Unit 8: Ecology

Ecology is all about the interactions that organisms have amongst themselves and with their environment. This can be seen on a small scale, within populations, and on larger scales, in ecosystems and across the globe. The relationships that exist between organisms are complex and ever changing. We are constantly responding to our environment and those around us. Some of the largest problems plaguing our planet right now are the largest culprits to the changing landscape of ecosystems across the globe. All of these issues come together in the awesome unit of Ecology.

Browse slides from the stream 'Nutrient Cycles & Succession.'

Browse slides from the stream 'Community Ecology,' where we cover topics including Ecology.

Browse slides from the stream 'Population Ecology.'

Organisms have highly evolved mechanisms of responding to their environment. These responses may be behavioral, such as finding higher ground during a rainstorm, or physiological, such as an increase in epinephrine during a high-stress situation. A number of environmental factors, such as changing temperature, weather patterns, an increase or decrease in food or water, or a decrease in a shelter can lead to changes within an organism. Many organisms are dependent on the seasons, hibernating or migrating in winter. These mechanisms and responses help them to survive and reproduce.

All organisms in an ecosystem need energy. Remember, all the energy that we have on earth originates from the sun. Photosynthetic bacteria convert this energy into usable energy through photosynthesis. Energy flows through ecosystems, starting with energy from the sun and traveling through photosynthetic organisms and the organisms that consume them. The majority of energy is lost in the form of heat between levels of the ecosystem. This is because energy is used by the individual in order to produce heat, digest, and go through basic daily functioning.

A population is defined as a group of the same species living in the same area. An example of this would be humans living in Chicago. Within a population, there are a number of factors that affect the health and growth of the species. 

Populations are often affected by factors that inhibit their ability to continue to survive and reproduce. These factors may be broken into two categories: density-dependent factors and density-independent factors.

A community refers to a group of different populations living in the same area. An example of this would be humans, dogs, and rats living in the city of Chicago. A community has many interactions between the populations of species that live there. These interactions can be positive, negative, or neutral. When studying a community, scientists often measure the species diversity and species composition in that area. This refers to the number of unique species living in the area and what percent of the population is represented by each species. A species with a large number of unique species with equally distributed populations would be considered highly diverse.

Biodiversity refers to the amount of diversity in species and within species in an ecosystem. Ecosystems with a higher level of biodiversity are better able to respond to changes in their environment. This is due to the increase in potential defenses to various problems. For example, if a highly diverse population is infected with a specific pathogen, it is likely that at least a few individuals within the population possess some sort of immunity or enhanced ability to fight the pathogen. This allows the population to survive through the challenging environmental shift. Less diverse ecosystems may collapse if exposed to extreme changes in the environment or other detrimental events. Using the previous example, it is less likely that individuals within a population would possess immunity to the pathogen, and it is more likely that the entire population may be wiped out from the pathogen. An increase in genetic diversity always leads to an increase in protection from environmental changes. This concept is tested frequently on the AP exam.

Disruptions to ecosystems may lead to the process of evolution, as changes in the environment may lead to a selective advantage for some species over others. This process takes place if certain adaptations give organisms an advantage over others to survive and reproduce.