Ecology

• The Scope of Ecology

  • Ecology provides the basis for studying the interactions between organisms and their environment.
  • Subfields of Ecology:
  • Organismal (behavior)
  • Population: group of same species in one area
  • Community: all organisms of all species
  • Ecosystem: community + abiotic factors
  • The biosphere refers to the global ecosystem.

  A) global

  B) landscape

  C) ecosystem

  D) community

  E) population

  F) organismal

  
• Environmental Factors

  • Abiotic, or non-living (chemical and physical), factors:
  • Temperature
  • Water
  • Sunlight
  • Wind
  • Substrate (rocks, soil)
  • Nutrients
  • Biotic, or living, factors:
  • Other species
• Biotic Factors:

  • If behavior is not a limitation, other species might be.
  • Competition
  • Predation
  • Parasitism
  • Disease

  
• Abiotic Factors

  • Climate represents the major weather conditions in a particular area
  • Abiotic factors include:
  • Temperature
  • Water
  • Sunlight
  • Wind

  
• Global Climate Patterns

  • Input of solar energy and the movement of Earth influence global climate patterns.

  
• Seasonal Variations

  • Earth’s tilt causes seasonal variations in the intensity of solar radiation.

  
• Air Circulation and Precipitation

  • Variations in solar energy initiates a pattern of air circulation and precipitation.

  
• Mountains

  • Climate patterns along mountain ranges introduce variable abiotic factors
  • As air flows over the windward side and rises, it cools and condenses, forming rain
  • The now dry air continues flowing down the leeward side of the mountain, where it warms as it sinks
  • Warm and dry air --> desert
• Aquatic Biomes

  • Biomes are major types of ecological associations that occupy broad geographic regions of land or water.
  • Aquatic biomes are stratified based on light, depth, and distance form shore.
  • Aquatic biomes encompass both freshwater and saltwater regions.

  
• Dispersion of Aquatic Biomes

  
• Aquatic Biomes

  • Lakes can be oligotrophic (nutrient poor) or eutrophic (nutrient rich)
  • Rivers and streams have different communities associated with the current
  • Wetlands fill with water long enough to support life
  • Estuaries are transition areas during tidal fluctuations
  • Marine aquatic biomes encompass intertidal zones, coral reefs, benthic zones, and pelagic zones
• Biome Distribution

  
• Tropical Rainforest

  • Distribution: equatorial
  • Precipitation: 200-400 cm annually (wet)
  • Temperature: 25-29°C (warm)
  • Characteristics: Diverse plants (stratified) & animals, thin soil
• Savanna

  • Distribution: equatorial
  • Precipitation: seasonal dry/wet 30-50 cm/yr
  • Temperature: 24-29°C (warm)
  • Characteristics: plants adapted to dry, fire prone conditions; herbivorous animals & predators; fertile soil.
• Desert

  • Distribution: 30 N & S latitude
  • Precipitation: 30 cm/yr (dry)
  • Temperature: -30-50C (large range)
  • Characteristics: sparse vegetation including draught tolerant succulents and cacti; animals include snakes, lizards, insects, birds, & rodents (most species are nocturnal)
• Chaparral

  • Distribution: coastal mid-latitudes
  • Precipitation: 30-50 cm/yr; dry summer/wet winter
  • Temperature: 12-40°C (winter/summer)
  • Characteristics: draught tolerant shrubs and small trees, grasses and herbs; animals included herbivores, amphibians, birds, reptiles, & insects
• Temperate Grassland

  • Distribution: mid-latitudes/mid-continents
  • Precipitation: 30-100 cm/yr; dry winter/wet summer
  • Temperature: -10-30°C (winter/summer)
  • Characteristics: fire adapted & draught resistant grasses and forbs; herbivores & prairie dogs; deep fertile soil
• Temperate Deciduous Forest

  • Distribution: mid-latitude/ northern hemisphere
  • Precipitation: 70-200 cm/yr; rain/snow
  • Temperature: 0-30°C (winter/summer)
  • Characteristics: many mammals (hibernating), insects, birds (migrating), etc; forests show vertical layers deciduous trees (seasonal); fertile soils
• Coniferous Forest (Taiga)

  • Distribution: high-latitude/ northern hemisphere
  • Precipitation: 30-70 cm/yr; coastal temperate rainforests
  • Temperature: -70-30°C (long winter/ short summer)
  • Characteristics: largest terrestrial biome on Earth; cone-bearing trees (conifers); diverse mammals, birds, & insects.
• Arctic Tundra

  • Distribution: arctic, high-latitude, northern hem.
  • Precipitation: 20-60 cm/yr
  • Temperature: -30-10°C (long winter/ short summer)
  • Characteristics: permafrost, lichens, & moss; mostly migratory animals & resident herbivores
• Alpine Tundra

  • Distribution: high elevation at all latitudes
  • Precipitation: 100 cm/yr
  • Temperature: -30-10°C (long winter/ short summer)
  • Characteristics: permafrost, lichens, & moss; mostly migratory animals & resident herbivores
• Impact of Ecology

  • Ecology provides a scientific context for evaluating environmental issues.
  • In 1962, Rachel Carson (Silent Spring) warned of problems associated with the used of pesticides such as DDT detrimentally impacting non-target species.
• Dynamic biological processes influence population density

  • A population is a group of individuals of a single species living in the same general area at the same time that can produce viable offspring
• Patterns of Dispersion

  • Environmental and social factors influence spacing of individuals in a population
  • There are three categories of dispersion
  • Clumped
  • Uniform
  • Random
• Clumped Dispersion

  • In a clumped dispersion, individuals aggregate in patches
  • A clumped dispersion may be influenced by resource availability and behavior
  • Ex: wolves living in groups (packs) increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory
• Uniform Dispersion

  • A uniform dispersion is one in which individuals are evenly distributed
  • It may be influenced by social interactions such as territoriality
  • Ex: Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors
• Random Dispersion

  • In a random dispersion, the position of each individual is independent of other individuals
  • Ex: Dandelions grow from windblown seeds that land at random and later germinate
• Demography

  • Demography is the study of the vital statistics of a population and how they change over time
  • Demographic = a portion of a population
  • Death rates and birth rates are of particular interest to demographers
  • Age, gender, etc.
• Survivorship Curves

  • A survivorship curve is a graphic way of representing the data in a life table
  • Different organisms have different survival strategies and therefore have different survivorship curves
  • The survivorship curve for Belding’s ground squirrels shows a relatively constant death rate

  
• Cohort: A group of organisms of the same population born at approximately the same time

  • Ex: human generations
• Survivorship curves can be classified into three general types: Type I, Type II, and Type III

  • Type I typically includes big mammals such as whales, kangaroos, and humans
  • High youth survival rates, most die at old age
  • Type II typically includes small mammals such as squirrels
  • Half of the population dies annually (exponential decay)
  • Type II survivorship includes fish, invertebrates, and bugs
  • Most of population dies at a young age
• Reproductive Rates

  • A reproductive table, or fertility schedule, is an age-specific summary of the reproductive rates in a population
  • It describes reproductive patterns of a population
• Life History Diversity

  • Life histories are very diverse
  • Species that exhibit semelparity, or “big-bang” reproduction, reproduce once and die
  • When they reproduce, many offspring are produced
  • Species that exhibit iteroparity, or repeated reproduction, produce offspring repeatedly
  • When they reproduce, few offspring
  • In animals, parental care of smaller broods may facilitate survival of offspring
• The exponential model describes population growth in an idealized, unlimited environment

  • It is useful to study population growth in an idealized situation
  • Idealized situations help us understand the capacity of species to increase and the conditions that may facilitate this growth
• Exponential population growth results in a J-shaped curve

  
• The J-shaped curve of exponential growth characterizes some rebounding populations

  • Ex: those recently placed under protection
• The logistic growth model includes the concept of carrying capacity

  • Exponential growth cannot be sustained for long in any population
  • A more realistic population model limits growth by incorporating carrying capacity
  • Carrying capacity (K) is the maximum population size the environment can support
  • Limiting factors, such as amount of available land/resources, influence carrying capacity
• The logistic model of population growth produces a sigmoid (S-shaped) curve

  
• Some populations overshoot K before settling down to a relatively stable density

  
• The Logistic Model and Life Histories

  • Life history traits favored by natural selection may vary with population density and environmental conditions
  • K-selection, or density-dependent selection, selects for life history traits that are sensitive to population density
  • Ex: less food --> slow production
  • Think: K = kangaroo
  • r-selection, or density-independent selection, selects for life history traits that maximize reproduction
  • Have many offspring regardless of sustainability
  • Think: R = roaches