8.1

Introduction to Ecology

  • Ecology is the scientific study of the interactions between organisms and their environment.

Importance of Ecology

  • The interactions between organisms and their environments affect the distribution and abundance of species.

  • Limiting factors influence species distribution.

Components of the Environment

  • Abiotic factors: Non-living chemical and physical components, such as:

    • Temperature

    • Light

    • Water

    • Nutrients

  • Biotic factors: Living components, including:

    • Competitors

    • Prey

    • Predators

Community Ecology

  • Community ecology examines interactions between populations.

    • Factors considered include:

    • Predation

    • Competition

    • Disease

Ecosystems

  • An ecosystem consists of all abiotic factors along with the community of species in a particular area.

  • Ecosystem ecology studies energy flow and chemical cycling among components.

Historical Context in Ecology

  • Rachel Carson (1962) warned against pesticides like DDT causing population declines in non-target organisms.

  • The precautionary principle: “Look before you leap” for environmental decision making.

Impact of Introduced Species

  • Introduced species can dramatically alter ecosystems and cause population explosions in new areas (e.g., African honeybee, Zebra mussel).

  • Complications with predator removal experiments in understanding prey distribution.

Abiotic Factors Affecting Organisms

  • Temperature: Many organisms tolerate specific temperature ranges.

  • Water: Fresh vs. saltwater tolerance.

  • Light: Affects energy availability and ecological processes.

Energy Flow Through Ecosystems

  • LEARNING OBJECTIVE: Describe strategies organisms use to acquire and utilize energy.

  • Organisms require energy for:

    • Maintaining organization

    • Growth

    • Reproduction

    • Temperature regulation strategies:

    • Endotherms: Maintain body temperature metabolically.

    • Ectotherms: Regulate temperature behaviorally (e.g., using sun/shade).

  • Metabolic rates correlate with size: smaller organisms typically have higher metabolic rates.

  • Net energy gain indicates storage/growth; net loss leads to weight loss and potential death.

Sensing Temperature

  • The configuration of heat-sensitive ion channels can vary, allowing different temperature sensitivities.

    • Example Channels: TRPV1 and TRPV3 detect hot temperatures (e.g., TRPV1 reacts to approx 100°F).

    • Hybrid channels may detect intermediate temperatures and have heightened sensitivity.

Biochemical Processes and Temperature

  • Enzyme activity is highly temperature-sensitive:

    • Q10 effect: Increase in reaction rate by 2-3 times for every $10^oC$ rise, until denaturation occurs.

    • Example: Glycogen hydrolysis rate increase in frogs as temperature rises.

Thermoregulation in Mammals

  • Thermoregulation is controlled through feedback mechanisms:

    • Hypothalamus acts as a thermostat.

    • Prompts heat-loss or gain mechanisms.

  • Thyroxin from the thyroid regulates metabolic rate and body temperature.

Adaptations of Ectotherms and Endotherms

  • Ectotherms can produce cryoprotectants to survive subzero temperatures, preventing ice formation in tissues.

  • Examples: Frogs, some arthropods, Arctic fishes.

Climate and Earth’s Biomes

  • Climate Definition: Prevailing weather conditions affecting ecosystems (temperature, light, water).

  • Climate profoundly influences primary productivity and community makeup.

Population Characteristics

  • Populations exhibit size and density with geographical boundaries:

    • Density: Individuals per unit area.

    • Dispersion: Patterns of spacing among individuals.

Population Growth Dynamics

  • Change in population size (ΔN) is defined as:

    • ΔN = Births during time interval − Deaths during time interval.

  • Exponential growth model: Represents idealized populations in unlimited environments, expressed mathematically as: dNdt=B−D\frac{dN}{dt} = B - D where:

    • N = population size

    • B = births

    • D = deaths

Logistic Population Growth

  • Regulated by the carrying capacity (K), the maximum sustainable population size in an environment.

  • The logistic growth model shows:

    • Initial lag phase, followed by rapid growth until resources become limited.

    • Mathematical model: dNdt=rmaxN(K−N)\frac{dN}{dt} = r_{max} N (K - N)
      where:

    • r = maximum per capita growth rate

Interactions and Biodiversity

  • Diversity Index Calculation: Measure community structure through species composition and diversity.

  • Example of Simpson's Diversity Index: Diversity Index=1−Σn2N2Diversity \, Index = 1 - \Sigma \frac{n^2}{N^2} where:

    • n = number of individuals of a particular species

    • N = total number of individuals.

Interspecific Interactions

  • Types of interactions include:

    • Mutualism: Both species benefit.

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

  • Examples: Barnacles on whales; predator/prey dynamics.

Coevolution and Adaptation

  • Coevolution involves reciprocal adaptations between interacting species (e.g., speed adaptations in predators and prey).

Trophic Structure

  • Food Chain: Represents energy transfer from photosynthetic organisms through various trophic levels to herbivores and carnivores.

  • The food web is more complex than a simple chain, displaying multiple interactions.

Energy Flow and Ecosystem Function

  • Autotrophs: Primary producers that convert sunlight into chemical energy via photosynthesis.

  • Energy loss occurs at each trophic level due to the second law of thermodynamics; only about 10% is transferred to the next level, causing biological magnification of toxins (e.g., DDT in food webs).

Chemical Cycling in Ecosystems

  • Nutrient cycles (e.g., carbon, nitrogen cycles) deal with the transformation and transfer of nutrients through various stages.

  • Human activities (agriculture, pollution) can disrupt these cycles, leading to increased environmental concentrations of harmful substances and biodiversity loss.