Understanding Populations

What is a population? Remember, a species, such as homo sapiens, can exist in many places. The population is all the members of the species living in the same place at the same time!

Populations Note that the word POPULATION refers to the group in general AND the size of the group!!

Populations DENSITY NUMBER of individuals PER UNIT AREA (or volume) the number of individual organisms in a space This is often related to habitat quality Fluctuations in density reflect changes in the local conditions (new parasite, abiotic factors change, etc)

Dispersion Dispersion is the distribution or arrangement of organisms in the habitat Most populations are clumped. Why? Resources are not uniformly distributed Protection of the group / Pack living gives some predators greater success Temporary mating or young-rearing groups / seed distribution

Populations are Dynamic Age structure – Who can add to population? Pre-reproductive stage Reproductive stage Post-reproductive stage

Population Growth Births Deaths Growth Rate

Growth Rate How fast a population’s size changes over time is called a growth rate. Growth rates can be positive… what would that mean? Growth rates can be negative… what would that mean? Growth rates can be zero… what would that mean? Lab Time

Moving On? How do you think MIGRATION affects growth rate? Immigration would ADD to population Emigration would subtract from population

Population Growth Deaths + Emi-gration Births + Immi-gration Growth Rate

Factors affecting Growth Biotic Potential is the fastest rate at which a population can grow. Limited by reproductive potential, or the maximum number of offspring a member can produce Also limited by generation time: the average time needed to reach reproductive age.

Compare Biotic Potential Mosquito: - has thousands of kids - able to reproduce in days! - population growth? MONGO! Elephant: Has less than 10 offspring Takes 13 years before able to reproduce Population growth? Pitiful!

It’s Out Of Control! Exponential growth occurs in nature only when populations have plenty of food and space No competition or predators can exist Often occurs with exotic or invasive species! (why??) La vache dit, comme ci.

Wascally Wabbits! Australia’s Mccaw Island After rabbits were introduced… Where’s Elmer Fudd when you need him??

Population Regulation What causes exponential growth to be limited? Limiting Resource Habitat loss Disease Disaster (natural or manmade) Competition Predator-Prey relationships

Limiting Resources The natural resource that inhibits growth is called the LIMITING RESOURCE. Habitat loss can increase potential candidates for this Competition, disease, and predation also limit population growth. Many times, members of a species will carve out TERRITORY to avoid competition How do different species mark out territory? Birds? Dogs? Trees?

Population Regulation Habitat Loss is also listed as a means in which growth is inhibited How would this affect population growth? It would speed up the use of the limiting resource, increasing death rate.

CARRYING CAPACITY The theoretical limit that a habitat can support is called the carrying capacity. What pattern do you see over there ?

A Closer Look - Activity! Environmental resistance Carrying capacity (K) Population size (N) Population stabilizes Exponential growth Biotic potential Time (t)

Population Regulation Beyond resource and habitat limitations, other factors, such as disease and disaster can regulate populations We divide all population limiting factors into DENSITY DEPENDENT and DENSITY INDEPENDENT regulation

Population Regulation Density Dependent Definition: deaths occur more quickly when population is crowded. Most limiting factors are density dependent. Example – disease: needs to spread from organism to organism. Example – competition: the more individuals in an area, the less of a resource is available to each.

Population Regulation Density Independent When the cause of death is density INDEPENDENT, a proportion of the population will die, regardless of congestion. Weather and disasters are examples Let’s Classify Some, shall we?

No Man Is An Island Species are never alone in an ecosystem. In order to survive, any population must carve out its unique role within the ecosystem – called its NICHE. A niche includes the species’ physical home, the environmental factors necessary for the species’ survival, and all the species’ interaction with other organisms!

Inter Species Relationships The Way that SPECIES INTERACT can accentuate or inhibit population growth. We’ve discussed these relationships before, but now we’re going to study them in depth

Symbioses: Ways Species Interact Interaction Species A Species B Description Competition Harmed Each species negatively impacts the other Predation and Parasitism Benefited Species A feeds on Species B Mutualism Each species is helpful to the other Commensalism Unaffected Species A benefits from species B, Species B is unaffected Amensalism Species A may benefit from the death of species B

Symbiosis and Coevolution A relationship in which two organisms live in close association is called symbiosis Usually, at least one of the organisms benefits Over time, species in close relationships may coevolve – that is, they evolve adaptations that reduce the harm or improve the benefit of the symbiotic relationship As we go through relationships, see if you can spot the coevolutions!

Species Interactions Predation Competition Parasitism Amensalism Mutualism Commensalism

Competition Competition is a relationship in which different INDIVIDUALS OR POPULATIONS attempt to use the same limited resource. It occurs within and between species When species compete, we say their niches overlap.

Name the Resource Competition On the left, competing for sunlight. On the right, two different versions of barnacles competing for food.

Indirect Competition Species can compete even if they never come in contact. Day feeders and nocturnal animals may all use the same water hole – they are indirectly competing. Humans rarely interact with potato bugs, but we’re in competition for potatoes.

Adaptations to Competition In the course of evolution, adaptations that decrease competition will be advantageous when niches overlap. Niche restriction is when each species uses LESS of the niche than they are capable of using (for example, territory restriction)

Barnacles use only one part of intertidal zone

Species Interactions Predation Competition Parasitism Amensalism Mutualism Commensalism

Predation An organism that feeds on another organism is called a predator. The organism that is fed upon is the prey. This interaction is predation. This is NOT as simple as it seems. Sometimes predators are prey! Most organisms have developed predation defense mechanisms.

Population Curve Reminder

And a long term relationship!

Species Interactions Predation Competition Parasitism Amensalism Mutualism Commensalism

Parasitism An organism that lives in or on another organism and feeds on the other organism is called a parasite. The organism that the parasite steals nourishment from is called the host. Parasites are somewhat like predators, the difference being that parasites live IN or ON the host. Predators only eat the host.

Plant parasites!

Animal Parasite… the flea

Common parasites of the human body (1) The hookworm latches on the walls of the colon with its sharp teeth where it feeds on blood. (2) The tapeworm is the longest parasite. A mature adult can lay a million eggs a day. (3) Tapeworm eggs embedded in the colon. (4) The roundworm can grow to be 20 inches (50 cm) long and lay 200,000 eggs per day. (5) Pinworms migrate outside the colon during the night to lay their eggs around the anus. This causes the nightly itching of many unsuspecting victims.

Species Interactions Predation Competition Parasitism Amensalism Mutualism Commensalism

Mutualism A close relationship between two species in which each species provides a benefit to the other is called mutualism Algae in coral is mutualistic The bacteria in your gut is mutualistic

Name the benefits!

Species Interactions Predation Competition Parasitism Amensalism Mutualism Commensalism

Commensalism When one species benefits, but the other species is unaffected, the relationship is called COMMENSALISM. Remoras, for example, either hitch a ride on bigger animals, or they eat food scraps from the bigger animal, or both… Mimicry can be another type – One organism looks like another, for a reason. They benefit, and the ones they mimic are unaffected.

Remoras!

Mimicry 1: why?!

Mimicry2 – Why?! Warning Coloration vs Camouflage

More Mimicry!

Species Interactions Predation Competition Parasitism Amensalism Mutualism Commensalism

Amensalism A symbiotic relationship in which one species is unaffected but the other is harmed. Often, the second species is actually terminated. Think about grass being tramped by people. Sometimes, the surviving species uses the nutrients from the terminated species, so there is benefit. As an example, many plants secrete substances that inhibit or kill neighboring plants! They then may use the detritus of the dead plants as nutrition!

Plant Amensalism The Black Walnut Penicillium! Black walnuts and penicillium both exude liquids that kill other plants or animals.