.