Ecology is the study of the relationships between organisms and other organisms, as well as between organisms and their environments.
In ecology, a population is 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.
In ecology, a community is 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.
What is the difference between a community and an ecosystem?
A community includes only living organisms, specifically those living and interacting in a particular area. An ecosystem includes both these living organisms and the non-living components around them.
For example, an ecosystem could include rocks, soil, air, and water.
What term describes the fraction of the earth where living things can be found?
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.
In ecology, an organism's niche is the position it occupies in its larger community. A niche can includes 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.
Name the four major trophic levels of the food chain.
The four major trophic levels of the food chain are producers, primary consumers, secondary consumers, and 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.
In population ecology, what defining feature characterizes producers?
Producers 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.
An herbivore would be categorized in which trophic level of the food chain?
Herbivores, or plant-eating organisms, are 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.
Secondary consumers feed on organisms from which trophic level of the food chain?
Secondary consumers feed on primary consumers.
Primary consumers are plant-eaters, or herbivores. Secondary consumers feed on these animals, making them examples of carnivores (meat-eaters).
Tertiary consumers feed on organisms from which trophic level of the food chain?
Tertiary consumers feed on 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."
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?
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.
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?
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.
The diagram shown here categorizes plants and animals based on their feeding habits. What name is given to this type of diagram?
This is an 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.
How do saprobes obtain nutrients?
Saprobes 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.
Symbiosis 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.
Name the three types of symbiotic relationships.
The three types of symbiosis are mutualism, commensalism, and parasitism.
Symbiosis always benefits at least one species; these categories are defined by its effect on the other.
Mutualism is a type of symbiosis in which both species benefit from the relationship.
Humans and intestinal bacteria mutually benefit from this type of symbiosis.
Commensalism is 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.
Parasitism is 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.
Bees collect and eat nectar from flowers, moving pollen to other flowers in the process. Which symbiotic relationship does this exemplify?
This is mutualism.
The bees benefit by having a source of food, while the flowers reproduce via the spreading of pollen.
Egrets (birds) often follow herds of cattle and eat insects the cattle stir up in the grass. Which symbiotic relationship does this exemplify?
This is commensalism.
The egrets benefit from easier exposure to a food source, but the cattle are unaffected by the presence of the birds.
Name four properties of populations that are important in the study of population ecology.
The four properties typically studied by population ecologists are:
- population size (N)
- population density
- dispersion/distribution patterns (how "spread out" the organisms are)
- age structure
In population ecology, what two quantities are plotted on a typical survivorship curve?
A survivorship curve 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.
The growth rate of a population can be calculated using what formula?
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.
The biotic 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.
Carrying capacity is 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.
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:
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.
A severe blizzard that kills many members of a rabbit population represents which type of limiting factor?
The blizzard is a density-independent limiting factor.
In general, limiting factors are agents that prevent a population from growing as rapidly as it otherwise would. 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.
Name the two classic patterns of population growth.
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.