Ecology and Biodiversity: Key Concepts and Case Studies

Levels of Organization

The hierarchical scale ecologists use to study life, from largest to smallest: Biosphere → Biome → Ecosystem → Community → Population → Species → Organs → Tissues → Cells → Organelles → Molecules → Atoms.

Biosphere

The entire Earth and every living thing on it (land, water, air). Made up of the atmosphere (air), hydrosphere (water), and lithosphere (land).

Taxonomy

The formal classification of organisms into groups based on similarities/differences.

The Five Kingdoms

Monera (bacteria, unicellular, no nucleus), Fungi (mushrooms/yeasts/molds), Plantae (photosynthetic producers), Animalia (heterotrophic consumers), Protista (catch-all eukaryotes that aren't plant/animal/fungus, e.g., amoebas).

Binomial Nomenclature

The two-name system for naming species: Genus (capitalized) + species (lowercase), e.g., Homo sapiens.

Hybrid

Offspring of two different species within the same genus that are typically sterile.

Ecosystem

A community of organisms interacting with each other and their physical (abiotic) environment.

Abiotic Components

Non-living parts of an ecosystem: sunlight, climate (temperature, rainfall/humidity), soil (sand/silt/clay, minerals), and water (flowing/still, salt/fresh, pH).

Biotic Components

Living parts of an ecosystem, divided into three trophic levels: Producers, Consumers, and Decomposers.

Producers

Organisms that use the sun's energy to make their own food via photosynthesis.

Consumers

Organisms that must eat other organisms to get energy, divided into primary, secondary, tertiary, and quaternary consumers.

Decomposers

Insects, microorganisms, bacteria, and fungi that break down dead producers/consumers into nutrients.

Photosynthesis

CO₂ + Water (+ sunlight + chlorophyll) → Glucose + Oxygen.

Energy Pyramid

Shows energy transfer from the sun → producers → primary consumers → secondary consumers, up the food chain.

Homeostasis (Dynamic Equilibrium)

A self-regulating process where ecosystems maintain stability while adjusting to change.

Three Mechanisms of Homeostasis

Species Interactions, Feedback Loops, and Ecological Succession.

Negative Feedback Loop

A process that counteracts/stabilizes change.

Positive Feedback Loop

A process that amplifies change, causing a runaway effect.

Ecological Succession

The gradual process by which an ecosystem returns to equilibrium after a disturbance.

Biodiversity

The variety and abundance of living things in an ecosystem.

Why Biodiversity Matters

A healthy, biodiverse ecosystem provides essential ecosystem services.

Redundancy

When multiple species perform similar roles in an ecosystem.

Resilience

An ecosystem's ability to withstand, adapt to, and recover from a stress event.

Keystone Species

A species on which many other species in an ecosystem depend.

Trophic Cascade

An ecological phenomenon triggered by adding or removing a top predator.

Carrying Capacity (K)

The maximum population size an environment can sustainably support long-term.

Population Oscillation Around K

A typical population oscillates slightly around carrying capacity.

Tipping Point

The point at which a population overshoots carrying capacity so severely that it triggers a collapse, rather than a gentle oscillation back to K.

Case Study: Kaibab Plateau Mule Deer

On Arizona's Kaibab Plateau, predators were exterminated to protect the deer herd, leading to an explosion in deer population and a subsequent crash when carrying capacity was exceeded.

Bioindicator Species

Species especially sensitive to a pollutant or environmental stressor, used to infer the presence and concentration of pollutants.

Genetic Diversity

Differences in DNA among individuals within a species, with higher genetic diversity leading to higher fitness/adaptability.

Fitness

An organism's ability to adapt, survive, and reproduce.

Inbreeding vs. Outbreeding

Inbreeding decreases genetic diversity and fitness, while outbreeding maintains or increases genetic diversity.

Species Diversity

The variety and relative abundance of different species in an ecosystem.

Three Factors Affecting Species Diversity

(1) Structural complexity of the ecosystem, (2) Latitudinal gradient, (3) Species interactions.

Structural Complexity

The more habitats/layers/hiding spots an ecosystem has, the more species it can support.

Latitudinal Gradient

Biodiversity generally increases moving from the poles toward the equator.

Species Interactions

How species sharing an ecosystem interact, mainly through predator/prey relationships and competition for resources.

Ecosystem Diversity

The broadscale diversity of different habitats within one ecosystem.

HIPPOC

Mnemonic for the six major threats to biodiversity: Habitat Loss, Invasive Species, Pollution, Patterns of Disturbance, Overharvesting, Climate Change.

Habitat Conversion

Converting one type of habitat into another, which may threaten species adapted to the original habitat.

Habitat Fragmentation

Cutting a habitat into smaller, disconnected pieces, leading to smaller gene pools and reduced fitness.

Invasive Species

Non-native species introduced to a new area that outcompete native species and disrupt the food web.

Pollution

Toxic substances in the environment that can eliminate species from an area.

Altered Patterns of Disturbance

Some ecosystems need regular natural disturbances to stay healthy.

Overharvesting

Harvesting a species excessively, upsetting the food web.

Poaching

The illegal taking of wildlife, a subtype of overharvesting.

Limiting Factors

Conditions that restrict a species' population size/range.

Tolerance Limits

The range of conditions under which an organism can survive.

Climate Change (as a Biodiversity Threat)

Shifts limiting factors outside a species' tolerance range, forcing organisms to adapt, relocate, or go extinct.

Endemic Species

A species that exists naturally in only one specific geographic area.

Biodiversity Hotspot

An area with both an unusually high number of endemic species and an unusually high human threat to biodiversity.

Galapagos Islands Case Study

An island group isolated for ~9 million years, leading to the evolution of many endemic species.

NEPA

Process law requiring federal projects to study environmental impact and allow public comment.

ESA (1973)

Protects threatened/endangered species and their habitat.

ESA 'Taking'

Illegal to harass, harm, hunt, kill, capture, or trade a listed species.

Snail Darter vs. TVA

First ESA case to reach the Supreme Court regarding an endangered fish and dam construction.

Bald Eagle

Nearly extinct due to habitat loss and DDT; listed endangered in 1978 and delisted in 2007 after recovery.

IUCN Red List

Global version of the Endangered Species List with various categories of species status.

Rewilding (3 Cs)

Cores, Corridors, and Carnivores to enhance biodiversity.

Cores

Large protected areas that support more biodiversity.

Corridors

Link cores together to enhance genetic/species diversity.

Carnivores

Apex predators that are keystone species; losing them can cause trophic cascades.

Habitat Encroachment

Humans invading undisturbed habitat, leading to less wildlife space.

Spillover Event

A disease jumps from animal to human.

Biodiversity ↔ Pandemics

Losing biodiversity increases the risk of disease spillover to humans.