Ecology and Population Ecology Notes

Ecology

• Ecology is the scientific study of:
  • The processes influencing the distribution and abundance of organisms.
  • The interactions among organisms.
  • The interactions between organisms and the environment.
  • The transformation and flux of energy and matter.

Ecological Hierarchy

• Ecologists study at different levels:
  • Organismal: How physiology and behavior meet environmental challenges.
    • Example: Cold-blooded alligators sunning to warm up.
    • Example: Camels storing water in arid environments.
  • Population.
  • Community.
  • Ecosystem.
  • Landscape: Controls on the exchange of energy, materials, and organisms across connected ecosystems.
  • Biosphere/Global.

Abiotic and Biotic Factors

• Abiotic factors (non-living):
  • Climate (Temperature and Precipitation).
  • Light and nutrient availability.
  • Temperature: Has a strong effect on where terrestrial organisms live.
  • Precipitation.
  • Amount of Light: Has a strong effect on where aquatic organisms live.
  • Nutrients.
• Biotic factors (living):
  • Competition.
  • Predation.
  • Pathogens.

Species Distribution

• Terrestrial ecosystems:
  • Species distributions are strongly driven by temperature and precipitation.
  • Figure 52.11: Climograph for major North American biomes, plotting annual mean temperature vs. annual mean precipitation.
• Aquatic ecosystems:
  • Species distributions are strongly driven by light and nutrient availability.
• Tolerance to abiotic factors determines a species’ potential range.
  • Species have varying tolerance ranges for abiotic factors; some have wide tolerances, while others have narrow ones.
• Species distribution is determined by combinations of Biotic and Abiotic factors.
  • Example: Saguaro Cactus
    • Located in Sonoran Desert.
    • Range limited by temperature.
    • Not found in some suitable areas due to seed predation limiting spread.
  • Example: Long-spined Urchins
    • Located in Eastern Australia.
    • Consume kelp forests
    • Range limited by temperature
    • Expanding south with climate change.
• Abiotic (environmental) factors often limit the potential range of organisms.
• Biotic (organismal) factors often limit the actual distribution of organisms within those potential ranges.

Ecological and Evolutionary Change

• Ecological change alters selective pressures in a population.
• Evolutionary change alters the outcome of ecological interactions.
• Figure 52.24: Demonstrates the reciprocal effects of ecological and evolutionary change.

Population Ecology

• Population Ecology studies the dynamics of species populations and their interactions with the environment.
• A population is a group of individuals of the same species that live in the same area.

Population Characteristics

• Includes Density, Dispersion, Population Structure, and Population Rates.

Population Structure

*Make-up of individuals in the population:
* Age and sex distributions.

Sex Ratio

• Number of males : number of females.
  • Primary (1^o) – fertilization (typically 1:1).
  • Secondary (2^o) – birth/hatching.
  • Tertiary (3^o) – later stage of life (adult).
• Ratio becomes more skewed with age.
  • Example: Elk Prenatal Sex Ratio (53:47) vs Adult Sex Ratio (23:77)
  • Example: Richardson’s ground squirrel Prenatal Sex Ratio (50:50) vs Adult Sex Ratio (11:89)
• Several Hypotheses (not mutually exclusive) for skewed tertiary sex ratio in non-humans. Reproduction-related stresses. Dispersal increases risk of predation in dispersing sex. Intraspecific competition (Dominance status and Energetic requirements).

Population Age Structure

• Percentage of individuals in different ages or age groups in the population.
• Age structure diagrams, useful for predicting a population’s future growth trend and can highlight future socio-economic conditions in a population.
• Age groups based on reproductive status: Pre-reproductive, Reproductive, Post-reproductive.
  • Pyramid shaped (Zambia): Many juveniles, few seniors -> population is growing.
  • Bell (dome) shaped (United States): Balanced across reproductive groups -> population is stable.
  • Urn shaped (Italy): Few juveniles, many seniors -> population is declining.
• The Demography of the World Population from 1950 to 2100.
  • Median age increasing from 23.6 years (1950) to 41.6 years (2100).

Population Rates

• Birth rate (b): # of births / population.
• Death rate (d): # of deaths / population.
• Fecundity: # of offspring/time (per female), generally limited by # of gametes (eggs).
• Generation time: Time period from birth of individuals to birth of their offspring.
  • Generation time is related to body size.
• Survivorship: Tracks changes in # of individuals in a cohort over time.

Life Table

• Summarizes the survival and reproduction rates of individuals in specific age-groups.
• Built by following a cohort of individuals from birth until death. For sexually reproducing species, often only the females are followed/studied (because they are producing the offspring).
• Used to construct a survivorship curve showing the proportion of individuals alive at each age.

Survivorship Curves

• Species generally follow one of three survivorship curves.
• Differences based on death rates during different life stages:
  • Type 1 (late loss):
    • High survival of offspring.
    • High mortality later in life.
    • Females produce few offspring.
    • High parental investment in care.
    • Many large mammal species (e.g., Humpback whales, African elephants).
  • Type 2 (constant loss):
    • Mortality relatively constant across all ages.
    • Constant proportion die at each age.
    • Some rodents, many invertebrates, lizards, annual plants (e.g., Red-headed agama lizards, Belding’s ground squirrel).
  • Type 3 (early loss):
    • Low survival of offspring.
    • Low mortality among adults.
    • Females produce many offspring.
    • Often no parental investment in care.
    • Long-lived plants (trees), most marine invertebrates, fishes, sea turtles (e.g., Cedar tree releasing pollen, Coral spawning).