Ecology and Population Ecology Notes

Ecology

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

Intro to Ecology

  • Concept: Interactions between organisms and the environment limit the distribution of species.
  • Example Learning Outcome: Describe climatological and geographical factors that limit species' ranges.
  • Concept: Population growth and size are determined by rates of birth and death.
  • Example Learning Outcome: Apply exponential and logistic growth models to predict patterns of change in population size.
  • Concept: Density-dependent and density-independent factors influence population growth.
  • Example Learning Outcome: Discriminate between density-dependent and density-independent limits on population growth.

Introduction to Ecology

  • Focuses on the distribution of species.

Species Distribution

  • Species of organisms live in specific places.
  • No species is found everywhere on Earth.
  • Species have evolved with traits that provide advantages in particular environments.
    • Climate.
    • Temperature.
    • Water availability.
    • Amount of precipitation per year.
    • Seasonality of precipitation.
  • Primary producers: autotrophs are the source of food for other organisms.

Climate Variation

  • Climate varies with latitude and altitude.
  • Orientation toward the sun affects temperature.
    • The equator has direct exposure to the sun.
    • At the poles:
      • Light is spread out.
      • Light goes through more atmosphere.
  • Going from the Equator to the poles, seasonal changes in temperature are observed, which is a consequence of Earth’s tilt relative to its plane of revolution around the sun.
    • Northern Hemisphere tilts towards the sun from April to September.
    • Southern Hemisphere tilts toward the sun from September to April.
  • At high altitudes, air is less dense, holds less water, and is cooler.
  • High altitudes provide similar conditions to high latitude.

Climate Effects on Winds and Precipitation

  • Warm air holds moisture.
  • Warm air rises and cools.
  • As it cools, moisture precipitates.
    • Tropical forests: warm and wet.
  • Cool, dry air is displaced by rising moist air and sinks, creating subtropical deserts which are warm and dry.

Winds and the Coriolis Effect

  • As the Earth rotates, air circulates.
  • The rotation is faster at the equator than at the poles.
  • Prevailing winds move ocean currents.
  • Currents can warm high latitudes and cool low latitudes due to the Coriolis effect.

Global Circulation Driven by Wind Patterns

  • The trade winds push water toward the equator, where it moves westward until it reaches a continent, then moves north or south along the coast, forming great circular currents called gyres.
  • The Equatorial Countercurrent arises between the hemispheric gyres.

Geographical Influences on Climate

  • Land near oceans sees milder temperatures because water has high specific heat.
  • Mountain ranges can produce rain shadows.
    • As air rises up a slope, it cools and releases water.
    • On the leeward side, air is dry, creating a desert.

Adaptations to Specific Climates

  • Most organisms cannot live outside a defined range of temperatures.
  • Below 0∘C0^\circ C, water freezes, and ice crystals in cells disrupt membranes.
  • If it is too hot, proteins lose structure, and enzymes cannot function.
  • Temperate climates may have extreme temperatures, but not for prolonged periods.
  • Adaptations are specialized traits that allow an organism to survive otherwise unfavorable conditions.
    • Example: The Alaskan frog can be 65% frozen, but the ice is in extracellular spaces.
  • Some plants and fish can tolerate below 0∘0^\circ conditions by maintaining high concentrations of compounds that serve as antifreeze.

Behavioral Adaptations

  • Many species can survive unfavorable (too cold, too hot) conditions by altering behavior.
    • Hibernation in winter, aestivation in summer.
    • Burrow into protected habitat, slow metabolism.
    • Migration to favorable conditions.

Biomes

  • A biome is a regional land area, defined by climate and geography (terrestrial).
  • Characterized by ecologically similar organisms.
  • Vegetation is the primary character, providing:
    • Food.
    • Habitat.
    • Shelter against weather.
    • Protection against predators.
    • Nesting sites for offspring.

Types of Biomes

  • Tropical rain forests: warm, wet, high productivity, high diversity.
  • Deserts: hot or cold; dry: productivity limited by water.
  • Temperate hardwood woodlands: seasonal variation in temperature, wet, high productivity.
  • Temperate grasslands: drier than woodlands.
  • Chaparral: hot, dry summers, cool, wet winters.
  • Temperate evergreen forests.
  • Taiga and tundra: cold, limited precipitation.

Terrestrial Biomes and Climate

  • Terrestrial biomes reflect average annual temperature and precipitation.

Global Distribution of Terrestrial Biomes

  • Map showing the distribution of tropical rainforests, tropical deciduous forests, thorn forests, tropical savannas, hot deserts, chaparral, cold deserts, high mountains (boreal forest and tundra), temperate evergreen forests, temperate deciduous forests, boreal forests, arctic tundra, temperate grasslands, and polar ice caps.

Tallgrass Prairie

  • Grassland, drier than woodlands.
  • Fires shape the landscape.
    • Most trees are killed by fires.
  • Herbaceous perennials dominate.
    • Deep roots hold and enrich the soil.
  • Grasses: C4 photosynthesis.
  • Forbs (nonwoody, nongrass angiosperms).
  • Corn has replaced prairie.
    • Soil is no longer held: erodes.

Aquatic Environments

  • Oceans are continuous, but marine species are not uniformly distributed.
  • Life zones are defined by illumination: shallow, intermediate, and deep.

Fresh Water

  • Rivers and lakes.
  • Also, variation in illumination.
  • Nutrients are circulated each year by overturn.
  • Estuaries: where fresh and salt water meet.

Biogeography

  • Deals with the distribution of species.
  • Influenced by climate and evolutionary history.
  • Range boundaries:
    • Assemblages of species change dramatically.
    • Represent barriers to dispersal.
    • Current or ancient.

Biogeographical Areas

  • Defined by barriers that prevent the dispersal of species.

Dispersal Barriers

  • Topographical barriers:
    • Mountain ranges.
    • Rivers, lakes.
    • Oceans/continent.
  • Wallace's line separates two distinct modern terrestrial faunas.

Continental Drift

  • There are currently 7 continents.
  • Pangea was a contiguous landmass, then Laurasia (North) and Gondwana (South).
  • Ancestral species were on a common landmass.
    • As they moved apart, they mutated independently under different selection pressures, and species diverged.
    • Species become endemic.
  • Land masses can join, e.g., North and South America.

Modern Countries/Pangea

  • A map showing how modern countries fit into the Pangea landmass.

Area Phylogenies

  • Use the current geographical distribution of related species in combination with an understanding of their relatedness to uncover the history of speciation.

Population Ecology

  • Population growth and size are determined by rates of birth and death.
  • Density-dependent and density-independent factors influence population growth.
  • Apply exponential and logistic growth models to predict patterns of change in population size.
  • Discriminate between density-dependent and density-independent limits on population growth.

Populations

  • An interacting group of members of a species.
  • Defined area: range.
  • Density: How many per area or volume?
  • How are they distributed?
  • Measured at a defined time.
  • How might the size change with time?

Range

  • Most species have a limited geographical distribution.
  • Even humans don’t live everywhere!
  • Dolphins: in all oceans.
  • Other extreme: Devil’s Hole pupfish.
  • Endemic: a species limited to a defined location.
  • Cosmopolitan: distributed widely.
  • Ranges can change as the environment changes or a species expands into new areas.
    • Example: Cattle egret, evolved in Africa, arrived in South America in the 1930s, and was in most of North America by the 1960s.

Dispersion

  • Population in a defined area can be distributed in different ways:
    • Clumped together in small groups (being together is beneficial; the environment is not uniform).
    • Equal distances among individuals (being together is harmful).
    • Random (proximity is not important).

Population Changes

  • Individuals are born and die, and there is also immigration and emigration.
  • How to measure population size:
    • Count them (full census).
    • Estimate from representative samples.

Estimating Population Sizes

  • Capture-recapture method:
    1. Capture a random sample of individuals from the population of interest and mark each captured individual.
    2. Release the marked individuals and allow an appropriate amount of time for them to merge completely with unmarked individuals in the population.
    3. Capture a second random sample of individuals. Determine both the total number of individuals captured and the number of marked individuals in this sample.
    4. Estimate the total population size NN using the equation: N=n<em>1×n</em>2MN = \frac{n<em>1 \times n</em>2}{M}
      • n1n_1 = the total number of individuals in the first sample (captured, marked, and released).
      • n2n_2 = the total number of individuals in the second sample.
      • MM = the number of marked individuals recaptured in the second sample.

Demographics

  • Ages of individuals in the population influence whether births and deaths are likely.
    • Old members are past reproduction.
    • Juveniles are not yet reproducing.
  • Species vary with respect to the reproductive period.

Life Tables

  • Predict future for a population.
  • How long is an individual of a given age likely to live?

Fecundity Tables

  • How likely is an individual of a given age to produce offspring?
  • Factors other than age can influence reproduction.

Environment and Life Histories

  • Both how long an individual lives and how many offspring it produces is highly dependent on the environment.
    • Food, weather, predators.
  • Affects:
    • When they start reproducing.
    • How many times per year they reproduce.
    • Number of offspring per brood.

Survivorship Curves

  • Type 1: Most individuals survive to reproduction. Few offspring, long lives (e.g., humans).
  • Type 2: Constant risk of mortality at all ages (e.g., most birds).
  • Type 3: Most die as juveniles. Many offspring, low parental care (e.g., mollusks, insects).

Life History Strategies

  • Organisms partition time and energy into growth, maintenance, and reproduction.
  • Variable, dependent on resources and mortality.
  • Affect how fast populations grow: r=b−dr = b - d
    • rate of population growth = rate of births minus rate of deaths

Limits to Population Densities

  • If resources (food, habitat) are unlimited, how big can populations get?
    • Exponential growth can occur theoretically, but only for short periods.

Carrying Capacity

  • Exponential growth ends when something needed becomes limited: food, nesting sites, shelter.
  • The environment can provide only a limited amount of such a resource.
  • Has a carrying capacity (K).
  • As the size of population reaches K, growth in population size slows “logistic” growth curve.

r- vs. K-Strategists

  • r: rate of population growth.
  • K: carrying capacity.
  • Life histories favor different strategies for species survival.
    • r strategists: high rates of reproduction, broad range of habitats, many offspring, limited parental investment, population size fluctuates.
    • K strategists: population steady near K, narrow range, high parental investment, long lives.

Population Regulation Factors

  • Density dependent (biotic):
    • Food can become scarce; poor nutrition slows birth rate and speeds up death rate.
    • Large populations attract predators.
    • Dense populations pass disease among members.
  • Density independent (abiotic):
    • Natural disturbances (extreme cold, hurricanes) reduce populations regardless of density.

Variation in Population Density

  • Why are some species abundant and others rare in their habitats?
    • Generalist vs. specialist for food.
    • Smaller vs. larger bodies.
    • Social vs. solitary.
    • Introduced vs. native.
    • Predators and pathogens haven’t yet evolved to challenge.

Mosaics of Populations

  • Within its range, no species is uniformly distributed.
    • Patchy.
    • Gene flow (mating) occurs in patches, less likely between them.
  • Metapopulation:
    • Provides new individuals if a particular patch dies off.
    • Requires “corridors”- physical connections among patches.
  • Islands: populations isolated- no corridors possible.
  • Conversion of natural areas to development, agriculture- patches of natural areas are equivalent to islands.

Colonization

  • Patches of habitat being colonized and becoming extinct, with recolonization happening in some areas.

Population Management

  • Life history strategies inform population management.
  • Cod was once extremely abundant.
    • Efficient means of harvesting led to severe population declines.
  • Striped bass were also abundant but severely overfished.
    • Regulations preventing fishing allowed populations to recover.