Ecology Review Notes

Food Web and Energy Flow

• Food Web: A complex network of feeding relationships among various organisms in an ecosystem.
• Energy Flow: Direction of energy transfer from one trophic level to another in a food web, typically from producers to various levels of consumers.

Communication in Species

• Effect of Communication: Organisms use various forms of communication (visual, auditory, chemical) to convey information, facilitating vital interactions such as mating, foraging, and territory establishment.
• Plant Communication: Research suggests plants can communicate under stress conditions (e.g., drought), influencing their and neighboring plant behaviors.

Density Dependent Factors

• Definition: Factors that affect population growth based on population density.
• Examples: Competition for resources, predation, disease, territoriality.
• Impact on Populations: As population density increases, resources become limited, leading to increased mortality or decreased reproduction.

Density Independent Factors

• Definition: Factors that affect population sizes regardless of the population's density.
• Examples: Natural disasters (floods, wildfires), climate, seasonal changes.
• Impact on Populations: Can lead to dramatic decreases in population size without regard to the current density.

Species Diversity Calculation

• Species Diversity: Refers to the variety and abundance of species within an ecosystem.
• Calculating Diversity: Use indices such as Simpson's Diversity Index to quantify biodiversity based on species richness and relative abundance.

Species-Species Interactions

• Predator-Prey: Dynamics where one species (predator) feeds on another (prey).
• Competitor-Competitor: Involves two or more species competing for the same resources (food, space).
• Mutualism: Both species benefit from the interaction (e.g., pollination).
• Parasitism: One organism (parasite) benefits at the expense of the other (host).
• Commensalism: One organism benefits while the other is neither helped nor harmed.

Responses to Environment

Behavioral and Physiological Mechanisms

• Responses: Organisms react to environmental changes through behavioral and physiological adaptations (e.g., hibernation, migration).
• Photoperiodism in Plants: Plants respond to changes in day length affecting their flowering time. Adaptation allows survival and reproductive success.

Examples of Responses

• Taxis and Kinesis: Movements toward or away from stimuli (e.g., light or chemicals in animals).
• Fight-or-Flight Response: Instantaneous physiological changes in response to threats.

Energy Flow in Ecosystems

Autotrophs and Heterotrophs

• Autotrophs: Organisms that produce their own energy (e.g., plants through photosynthesis).
• Heterotrophs: Organisms that obtain energy by consuming other organisms.

Energy Pyramid

• Producers (100%) → Primary Consumers (10%) → Secondary Consumers (1%) → Tertiary Consumers (0.1%).
• Role of Decomposers: Important for recycling nutrients in ecosystems, breaking down dead organic material.

Population Dynamics

Factors Influencing Population Growth

• Birth and Death Rates: Calculate using the formula:
  \text{Change in population size} = \text{Births} - \text{Deaths}.
• Logistic Growth Model: Models population growth that accounts for carrying capacity (K):
  \text{dN} = rN\left(\frac{K-N}{K}\right).

Limiting Factors

• Density-Dependent Factors: Affect growth as population density increases (e.g., food shortages leading to increased death rates).
• Density-Independent Factors: Affect populations irrespective of density (e.g., climate, natural disasters).

Community and Ecosystem Ecology

Community Structure

• Species Composition: A measure of the different species in a community and their relative abundance.
• Interactions: Including predator-prey dynamics and symbiotic relationships determine community structures and ecosystems' responses to changes.
• Biodiversity Impact: Higher biodiversity often leads to greater ecosystem resilience against disturbances and invasions.

Biodiversity and Its Importance

• Keystone Species: Have a disproportionately large effect on their environments; their loss can lead to ecosystem collapse.
• Impacts of Invasive Species: They can disrupt local ecosystems and outcompete native species, leading to declines in biodiversity.