Ecology

Ecosystems and Energy Flow

Ecology is the study of interactions among organisms and their environment. Understanding ecosystems and how energy flows through them is fundamental to biology.

• What is an ecosystem? An ecosystem is a community of living organisms (biotic factors) interacting with each other and with their non-living (abiotic) environment. Components include producers, consumers, decomposers, and abiotic factors such as sunlight, water, and minerals.

• Open vs. Closed Ecosystems: Most ecosystems are open systems, exchanging energy and matter with their surroundings. Closed systems are rare in nature.

• Biomes: A biome is a large ecological area with distinct climate, flora, and fauna. Examples in Minnesota include temperate forests and prairies.

• Energy Flow: Energy enters ecosystems via sunlight, captured by producers (plants) through photosynthesis. Energy is transferred through trophic levels (producers → primary consumers → secondary consumers → decomposers).

• Trophic Pyramid: The trophic pyramid illustrates energy loss at each trophic level. Typically, only about 10% of energy is transferred from one level to the next.

• Gross vs. Net Primary Productivity: Gross primary productivity (GPP) is the total energy captured by producers. Net primary productivity (NPP) is the energy remaining after producers' respiration, available to consumers.

• Biomass: Biomass is the total mass of living matter in a given area. It can be measured at different trophic levels or over time.

Example: In a Minnesota forest, sunlight is captured by trees (producers), which are eaten by deer (primary consumers), which may be preyed upon by wolves (secondary consumers).

Community Relationships

Communities are groups of interacting populations. Relationships among species shape community structure and function.

• Types of Inter-Specific Relationships:

  • Neutralism: No significant effect on either species.

  • Commensalism: One species benefits, the other is unaffected.

  • Mutualism: Both species benefit (e.g., bees pollinating flowers).

  • Parasitism: One species benefits at the expense of another (e.g., tapeworm in mammals).

  • Predator-Prey: One organism (predator) kills and eats another (prey).

  • Competition: Both species are harmed by the interaction as they vie for the same resource.

Example: Wolves and coyotes may compete for similar prey in overlapping territories.

Additional info: Competition is considered a lose-lose relationship because both species expend energy and resources, reducing their fitness.

Population Ecology

Population ecology examines how and why populations change over time and space.

• Logistic Growth: Populations often grow rapidly at first, then slow as resources become limited, following the logistic growth model:

• Carrying Capacity (K): The maximum population size an environment can sustain.

• Exponential Growth: Occurs when resources are unlimited. Population increases by a constant proportion:

• Factors Affecting Growth: Resource availability, predation, disease, and competition.

• Life History Strategies: Species may be r-selected (many offspring, little care) or K-selected (few offspring, more care).

• Survivorship Curves: Graphs showing the proportion of individuals surviving at each age. Three types:

  • Type I: High survival early, drops with age (e.g., humans).

  • Type II: Constant death rate (e.g., birds).

  • Type III: High mortality early, survivors live long (e.g., many fish).

Example: Deer populations may grow rapidly after a mild winter, then stabilize as food becomes scarce.

Assessing Biodiversity of Ecosystems

Sampling and Data Collection

Biodiversity assessment involves systematic sampling and data analysis to understand species diversity and ecosystem health.

• Sampling Quadrats: A quadrat is a defined area used to sample organisms. Procedures include random placement and consistent measurement.

• Data Aggregation: Individual quadrat data are combined to estimate overall biodiversity.

Biodiversity Indices

• Simpson Index (D): Measures the probability that two individuals randomly selected from a sample belong to the same species. Formula: where is the proportion of individuals in the th species, and is the total number of species.

• Shannon-Wiener Index (H): Measures species diversity, accounting for abundance and evenness. Formula:

• Species Richness: The total number of different species present in an ecosystem.

Example: Comparing indices from two woodlands can reveal which is more diverse or evenly populated.

Tree Species Identification

• Major Native Tree Species: Recognizing species such as Quercus rubra (red oak), Acer saccharum (sugar maple), Tilia americana (American basswood), and Celtis occidentalis (hackberry) is important for ecological studies.

• Tree Population Structure: Comparing tree populations between different sites can indicate ecological differences or impacts.

Summary Table: Types of Species Interactions

Additional info: The table above summarizes the main types of interspecific relationships found in ecological communities.