Ecosystem Ecology and Biodiversity: Study Guide for Exam 3

Ecosystem Ecology and Biodiversity

Overview

This study guide covers key concepts in ecosystem ecology, energy flow, biogeochemical cycles, biodiversity, and conservation biology. Understanding these topics is essential for analyzing how living organisms interact with their environment and the importance of preserving biodiversity.

Ecology of Ecosystems

Eutrophication

• Definition: Eutrophication is the process by which a body of water becomes overly enriched with nutrients, often leading to excessive growth of algae and depletion of oxygen.

• Direct Causes: Runoff containing fertilizers, sewage, or animal waste introduces high levels of nitrogen and phosphorus into aquatic systems.

• Effects: Algal blooms, decreased oxygen levels (hypoxia), fish kills, and loss of biodiversity.

• Example: The "dead zone" in the Gulf of Mexico is caused by nutrient runoff from the Mississippi River.

Biological Macromolecules and Nitrogen

• Macromolecules with Nitrogen: Proteins and nucleic acids contain nitrogen groups.

• Macromolecules without Nitrogen: Carbohydrates and lipids do not contain nitrogen.

• Example: Amino acids (building blocks of proteins) have amino groups containing nitrogen.

Nitrogen Fixation

• Definition: Nitrogen fixation is the process where bacteria convert atmospheric nitrogen (N2) into ammonia (NH3), a form usable by plants.

• Key Organisms: Nitrogen-fixing bacteria such as Rhizobium and cyanobacteria.

Energy Flow Through Ecosystems

• Energy Transfer: Approximately 10% of energy is transferred from one trophic level to the next; the rest is lost as heat, waste, or used for metabolism.

• Reason for Energy Loss: Energy is lost due to respiration, movement, and heat dissipation.

• Trophic Energy Calculations: If a trophic level has 1000 kcal, the next level receives about 100 kcal.

Trophic Cascades and Top Predators

• Trophic Cascade: A process where changes at the top of the food web (e.g., removal of a top predator) cause ripple effects through lower trophic levels.

• Effects of Removing Top Predators: Can lead to overpopulation of herbivores and depletion of producers.

• Example: Removal of wolves from Yellowstone led to increased elk populations and decreased vegetation.

Role of Decomposers

• Definition: Decomposers (bacteria, fungi) break down dead organic matter, recycling nutrients back into the ecosystem.

• Importance: Essential for nutrient cycling and soil fertility.

Biogeochemical Cycles

Carbon Cycle

• Long-term Storage: Carbon is stored in fossil fuels, sedimentary rocks, and the deep ocean.

• Return to Atmosphere: Through respiration, combustion, and decomposition.

Nutrient Reservoirs in the Atmosphere

• Commonly Atmospheric: Carbon (as CO2), nitrogen (as N2), and oxygen (as O2).

• Not Atmospheric: Phosphorus is not commonly found in the atmosphere; it cycles mainly through rocks and soil.

Biodiversity and Conservation

Invasive Species

• Effects: Outcompete native species, disrupt food webs, and alter habitats.

• Success Factors: Lack of natural predators, rapid reproduction, and adaptability.

• Management Challenges: Prevention is more effective than removal; eradication is difficult once established.

Habitat Fragmentation

• Definition: The breaking up of continuous habitats into smaller, isolated patches.

• Consequences: Reduced gene flow, increased edge effects, and higher extinction risk for small populations.

Risks to Small, Isolated Populations

• Risks: Inbreeding, genetic drift, and reduced adaptability.

• Contrast: Large populations with high gene flow maintain greater genetic diversity and resilience.

Wildlife Corridors

• Definition: Strips of habitat that connect isolated populations, allowing movement and gene flow.

• Purpose: Reduce the negative effects of fragmentation and support biodiversity.

Climate Change and Biodiversity

• Effects: Alters habitats, shifts species ranges, and increases extinction risk.

• Species Movement: Species with greater dispersal ability are more likely to survive climate change by relocating to suitable habitats.

Biomagnification

• Definition: The increasing concentration of toxic substances in organisms at higher trophic levels.

• Example: Mercury and DDT accumulate in top predators.

Biodiversity Hotspots

• Definition: Regions with exceptionally high levels of species richness and endemism that are under threat from human activities.

Keystone Species

• Definition: A species with a disproportionately large effect on its ecosystem relative to its abundance.

• Example: Sea otters maintain kelp forest ecosystems by controlling sea urchin populations.

Ecosystem Services

• Definition: Benefits provided by ecosystems to humans, including provisioning (food, water), regulating (climate, disease), supporting (nutrient cycles), and cultural services.

Deforestation and Reforestation

• Deforestation: Leads to habitat loss, reduced biodiversity, and altered climate regulation.

• Reforestation: Restores habitats, increases biodiversity, and improves ecosystem services.

Captive Breeding Programs

• Purpose: To increase population sizes of endangered species and reintroduce them into the wild.

• Challenges: Maintaining genetic diversity and ensuring survival after release.

Genetic Bottlenecks

• Definition: A sharp reduction in population size leading to loss of genetic diversity.

• Effects: Increased vulnerability to disease and reduced adaptability.

Scientific Method and Experimental Design

Steps of the Scientific Method

• Observation: Gathering data about phenomena.

• Question: Formulating a question based on observations.

• Hypothesis: A testable explanation for an observation.

• Prediction: A specific, testable outcome expected if the hypothesis is correct.

• Experiment: Testing the prediction through controlled investigation.

• Analysis: Interpreting data to support or refute the hypothesis.

Hypothesis vs. Prediction

• Hypothesis: A general explanation (e.g., "Plants grow faster with more sunlight.")

• Prediction: A specific expected result (e.g., "If plants are given more sunlight, then they will grow 10 cm taller in two weeks.")

Variables in Experiments

• Independent Variable: The factor that is changed or manipulated by the researcher.

• Dependent Variable: The factor that is measured or observed in response to changes in the independent variable.

Summary Table: Key Concepts

Concept	Definition	Example/Notes
Eutrophication	Excess nutrient enrichment in water bodies	Algal blooms, fish kills
Nitrogen Fixation	Conversion of N2 to NH3 by bacteria	Rhizobium in legumes
Trophic Cascade	Ripple effects from changes in top predators	Wolves in Yellowstone
Biomagnification	Increase in toxin concentration up food chain	Mercury in fish
Keystone Species	Species with large ecosystem impact	Sea otters
Biodiversity Hotspot	Area with high species richness under threat	Tropical rainforests

Key Equations

• Energy Transfer Between Trophic Levels:

$E_{n} = E_{0} \times (0.1)^{n}$

• Where $E_{n}$ is the energy at trophic level n, $E_{0}$ is the energy at the producer level, and 0.1 represents 10% energy transfer efficiency.

Additional info: This guide integrates foundational concepts from ecosystem ecology and conservation biology, as outlined in Biology 2e Chapters 45-47, and provides context for exam preparation.