CHAPTER 5Populations and Communities

Standard 3

Standard 3: Students know and understand the characteristics and structure of living things, the processes of life, and how living things interact with each other and their environment.

3.16: An organism’s adaptations (for example structure, behavior) determine its niche (role) in the environment.

3.16a: Predict the niche of an organism based on physical and behavioral characteristics.

Vocabulary

Population Carrying capacity Predation Coevolution Parasitism Symbiosis Mutualism Commensalism

Niche Fundamental niche Realized niche Competitive

exclusion Keystone species

Videos approximately 55 minutes

What is a population?

A population is a group of organisms of the same species that live in a specific geographical area and interbreed.

Population growth is important because populations of different species interact and affect one another, including human populations.

In the 1850’s two dozen rabbits were introduced from Europe. By the 1950’s there were 600,000,000 rabbits. What conditions were favorable for this huge growth?

Population Growth (5:00)

Whether a population grows or shrinks depends on births, deaths, immigration and emigration.

Immigration is movement of individuals into a population.

Emigration is the movement of organisms out of a population.

Exponential growth occurs when numbers increase by a certain factor in each successive time period. This is indicated by a J-shaped curve.

Carrying Capacity Populations do not grow

unchecked forever. Eventually due to food availability, predators and disease, the growth will slow and may stabilize.

The largest population that an environment can support at any given time is called the carrying capacity.

Density-independent factors are variables that affect a population regardless of population density, like fires, floods, weather.

Logistic growth is population growth that starts with a minimum number of individuals and reaches a maximum depending on the carrying capacity of the habitat.

Factors That Affect Population Size

Abiotic factors are non-living factors that affect a population. Weather and climate are the most important. This includes water availability.

Biotic factors are living factors. Food, predators, and human activity affect populations.

Common Abiotic Factors (6:35)

Biotic Factors (3:57)

Human Population Today, human population is 6.8 billion

and increasing. Better sanitation, hygiene, disease

control and technology have decreased the rate of death for human populations. What kind of graph is this, logistic or exponential?

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Interactions in Communities

Predation is the act of one organism killing another for food.

Most animals are both predator and prey. Exceptions are very large species like killer whales that are not hunted by other species.

Predation: (5:00)

Animal Predators and the Balance of Nature

(14:08)

Wolves of Yellowstone

Coevolution Many interactions

between species are the result of a long evolutionary history.

Species that involve predator-prey or parasite-host relationships often develop adaptations in response to one another.

This back and forth evolutionary adjustment between two species is called coevolution.

Evolution coevolution of the ant and fungi (5:13)

Parasitism (1:21)

A parasite is an organism who is dependent upon a host.

The host is always larger than the parasite.

Indian paintbrush (Castilleja indivisa) is a parasitic plant that obtains some of its nutrients and water from host plant--bluebonnet (Lupinus texensis).

Indian paintbrush and bluebonnet

Herbivory Herbivores eat plants, but

don’t generally kill them. However, plants do have

defense mechanisms, like thorns or chemical compounds that make herbivores sick or kill them.

Monarch butterflies have adapted so they can eat milkweed that is poisonous to other animal species, thus keeping them from being eaten by birds.

Mutualism

Mutualism is a mutually beneficial relationship between organisms.

The bee feeds on the flower and pollinates it at the same time. Both benefit.

Coral Reef Ecosystem

Bee and flower

Commensalism

Commensalism occurs when one organism benefits from another without aiding or harming the host.

Remoras are “hitchhiker” fish that eat the leftovers of larger fish. They don’t help or hurt the fish, so it’s a commensal relationship.

Whaleshark and remora

Decomposers (0:54)

When any organism dies, it is eventually eaten by detrivores (like vultures, worms and crabs) and broken down by decomposers (mostly bacteria and fungi), and the exchange of energy continues.

Niche Where a habitat is the place

where an organism lives, a niche describes how an organism fits into an ecosystem.

A fundamental niche is the entire range of conditions where an organism or species could survive.

Competition for resources between species, shapes a species’ fundamental niche.

The actual niche a species occupies is called the realized niche.

Some species will steal food from one another—this is called kleptoparasitism.

Niches (1:33)

Competitive Exclusion

Two species that are too similar cannot coexist because one of the species will be slightly better at acquiring resources.

Thus, the less successful species will either die off or move away.

One species eliminating another through competition is called competitive exclusion.

Competitive exclusion and resource Partitioning (4:10)

Dividing Resources

Sometimes, competitors eat the same thing found in the same place or fundamental niche.

In some cases, they will share or divide resources thus creating their own smaller, realized niche.

Example: Birds of the same species will divide resources up in various parts of a tree.

Ecosystem Resiliency

Interactions between organisms and the number of species in an ecosystem add to the resiliency of an ecosystem.

A keystone species is a species that is critical to an ecosystem because the species affects the survival and number of many other species in its community.

Mud Shrimp (3:01)

Sea Otters (2:13)