Ecology

Question 1

Define:

ecology

Answer 1

The study of the relationships between organisms and other organisms, as well as between organisms and their environments.

Question 2

Define:

population

Answer 2

A group of organisms of the same species that live in a particular location and interbreed.

For example, the humans living in a certain town would constitute a population.

Question 3

Define:

community

Answer 3

A group of multiple populations of different species that live in the same area.

For example, the humans, birds, non-human animals, insects, etc. living in a certain town could constitute a community.

Question 4

What is the difference between a community and an ecosystem?

Answer 4

• Community includes only living organisms, specifically those living and interacting in a particular area.
• Ecosystem includes both these living organisms and the non-living components around them.

For example, an ecosystem could include rocks, soil, air, and water.

Question 5

What term describes the fraction of the earth where living things can be found?

Answer 5

biosphere

The biosphere actually represents a fairly small proportion of the earth’s volume, as no life can survive in the earth’s core or even moderately far below the surface. Note that the biosphere also includes water and air where living organisms exist.

Question 6

Define:

niche

Answer 6

The position it occupies in its larger community. A niche can include the organism’s diet, habitat, and/or reproductive patterns.

A niche can also be remembered as all of the ways the organism interacts with both living and non-living parts of its environment.

Question 7

Name the four major trophic levels of the food chain.

Answer 7

1. producers
2. primary consumers
3. secondary consumers
4. tertiary consumers

These levels categorize organisms based on their food sources (plants or other animals). Together, the levels constitute the food chain, a depiction of the way energy moves from one organism to the next in an ecosystem.

Question 8

In population ecology, what defining feature characterizes producers?

Answer 8

These are autotrophs, or organisms that produce their own nutrients, generally using light from the sun. Most plants are a classic example of producers.

Producers are found at the bottom of the food chain, where they are consumed by primary consumers.

Question 9

An herbivore would be categorized in which trophic level of the food chain?

Answer 9

primary consumers

Remember, plants are producers, or organisms that can make their own nutrients using light energy. Organisms that eat producers are termed primary consumers.

Question 10

Secondary consumers feed on organisms from which trophic level of the food chain?

Answer 10

primary consumers

Primary consumers are plant-eaters, or herbivores. Secondary consumers feed on these animals, making them examples of carnivores (meat-eaters).

Question 11

Tertiary consumers feed on organisms from which trophic level of the food chain?

Answer 11

secondary consumers

Remember, secondary consumers are carnivorous animals that eat primary consumers (herbivores). Since tertiary consumers then feed on secondary consumers, we can think of tertiary consumers as “carnivores that eat carnivores.”

Question 12

When a secondary consumer feeds on a primary consumer, what percent of the energy from the primary consumer is transferred to the animal that consumes it?

Answer 12

10%

Remember this value! In a typical food chain, only about 10% of the energy in a particular trophic level is transferred to the level above it via consumption. Most of the remaining energy is used up by the metabolic reactions of the animals or plants prior to being consumed.

Question 13

A certain ecosystem is introduced to a toxic pesticide for an extended period. The highest concentrations of this toxin will likely be found in organisms from which trophic level?

Answer 13

Tertiary consumers

As you move up the food chain, you’ll tend to observe higher levels of environmental toxins. Tertiary consumers are carnivorous animals who eat other carnivores, so they are found at the top of the chain. Since these animals must eat large numbers of the animals below them, and those animals eat large numbers of the animals below them, they also tend to consume large amounts of toxins.

Question 14

The diagram shown here categorizes plants and animals based on their feeding habits. What name is given to this type of diagram?

Answer 14

ecological pyramid

Ecological pyramids are used by ecologists to depict the trophic levels of an ecosystem. Note that these pyramids can vary in shape; you may also see them as images with stacked horizontal lines, where the longer the line, the more energy held by that particular level.

Question 15

How do saprobes obtain nutrients?

Answer 15

They decompose decaying organic matter in their surroundings. For this reason, these organisms are also called decomposers.

Saprobes include fungi (the classic example you’d most likely see on the AP Biology exam) and certain bacteria.

Question 16

Define:

symbiosis

Answer 16

It occurs when two or more species live and closely interact with each other.

These interactions include those where both species benefit, where one benefits and the other is left unharmed, and where one benefits by harming the other.

Question 17

Name the three types of symbiotic relationships.

Answer 17

1. mutualism
2. commensalism
3. parasitism

Symbiosis always benefits at least one species; these categories are defined by its effect on the other.

Question 18

Define:

mutualism

Answer 18

A type of symbiosis in which both species benefit from the relationship.

Humans and intestinal bacteria mutually benefit from this type of symbiosis.

Question 19

Define:

commensalism

Answer 19

A type of symbiosis in which one species benefits and the other is unaffected.

One example is the relationship between clownfish and anemones. The fish use the anemones for shelter and protection without impacting the anemones themselves.

Question 20

Define:

parasitism

Answer 20

A type of symbiosis in which one species benefits and the other suffers a varying degree of harm.

Tapeworms, which both feed off and sicken their human hosts, are examples of parasites.

Question 21

Bees collect and eat nectar from flowers, moving pollen to other flowers in the process. Which symbiotic relationship does this exemplify?

Answer 21

mutualism

The bees benefit by having a source of food, while the flowers reproduce via the spreading of pollen.

Question 22

Egrets (birds) often follow herds of cattle and eat insects the cattle stir up in the grass. Which symbiotic relationship does this exemplify?

Answer 22

commensalism

The egrets benefit from easier exposure to a food source, but the cattle are unaffected by the presence of the birds.

Question 23

Name four properties of populations that are important in the study of population ecology.

Answer 23

The four properties typically studied by population ecologists are:

1. population size (N)
2. population density
3. dispersion/distribution patterns (how “spread out” the organisms are)
4. age structure

Question 24

In population ecology, what two quantities are plotted on a typical survivorship curve?

Answer 24

It plots the percent of surviving organisms in a population versus the age of the organisms.

Percent of surviving organisms is displayed on the y-axis, while age is plotted along the x-axis. The resulting curve gives information about the population trend, whether members tend to die young, experience a constant mortality rate over their lifespans, etc.

Question 25

The growth rate of a population can be calculated using what formula?

Answer 25

r = (births - deaths) / N

Here, r represents the growth rate or “reproductive rate,” and N denotes the size of the population at the beginning of the interval in question. For example, if a 4000-individual population experienced 85 births and 45 deaths during a particular interval, r would be equal to (85 - 45) / 4000 = 40/4000 = 0.01.

Question 26

Define:

biotic potential

Answer 26

It is the potential of a population is its maximum possible growth rate, assuming ideal conditions.

Biotic potential is determined by multiple factors, including the frequency of reproduction, number of offspring that can be had at a time, and offspring survival rate.

Question 27

Define:

carrying capacity

Answer 27

The largest number of individual organisms from a certain population that a habitat can sustain.

For example, if a twenty-acre forest region under ideal conditions can only hold 40 white-tailed deer, then 40 is the carrying capacity for that population and habitat. Note that carrying capacity is rarely reached in reality.

Question 28

As the number of individuals per unit area increases, certain factors begin to have greater and greater limiting effects on the population. These factors are termed:

Answer 28

density-dependent limiting factors

In general, limiting factors are agents that prevent a population from growing as rapidly as it otherwise would. Density-dependent factors are those that increase in effect as the population density rises. A classic example of this is starvation.

Question 29

A severe blizzard that kills many members of a rabbit population represents which type of limiting factor?

Answer 29

density-independent limiting factor

Density-independent factors are those that occur with equal frequency regardless of the density of the population. Since there is no logical way that population density could affect the likelihood of a blizzard striking, this factor is density-independent.

Question 30

Name the two classic patterns of population growth.

Answer 30

Exponential and logistic growth

Exponential growth is observed in ideal situations, when the population can grow very rapidly. For example, consider bacteria growing on a fresh agar plate - they have no competition and abundant resources, so steep exponential growth can occur. In contrast, logistic growth occurs when limiting factors arise and keep the population size at its carrying capacity.

Question 31

What is the key distinction between R-selected and K-selected species?

Answer 31

• R-selected species (or r strategists) mature quickly and yield many offspring. This leads to rapid exponential growth. R-selected species typically prefer barren habitats with abundant resources.
• K-selected species (or K strategists) mature slowly and have few offspring. These species typically display logistic (slow) growth and can occupy crowded environments, as they tend to have little competition.

Question 32

A species of mammal is known for its devoted parenting, with mothers usually taking care of their young for several years. Is this species most likely an r-strategist or a K-strategist?

Answer 32

K-strategist

K-strategist species are those that have few offspring, but generally invest a large amount of time and resources into their parenting. In contrast, r-strategists have many offspring that mature quickly; these species expend little-to-no parenting effort.

Question 33

Define:

ecological succession

Answer 33

The relatively predictable change in the species composition of a community over time.

As this process continues, the diversity of species tends to increase.

Question 34

A species of lichen is the first population to grow on the barren soil of a forest that burned down years ago. What role does this species play in ecological succession?

Answer 34

pioneer species

Pioneer species are the first species to begin growing in an entirely new or previously damaged habitat. Their growth begins the process of ecological succession. Lichens are classic pioneer species, as they can grow even in harsh, rocky environments.

Question 35

If humans or other life-forms were suddenly able to grow on Mars, and if life continued to thrive there for centuries as the composition of species gradually changed, would this represent primary succession or secondary succession?

Answer 35

primary succession

Ecological succession refers to gradual, fairly predictable changes that occur to the species composition of a habitat. This process is termed primary succession if no species have inhabited the area before, which is the case on Mars.

Question 36

A climax community is likely to include ___-selected species, while a pioneer species is likely to utilize ___ selection.

Answer 36

The climax community would likely include K-selected species, while the pioneer species would likely be r-selecting.

In ecological succession, a climax community is the final, stable community that occupies an area. This community tends to include K-selecting species, which display slow growth and have few offspring. In contrast, a pioneer species is the first species to colonize a barren area. These species are typically r-selecting, meaning that they have many offspring and grow exponentially; this fast growth helps the species colonize the area rapidly.

Question 37

What specific adverse effects have humans had on the biosphere?

Answer 37

Humans have affected our environment in countless ways. Here are a few that you should know for the AP Biology exam:

• Climate change/depletion of the ozone layer
• Pollution, and results of pollution (including acid rain)
• Deforestation
• Desertification (loss of grasslands due to overgrazing of livestock)
• Loss of biodiversity

Question 38

An ethologist is a specialist in what field of study?

Answer 38

They study animal behavior, including learning, aggression, mating, and communication.

Animal behavior is tested on the AP Biology exam, although you likely won’t see more than two or three questions about it. Still, it’s important to understand the basics.

Question 39

Broadly speaking, in what two ways can animal behavior develop?

Answer 39

Animal behavior can either be genetic (innate/unlearned) or learned (acquired through interaction with stimuli in the environment).

Learned behaviors can also be taught; for example, many animal species teach their offspring behaviors related to food acquisition.

Question 40

Define:

instinct

Answer 40

A behavior that is innate (not learned). Animals perform instinctual behavior naturally, often in response to a particular stimulus.

Instincts tend to guide behavior in very young organisms (although some organisms are guided by instinct for their entire lives). In humans, a classic instinct is the urge an infant has to suckle.

Question 41

Name two types of associative learning that may be observed in animals.

Answer 41

classical conditioning and operant conditioning

Associative learning involves association between one or more stimuli and one or more responses.

Question 42

Define:

classical conditioning

Answer 42

A form of associative learning in which a neutral stimulus is paired with a second stimulus that typically elicits a particular response. Over time, the neutral stimulus alone will start to elicit that same response.

A classic example is found in Pavlov’s experiments with dogs. Pavlov paired the sound of a bell (the neutral stimulus) with the presentation of food (a stimulus that naturally caused the dogs to salivate). Over time, the dogs would begin to salivate in response to the sound of the bell alone. The bell had become a “conditioned stimulus.”

Question 43

Define:

operant conditioning

Answer 43

A form of associative learning in which behavior changes in response to rewards or punishments.

For example, imagine that you give your cat food each time it meows repeatedly. Since food is a reward, the cat may begin meowing repeatedly more often, so it can obtain more food. The reward has thus increased the frequency of the cat’s behavior.