Which of the following is a population? 1. Green sea turtles nesting on a beach 2. A flock of cardinals, geese, flamingos, and sparrows 3. Aquatic insects in the Coosa River A population is all the members of a species living in the same place at the same time.

Properties of populations 1. Size = # of individuals 2. Density = # of individuals/area 3. Dispersion - How members of a population are spread in space Regular Random Clumped

How does a population grow? What adds to a population? Births Immigration What subtracts from a population? Deaths Emigration Change in population size = (B+I)-(D+E)

EXAMPLES/PRACTICE All numbers are per 1,000 people: e.g. 6 births per 1,000 people would give a birth rate = 6/1,000 Why report births per thousand?

How fast can a population grow? Fastest rate possible = biotic potential Which has greatest biotic potential? Humans or fruit flies? Fruit flies Humans or sparrows? sparrows Humans or sea turtles? Sea turtles In general, the more offspring an organism can have at one time, the greater its biotic potential.

How fast can a population grow? Organisms with high biotic potential: Tend to: Be small Produce lots of offspring at one time Have short generation times Become sexually mature early

Populations sometimes grow exponentially Simply put: a population that grows at a fixed percentage each year. = constant rate

Example of exponential growth Money in an account earning a fixed rate of interest. e.g. $100 invested at 5% interest: Yearbalancechange (from previous year)

Human population growth year =1 billion

What limits population growth? Populations don’t grow exponentially forever. Why not? LIMITING FACTORS = Limiting resources: one or more natural resources that are not abundant enough to support continued growth.

Populations have a carrying capacity Carrying capacity is the size of a population that can be sustained over time.

Populations are regulated in 2 ways Density dependent: when deaths of population members are more common in a crowded population than in a sparse population. Density independent: when deaths are equally likely in a crowded or sparse population.

How species interaction with each other 5 main kinds Competition-/- Predation+/- Parasitism+/- Mutualism+/+ Commensalism +/0

Competition What is it? Different individuals attempt to use the same limiting resource(s) Such as: Food Water Shelter Mates Nesting sites

Competition KEY POINT: Both individuals harmed in competition, because both have reduced access to a limiting resource, even if one individual ultimately gets the resource. 2 nd key point: Competition can be both within and between species When members of different species compete, we say that their niches overlap.

Competition Competition can be indirect Two individuals might never come in contact with each other and still compete Examples?

Competition KEY POINT: The more similar species are in their niches, the greater the competition between them. To avoid competition, species sometimes shift their niche

Predation One organism feeds upon another, and kills it. Specialists vs generalists Specialist examples? Lynx eats mostly snowshoe hares Generalist examples? Praying mantises and spiders both eat any vulnerable insect

Predation Specialists

Predation Generalists Above: praying mantis Right: crab spider Both: sit-and-wait predators. Eat whatever comes along that they can catch.

Predation Prey may adapt to better avoid predation. Predators may adapt to better catch prey.

Predation Prey adaptations Camouflage Thorns (physical defense) Speed Bad taste/poison (chemical defense)

Predation

Parasitism Like predation, is +/- BUT, unlike predation, parasite doesn’t kill host. Why not?

Parasitism Parasites may be Internal: e.g., round worms, bacteria,, protozoan insect larvae External: e.g., ticks

Parasitism Schistosomiasis is disease caused by parasitic blood flukes

Parasitism Special case: parasitoid Usually a wasp or fly that lays an egg in an insect host, which eventually kills the host

Mutualism When two species benefit each other +/+ interaction Sometimes, the two species (or one of them, at least) can’t live without the other. One example: bacteria in our guts (they can’t live without us; we might get ill or lose weight without them)

Mutualism Ant-acacia in Central America Many acacias have chemical defenses Some don’t, and these have evolved a mutualistic relationship with stinging ants, which live inside the thorns Ants defend the tree against herbivores; tree provides food

Commensalism One species benefits NO EFFECT on the other species

Commensalism Examples Cows and Cattle egrets Sharks and remoras

Symbiosis and Coevolution A relationship in which two organisms live in close association is called symbiosis. Examples: Honey bees and flowering plants Over time, these two organisms may evolve adaptations that reduce the harm or improve the benefit of the relationship.