Species Interactions & Population Control

Five Major Interactions Interspecific Competition Predation Parasitism Mutualism Commensalism

Interspecific Competition Different species competing for the same resources Niche overlap Greater overlap = more intense competition Outcomes: Resource partitioning Evolution/speciation Competitive exclusion Local Extinction

Resource Partitioning When species divide a niche to avoid competition for resources

Competitive Exclusion two species competing for the same resource cannot coexist at constant population values, if other ecological factors remain constant

Predation

Close long term associations between two or more species Symbiosis Close long term associations between two or more species Three types: Mutualism Commensalism Parasitism

Brood Parasitism The manipulation and use of a host to raise the young of the brood parasite *Nest hypothesis *Mafia hypothesis 18:26 on video Nest hypothesis – look for similar nest & egg characteristics & sneak in – cuckoo Click nest 1st for how and hypothesis for what happens after Mafia -  Not only do these brood parasites usually differ significantly in size and appearance, but it is highly probable that they reduce the reproductive success of thei

A group of interbreeding individuals of the same species Population A group of interbreeding individuals of the same species

Population Characteristics Size Density Dispersion Age distribution

= Population Size Four variables determine population size: Births Deaths Immigration Emigration = Population Change (Births + Immigration) - (Deaths + Emigration)

Dispersion

Dispersion Clumps -most popular 1. Cluster near resources 2. Groups increase chance of finding resources 3. Protection 4. Hunting

Dispersal Examples Territorial Solitary Clumped (elephants) Uniform (creosote bush) Random (dandelions) Territorial Solitary

Age Structure Distribution of individuals among various ages Dictates how rapidly a population Three groups: 1. Pre-reproductive stage not mature enough to reproduce 2. Reproductive stage capable of reproduction 3. Post-reproductive stage too old to reproduce

A B C D

Life Tables Shows life expectancies for age groups Demography: Study of a populations vital statistics and how they change over time Life table females males The difference in life-span between male and female Richardson's ground squirrels in nature is attributable to the different reproductive strategies adopted by the two sexes. Juvenile males pursue the high-risk strategy of dispersal, emigrating from their natal area to an unfamiliar location where they encounter squirrels that are not kin. Dispersal has the reproductive advantage of avoiding inbreeding but incurs the disadvantages of traversing unfamiliar territory, exposure to predators, contact with machinery or vehicles while crossing roads, and being attacked by resident ground squirrels as they attempt to settle in a new location. Adult male Richardson's ground squirrels experience extreme pressures during the mating season due to intra-sexual competition for access to estrous females. Males engage in vigorous fights, and the resulting wounds and stress can cause fatalities. Additionally, males are less vigilant about watching for predators during the mating season. Female Richardson's ground squirrels are more sedentary and conservative in their reproductive strategies than males. Females tend to stay in a familiar location in or near their natal home range throughout their lifetime, and females do not engage in fights during the mating season. What adaptations have led to this difference in male vs. female mortality?

Exponential Growth Constant growth of a population J shaped curve Birth rate exceeds the death rate J shaped curve

Conditions for Exponential Growth Unlimited resources Abundant space Abundant food Shelter Decrease in predators Decrease in disease Reproduction

Rule of 70 How long does it take to double? Rule of 70 Resource use Population size Money in a savings account Rule of 70 70 divided by the percentage growth rate = doubling time in years 70 / 7% means it takes ten years to double

Human Population

Logistic Growth Growth of a population slows or stops as resources become less available S curve

Carrying Capacity The largest number of individuals that a given environment can support at a given time

Regulation of population size Limiting factors density dependent competition: food, mates, nesting sites predators, parasites, pathogens density independent abiotic factors sunlight (energy) temperature rainfall marking territory = competition competition for nesting sites

St. Matthew’s Island

Ecological Succession Predictable changes that occur in a community over time Two types: Primary Secondary

Begins in a place without any soil Primary Succession Begins in a place without any soil Examples: Volcanos Glacier retreats Process begins with pioneer species lichens or cyanobacteria

Primary Succession Moss move in bringing insects Ferns & grasses Shrubs & Trees

Organisms evades an ecosystem that already existed before Secondary Succession Organisms evades an ecosystem that already existed before Usually a result of disturbance Human disturbance Natural catastrophes

Steps in Secondary Succession Major disturbance – weeds come in Grasses Pines begin to grow Grasses are shaded out Old pines die – hardwoods begin to replace

Secondary Succession

Climax Community A stable group of plants and/or animals that colonize an area after a succession event Ex: Old Growth Forest

Climax Community Climax communities are not always BIG trees! Grasses in prairies Cacti in deserts

Aquatic Succession Transition of aquatic habitats (mainly ponds) filling with sediments & the eventually becoming a terrestrial ecosystem