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Topics in Depth

Population Growth

To understand and appreciate ecology at the community and ecosystem levels, you must first have a good grasp on ecology at the population level, often called population ecology. Population ecology...

Growth Rate

Ecologists do not simply measure the absolute growth of a population. Doing this would yield a silly, incoherent number. Think about it. What would you make of the statement "The population of peng...

Maximum Sustainable Yield (MSY)

Before moving onto other population characteristics that are of interest to ecologists, let’s briefly look at how the principles of population growth we just discussed (see previous topic for a r...

Reproductive and Survivorship Strategies

It may come as no surprise to you that different organisms have different strategies for reproduction. And we are not talking about a nifty array of cheesy pickup lines. At one extreme, some organi...

Age Structure

Another characteristic of populations that ecologists measure is population age structure. This characteristic is as simple as it sounds: it’s a summary of the number of individuals of each age i...

Species Interactions

With a solid population perspective under your belt, you are officially ready to take ecology to the next level. Literally. In this section, we will explore community ecology, the study of how popu...

Competition

The first species interaction we will tackle is competition, a word you are likely familiar with. But, as usual, in ecology, competition has a specific meaning. Why can't we all just get along?Comp...

Predation

We suspect that if you were to ask your grandma to name a species interaction, she would say "Eh? Come again? What did you say?" But then, she would probably say "Predation." Right? Our grandma wou...

Symbiosis

The final species interaction we will discuss is symbiosis, or the interaction where two species live in the same location, and one or both receive a benefit from the other. Under this definition,...

Community Succession

Competition, predation, and symbiosis are especially important in structuring a community as it recovers from major disruptions. These disruptions are often the same things we explored as density-i...

Ecosystem Habitats

Congratulations! You have now advanced to the third and final level of ecology, where we will explore the interactions between communities and their physical and chemical environments. In this sect...

Ecosystem Energy Flow

Nearly all of the energy that drives ecosystems ultimately comes from the sun. Solar energy, which is an abiotic factor, by the way, enters the ecosystem through the process of photosynthesis. You...

The Water Cycle

In the previous section, you learned how the community portion of an ecosystem interacts with energy, an essential abiotic factor in the habitat. In these next sections, we will look at how communi...

The Carbon Cycle

Carbon is likely the next most important chemical in an ecosystem. Most of the carbon on Earth is found in the atmosphere in the form of carbon dioxide, or CO2. Plants and other producers extr...

The Nitrogen Cycle

Even though organisms use nitrogen less than they do carbon or water, it could also be said that a lack of nitrogen would eradicate life on Earth. As with carbon, most of the nitrogen in the world...

The Phosphorus Cycle

The last important chemical in an ecosystem that we will tackle in this unit is phosphorous. This essential chemical is used by organisms as one of the main components of DNA. Nitrogen and carbon a...

Test Your Knowledge!

Population Ecology QuestionsA penguin population has 10,000 individuals. If 1,000 chicks were born and 2,000 penguins died in a year, what would the birth rate be? The death rate? The growth rate?...

Common Mistakes

Population EcologyExponential vs. Logistic Growth. Perhaps you’re still trying to figure out the difference between exponential growth and logistic growth. The best way to understand these differ...

Made from Trees

Offline ResourcesHuman Ecology: Basic Concepts for Sustainable Development. By Gerald G. Marten. Published by Earthscan in 2001.Population Ecology: A Unified Study of Animals and Plants. By Michae...

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