AP Environmental Science Unit 2 Review (Everything you Need to Know!)

Mr. Smeads introduces Unit 2 of the AP Environmental Science course, emphasizing the importance of biodiversity. He highlights that understanding the three levels of biodiversity – genetic, species, and ecosystem – is crucial. Genetic diversity refers to the variance of genes within a population, increasing adaptability to disturbances. Species diversity involves both species richness (number of different species) and species evenness (distribution of population sizes). Ecosystem biodiversity relates to the variety of ecosystems in a given area. All three levels are beneficial for ecosystem resilience and stability.

Ecosystem services are the financial benefits humans derive from natural ecosystems, categorized into four types. Provisioning services are direct products like wood. Supporting services are ecosystem processes that aid human activities, such as pollination for agriculture. Regulating services stabilize climate and environmental factors, like carbon sequestration by trees, saving money from disaster mitigation. Cultural services provide recreational and intellectual benefits, generating revenue from tourism or scientific research. Disruptions to these services, such as oil spills, can have significant economic and environmental consequences.

The theory of Island Biogeography explains species richness on islands based on two rules. Islands closer to the mainland tend to have higher species richness due to easier migration. Larger islands also have higher species richness because they offer greater habitat diversity. Island ecosystems often lead to specialized species with narrow food and habitat choices, making them vulnerable to invasive species, as exemplified by the dodo bird.

Ecological tolerance defines the range of conditions an organism or species can withstand before harm or death. Organisms have an optimal range for survival, growth, and development. Moving outside this range leads to a zone of physiological stress and eventually a zone of intolerance, resulting in death. Genetic diversity within a population allows some individuals to have wider tolerance ranges, helping the species adapt to environmental changes over time.

Ecosystems face natural disturbances, categorized by frequency: periodic (e.g., rainy seasons), episodic (e.g., hurricanes, forest fires), and random (e.g., asteroid strikes). Earth's climate also changes gradually over tens of thousands of years due to Milankovitch Cycles, which alter Earth's orbit and tilt. These slow changes influence global temperature and sea levels, impacting coastal and marine ecosystems. Species adapt to these changes; adaptations are genetic mutations that increase an organism's survival and reproductive success, as illustrated by the evolution of opposable thumbs in early hominids.

Ecological succession describes how ecosystems change over time. Primary succession occurs on bare rock, starting with pioneer species like moss and lichen, which form shallow soil. This allows for the succession of grasses, shrubs, and eventually shade-intolerant and then shade-tolerant trees, leading to a climax community with high biomass and species richness. Secondary succession follows a similar pattern but begins on existing soil after a disturbance (e.g., forest fire, abandoned agricultural field). Keystone species are vital to their ecosystems; their removal can cause entire ecosystem collapse, as seen with wolves impacting deer populations or beavers creating unique habitats.