Population and Community Ecology

Chapter 34: Population and Community Ecology

34.1 The Scope of Ecology

• Definition of Ecology: Ecology is the study of the interactions of organisms with each other and with their physical environment.

• Key Questions:

  • How are organisms adapted to their environment?

  • How do these adaptations affect their interactions with other organisms?

• Population: All organisms belonging to the same species within an area at the same time.

• Community: All the various populations at a particular location.

• Ecosystem: An ecosystem encompasses a community of populations as well as the nonliving environment.

  • Example: Energy flow and chemical cycling can affect the success of populations within an ecosystem.

• Biosphere: The portion of Earth where living organisms exist.

34.2 Patterns of Population Growth

• Population Growth: Each population has a particular pattern of growth influenced by the growth rate (r).

  • Example: If a population has 1,000 members with a birth rate of 30/year and a death rate of 10/year, the growth rate per year is calculated as:
    (30 - 10) / 1000 = 0.02 = 2.0\% \text{ per year}
    (Note: This does not include immigration and emigration)

• Biotic Potential: The highest possible rate of natural increase for a population, influenced by limiting factors including:

  • Number of offspring that survive to reproductive age.

  • Competition for resources.

  • Age distribution within the population.

  • Presence of predators and diseases.

• Growth Phases:

  • Exponential Growth: Results in a J-shaped curve with two phases:

  • Lag Phase: Slow growth due to small population.

  • Exponential Growth Phase: Growth accelerates as population reaches biotic potential.

• Environmental Resistance: Encompasses those environmental conditions that prevent populations from reaching their biotic potential:

  • Limited food supply

  • Accumulation of waste

  • Increased competition

  • Predation

• Logistic Growth: Occurs when environmental resistance increases and population growth levels off; represented by an S-shaped curve with four phases:

  • Lag Phase

  • Exponential growth phase

  • Logistic growth phase: Growth slows down as the population reaches carrying capacity.

  • Stable Equilibrium Phase: Little or no growth occurs as births equal deaths.

• Carrying Capacity (K): The maximum number of individuals of a species that an environment can support.

34.3 Interactions Between Populations

• Life History Patterns: Characterized by the time to reach reproductive maturity and level of reproductive output.

  • Opportunistic Pattern (r-strategists):

  • Characteristics: Small size, early maturity, short life span, many small offspring with little or no parental care.

  • Examples: Weeds and insects.

  • Equilibrium Pattern (K-strategists):

  • Characteristics: Larger size, slow maturity, longer life spans, fewer offspring with invested energy in growth and survival of offspring.

  • Examples: Birds and mammals.

• Population Control Factors:

  • Density-independent factors: Abiotic factors (e.g., weather, natural disasters) affect all population sizes equally.

  • Density-dependent factors: Biotic factors (e.g., competition) whose effects depend on the population size.

• Competition: Occurs when members of two different species utilize the same limited resource, categorized by

  • Competitive Exclusion Principle: States that no two species can occupy the same niche simultaneously if resources are limited, causing one species to outcompete the other.

  • Resource Partitioning: The division of feeding niches that decreases competition and allows species to coexist in different habitats.

• Examples of Competition:

  • Paramecium Competition: P. aurelia outcompetes P. caudatum when grown together.

  • Barnacle Competition: Balanus barnacles outcompete Chthamalus barnacles at lower depths.

  • Intraspecific Competition: More intense competition within a species due to similar resource requirements.

  • Invasive Species: Non-native species that often outcompete local species.

34.4 Ecological Succession

• Ecological Succession: A directional change in a community’s composition involving extinction and colonization.

  • Primary Succession: Establishment of a plant community in an area lacking soil formation.

  • Secondary Succession: The recovery of a community to its natural vegetation after a disturbance.

  • Pioneer Species: The first species to initiate secondary succession.

• Models of Succession:

  • Climax-Pattern Model: Suggests specific areas lead to a predictable climax community.

  • Facilitation Model: Each successive community prepares for the next.

  • Inhibition Model: Colonizing species hold space until they die.

  • Tolerance Model: Different plant types can colonize simultaneously, determined by chance.

Chapter 35: Nature of Ecosystems

35.1 The Biotic Components of Ecosystems

• Ecosystems: Comprised of both abiotic (nonliving) and biotic (living) components.

• Abiotic Components: Include sunlight, inorganic nutrients, soil type, water, temperature, and wind.

• Biotic Components: Various populations of species that form a community.

35.2 Energy Flow and Chemical Cycling

• Energy Flow: Involves the flow of energy as it moves from producers to consumers. Chemical cycling involves recycling of nutrients.

• Producers: Autotrophs that produce organic nutrients from inorganic sources (e.g., green plants, algae).

• Heterotrophs: Require an external organic source, categorized as:

  • Herbivores: Primary consumers that feed on plants or algae.

  • Carnivores: Secondary consumers (feed on herbivores) and tertiary consumers (feed on other carnivores).

  • Omnivores: Feed on both plants and animals.

• Decomposers: Break down nonliving organic matter to release inorganic nutrients back to the environment.

  • Detritivores: Organisms that feed on decomposing organic matter.

• Energy Loss: Generally, only about 10% of energy is transferred to the next trophic level, explained through ecological pyramids.

• Trophic Levels: Hierarchical levels in an ecosystem, such as primary producers, primary consumers, secondary consumers.

35.3 Global Biogeochemical Cycles

• Biogeochemical Cycles: Pathways involving biotic and geological components for recycling of essential elements in ecosystems.

  • Reservoir: Sources unavailable to producers (e.g., fossil fuels).

  • Exchange Pool: Where organisms obtain chemicals (e.g., atmosphere).

• Types of Biogeochemical Cycles:

  • Gaseous Cycle: Involves elements returning to the atmosphere (e.g., carbon, nitrogen cycles).

  • Sedimentary Cycle: Involves elements sourced from soil, returned by decomposers (e.g., phosphorus cycle).

• The Water Cycle: Involves evaporation, condensation, and precipitation processes, including transpiration from plants.

• The Carbon Cycle: Plants uptake CO2 through photosynthesis, which is returned to the atmosphere through respiration.

• Human Impact: Human activities increase atmospheric CO2 via deforestation and fossil fuel combustion, contributing to climate change.

35.4 Consequences of Climate Change

• Climate Changes: Historically occurred through natural variations; current changes are rapid and anthropogenic.

• Contributors of Climate Change:

  • Greenhouse Effect: Various gases contributing to warming.

  • Deforestation: Alters carbon storage capacity and climate.

• Consequences:

  • Increased rainfall variability leading to droughts and floods.

  • Arctic ice melting leading to rising sea levels that threaten coastal communities.

  • The responsibility of individuals in mitigating climate change through resource conservation practices.