Julianne Zedalis; John Eggebrecht

Learning Objectives

In this section, you will explore the following questions:

What is ecology, and what are the four levels of ecological research?
What are examples of the ways in which ecology requires the integration of different scientific disciplines?
What are examples of biotic and abiotic components of the environment?

Connection for AP^® Courses

Ecology is the study of the interactions among living organisms and with their environment. This includes relationships between organisms of the same species and also between different species. One core goal of ecology is to understand the distribution and abundance of organisms that inhabit the Earth. Ecology integrates multiple scientific disciplines in addition to biology, including molecular biology, physiology, evolution, biodiversity, geology, and climatology. Some ecological research also applies aspects of chemistry and physics, and it frequently uses mathematical models.

Information presented and the examples highlighted in the section support concepts outlined in Big Idea 4 of the AP^® Biology Curriculum Framework. The AP^® Learning Objectives listed in the Curriculum Framework provide a transparent foundation for the AP^® Biology course, an inquiry-based laboratory experience, instructional activities, and AP^® exam questions. A learning objective merges required content with one or more of the seven science practices.

Big Idea 4	Biological systems interact, and these systems and their interactions possess complex properties.
Enduring Understanding 4.A	Interactions within biological systems lead to complex properties.
Essential Knowledge	4.A.6 Interactions among living organisms and with their environment results in the movement of matter and energy.
Science Practice	1.4 The student can use representations and models to analyze situations or solve problems qualitatively and quantitatively.
Learning Objective	4.15 The student is able to use visual representations to analyze situations or solve problems qualitatively to illustrate how interactions among living systems and with their environment result in the movement of matter and energy.

Link to Learning

Climate change can alter where organisms live, which can sometimes directly affect human health. Watch the PBS video “Feeling the Effects of Climate Change” in which researchers discover a pathogenic organism living far outside of its normal range.

Refer to [link]

The fungus Cryptococcus gattii has been known to cause a fatal illness. This fungus originally found in the tropics is now growing in parts of North America. What have scientists found out about this fungus?

The fungus was inadvertently introduced in North America by travelers
This fungus acquired pathogenic characteristics over time.
The disease was caused by contact with infected people
The fungus started growing more in colder climates as temperatures have risen due to global warming.

Levels of Ecological Study

When a discipline such as biology is studied, it is often helpful to subdivide it into smaller, related areas. For instance, cell biologists interested in cell signaling need to understand the chemistry of the signal molecules (which are usually proteins) as well as the result of cell signaling. Ecologists interested in the factors that influence the survival of an endangered species might use mathematical models to predict how current conservation efforts affect endangered organisms. To produce a sound set of management options, a conservation biologist needs to collect accurate data, including current population size, factors affecting reproduction (like physiology and behavior), habitat requirements (such as plants and soils), and potential human influences on the endangered population and its habitat (which might be derived through studies in sociology and urban ecology). Within the discipline of ecology, researchers work at four specific levels, sometimes discretely and sometimes with overlap: organism, population, community, and ecosystem (Figure 35.2).

A flow chart of three boxes shows the hierarchy of living organisms. The top box is labeled “Organisms, populations, and communities” and has a photograph of tall trees in a forest. The second box is labeled “ecosystems” and has a photograph of a body of water, behind which is a stand of tall grasses developing into more dense vegetation and trees as distance from the water increases. The third box is labeled “the biosphere” and shows a drawing of planet Earth.

Figure 35.2 Ecologists study within several biological levels of organization. (credit “organisms”: modification of work by "Crystl"/Flickr; credit “ecosystems”: modification of work by Tom Carlisle, US Fish and Wildlife Service Headquarters; credit “biosphere”: NASA)

Organismal Ecology

Researchers studying ecology at the organismal level are interested in the adaptations that enable individuals to live in specific habitats. These adaptations can be morphological, physiological, and behavioral. For instance, the Karner blue butterfly (Lycaeides melissa samuelis) (Figure 35.3) is considered a specialist because the females preferentially oviposit (that is, lay eggs) on wild lupine. This preferential adaptation means that the Karner blue butterfly is highly dependent on the presence of wild lupine plants for its continued survival.

Photo depicts a Karner blue butterfly, which has light blue wings with gold ovals and black dots around the edges.

Figure 35.3 The Karner blue butterfly (Lycaeides melissa samuelis) is a rare butterfly that lives only in open areas with few trees or shrubs, such as pine barrens and oak savannas. It can only lay its eggs on lupine plants. (credit: modification of work by J & K Hollingsworth, USFWS)

After hatching, the larval caterpillars emerge and spend four to six weeks feeding solely on wild lupine (Figure 35.4). The caterpillars pupate (undergo metamorphosis) and emerge as butterflies after about four weeks. The adult butterflies feed on the nectar of flowers of wild lupine and other plant species. A researcher interested in studying Karner blue butterflies at the organismal level might, in addition to asking questions about egg laying, ask questions about the butterflies’ preferred temperature (a physiological question) or the behavior of the caterpillars when they are at different larval stages (a behavioral question).

This photo depicts a wild lupine flower, which is long and thin with clam-shaped petals radiating out from the center. The bottom third of the flower is blue, the middle is pink and blue, and the top is green.

Figure 35.4 The wild lupine (Lupinus perennis) is the host plant for the Karner blue butterfly.

Population Ecology

A population is a group of interbreeding organisms that are members of the same species living in the same area at the same time. (Organisms that are all members of the same species are called conspecifics.) A population is identified, in part, by where it lives, and its area of population may have natural or artificial boundaries: natural boundaries might be rivers, mountains, or deserts, while examples of artificial boundaries include mowed grass, manmade structures, or roads. The study of population ecology focuses on the number of individuals in an area and how and why population size changes over time. Population ecologists are particularly interested in counting the Karner blue butterfly, for example, because it is classified as federally endangered. However, the distribution and density of this species is highly influenced by the distribution and abundance of wild lupine. Researchers might ask questions about the factors leading to the decline of wild lupine and how these affect Karner blue butterflies. For example, ecologists know that wild lupine thrives in open areas where trees and shrubs are largely absent. In natural settings, intermittent wildfires regularly remove trees and shrubs, helping to maintain the open areas that wild lupine requires. Mathematical models can be used to understand how wildfire suppression by humans has led to the decline of this important plant for the Karner blue butterfly.

Teacher Support

As humans continue to rise in population and the infrastructure to handle this population growth continues to expand, so do the boundaries between populations of animals. Animals that were once a single population are divided by structures such as highways. Many places are trying to remedy this ecosystem disruption by creating wildlife overpasses. One such overpass is being constructed in Seattle. For more information, read the Seattle Times article.

Community Ecology

A biological community consists of the different species within an area, typically a three-dimensional space, and the interactions within and among these species. Community ecologists are interested in the processes driving these interactions and their consequences. Questions about conspecific interactions often focus on competition among members of the same species for a limited resource. Ecologists also study interactions among various species; members of different species are called heterospecifics. Examples of heterospecific interactions include predation, parasitism, herbivory, competition, and pollination. These interactions can have regulating effects on population sizes and can impact ecological and evolutionary processes affecting diversity.

For example, Karner blue butterfly larvae form mutualistic relationships with ants. Mutualism is a form of a long-term relationship that has coevolved between two species and from which each species benefits. For mutualism to exist between individual organisms, each species must receive some benefit from the other as a consequence of the relationship. Researchers have shown that there is an increase in the probability of survival when Karner blue butterfly larvae (caterpillars) are tended by ants. This might be because the larvae spend less time in each life stage when tended by ants, which provides an advantage for the larvae. Meanwhile, the Karner blue butterfly larvae secrete a carbohydrate-rich substance that is an important energy source for the ants. Both the Karner blue larvae and the ants benefit from their interaction.

Ecosystem Ecology

Ecosystem ecology is an extension of organismal, population, and community ecology. The ecosystem is composed of all the biotic components (living things) in an area along with the abiotic components (non-living things) of that area. Some of the abiotic components include air, water, and soil. Ecosystem biologists ask questions about how nutrients and energy are stored and how they move among organisms and the surrounding atmosphere, soil, and water.

The Karner blue butterflies and the wild lupine live in an oak-pine barren habitat. This habitat is characterized by natural disturbance and nutrient-poor soils that are low in nitrogen. The availability of nutrients is an important factor in the distribution of the plants that live in this habitat. Researchers interested in ecosystem ecology could ask questions about the importance of limited resources and the movement of resources, such as nutrients, though the biotic and abiotic portions of the ecosystem.

Career Connection

Ecologist

A career in ecology contributes to many facets of human society. Understanding ecological issues can help society meet the basic human needs of food, shelter, and health care. Ecologists can conduct their research in the laboratory and outside in natural environments (Figure 35.5). These natural environments can be as close to home as the stream running through your campus or as far away as the hydrothermal vents at the bottom of the Pacific Ocean. Ecologists manage natural resources such as white-tailed deer populations (Odocoileus virginianus) for hunting or aspen (Populus spp.) timber stands for paper production. Ecologists also work as educators who teach children and adults at various institutions including universities, high schools, museums, and nature centers. Ecologists may also work in advisory positions assisting local, state, and federal policymakers to develop laws that are ecologically sound, or they may develop those policies and legislation themselves. To become an ecologist requires an undergraduate degree, usually in a natural science. The undergraduate degree is often followed by specialized training or an advanced degree, depending on the area of ecology selected. Ecologists should also have a broad background in the physical sciences, as well as a sound foundation in mathematics and statistics.

This photo shows a woman looking into a small cage with its door open. The cage sits on short prairie grass, next to a hole with dirt around the rim. In the background sits a second, closed cage.

Figure 35.5 This landscape ecologist is releasing a black-footed ferret into its native habitat as part of a study. (credit: USFWS Mountain Prairie Region, NPS)