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Unit 2

2.0 Intro to Unit 2

4 min readjune 3, 2021

jenni520065

Jenni MacLean


AP Environmental Science ♻️

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2.0 Intro to Unit 2

Unit 1 was a really in-depth look into the foundational cycles and processes that drive biological processes. Now with unit 2, we will begin to look at how organisms interact with their environment and what that means for humans! 

Biodiversity 

Biodiversity is the variety of life in a given location or ecosystem. This measurement can be further broken down and calculated mathematically to rate an area for its ecological relevance. This is important because we can make smart choices about what locations we should develop into condos and where we should designate a wildlife refuge.
Genetic diversity is the total number of different alleles (variations of a gene ex: red hair, long neck, etc.) in a population that would allow for different potential phenotypes (physical features). A genetically diverse population has a much higher chance of surviving environmental pressures like disease or climate change. Species diversity is the total number of different species in a given area. This can be plants or animals, depending on what is being studied. The same concept applies here–the more variation in an ecosystem’s species, the greater chance that one will survive if there is a disaster or massive change to the environment. 
The number of different species in an ecosystem is measured as species richness, and the comparative number of each species to the next is the species evenness. I promise it’s not as confusing as it seems! Let’s look at an example: 
A savanna has lions, giraffes, and zebras. The species richness would be 3 because there are 3 total species.  
If there are 100 total animals, and there are 98 zebra, 1 lion, and 1 giraffe, the species evenness would be very low.  
If there are 100 total animals, and there are 40 zebra, 40 giraffe, and 20 lions, the evenness would be much higher.  
Ecologists use these numbers to calculate the health of an ecosystem in a number called Shannon’s Index
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Ecosystem Services

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Ecosystem services are anything that humans benefit from the natural world. They can be broken down into four major categories. 
  • Provisioning: Products that are provided.
    • Example: Wood from forest and food from animals.
  • Regulating: Maintain processes.
    • Example: Climate regulation by cycling CO2.
  • Cultural: Nonmaterial benefits.
    • Example: Recreation or emotional–enjoying a view. 
  • Supporting: Allow for other services to exist.
    • Example: Nutrient cycling and primary production. 
Humans rely on ecosystem services. Without natural processes like decomposition and honey bees pollinating fruiting plants, we would not be able to survive. 

Ecological Tolerance  

Any individual or species has a range of conditions (temperature, available water, food, etc.) that it can tolerate before it dies. This is its ecological tolerance. Resistance is the ability of an ecosystem or a species to survive a disturbance, while resilience is the ability to bounce back after experiencing a disturbance. In general, genetically diverse, generalist populations tend to have a higher tolerance for change.  So a species like grass 🌿 can bounce back quickly after a fire, while a species like a panda 🐼 can’t repopulate or survive if their forest is cut down. Information like this helps scientists decide what species might be more vulnerable to extinction. 

Natural Disruptions to Ecosystems 

The Earth is constantly changing under natural long-term cycles that drastically alter environments, as well as experiencing sudden catastrophic events. These disruptions can have as much of an ecological impact as man-made or anthropogenic changes. Some of these changes include natural climate change and geologic processes. Natural climate change is a slow process due to naturally changing levels of greenhouse gases caused by changes in metabolic processes and volcanic eruptions. By metabolic processes, we mean the evolution of photosynthesis and how plants and bacteria pulled massive amounts of carbon out of the atmosphere. Tectonic movement causes large upheavals of land and changes the environment geologically and by creating microclimates. 

Ecological Succession

When the environment experiences changes or disasters (man-made or natural), it will inevitably recover and likely follow some predictable patterns. This pattern is known as ecological succession and looks at how ecosystems tend to heal with pioneer species like lichens and then grow more extensive and more established plant species over time. Let's take a look at what makes the two types of succession different. 
Primary Succession:  Starts with no soil.
This is caused by a complete disruption of the ecosystem–something like a volcanic eruption or geologic change that leaves only bedrock exposed. Humans create primary succession by paving land. Think of how long it would take an abandoned parking lot to turn back into a forest! 
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Secondary Succession: Starts with soil
Secondary succession events are much more likely. This can occur naturally after a fire or flood and anthropogenic events like clearcutting. The important difference is that the soil is intact! A lot of plants are adapted to survive these events. Grass is a great example–the majority of the plant lives underground and can quickly send up new leaves.  
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