AP Biology Ecology Unit

Chapter 52: An Introduction to Ecology and the Biosphere:

Earth’s Climate Varies by Latitude and Season and is Changing Rapidly:

• <<Ecology: the scientific study of the interactions between organisms and the environment<<
  • these interactions are organized in a hierarchy from the individual organism to the entire planet
• Climate: the long-term prevailing weather conditions in a given area
  • Four Key Components:
  • temperature
  • Precipitation
  • Sunlight
  • Wind
  • Climate patterns can be described in terms of two scales:
  • Macroclimate: work at the global, regional, or local level
    • the changing angle of the sun over the year, bodies of water, and mountains exert seasonal, regional, and local effects
  • Microclimate: determined by fine-scale variations such as sunlight and temperature differences under a log compared with the surrounding forest floor
  • Climate Change: a directional change to the global climate that lasts three decades or more (as opposed to short-term changes in the weather)
  • increasing carbon dioxide and other greenhouse gas concentrations are warming Earth, wind and precipitation patterns are shifting, and extreme weather events are occurring more frequently
  • changes in climate can alter the population sizes or distribution of many species, some species will not be able to shift their ranges quickly enough to survive

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The Distribution of Terrestrial Biomes Controlled by Climate and Disturbance:

• Biomes: are the major types of ecosystems that occupy very broad geographic regions
• The importance of climate, especially precipitation and temperature, are reflected in the climograph for the major biomes of North America
• Types of Biomes:

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Interactions Between Organisms and the Environment Limit the Distribution of Species:

• Species distributions are a consequence of both ecological factors and evolutionary history
• dispersal of species may be limited by evolutionary history combined with geographic factors
• Biotic and abiotic factors also limit distribution:
  • Biotic Factors: include interactions with other species through predation and herbivory, parasites, pathogens, and competing organisms
  • Abiotic Factors: the nonliving, chemical, and physical components
  • water, oxygen, salinity, sunlight, and soil
• Both biotic and abiotic factors influence the reproductive fitness of individuals in a population and are major forces of natural selection

Chapter 53: Population Ecology:

Biotic and Abiotic Factors Affect Population Density, Dispersion, and Demographics:

• Population: a group of individuals of a single species living in the same general area

• Population Ecology: explores how biotic and abiotic factors influence the density, distribution, size, and age structure of populations

• Three fundamental characteristics of the organisms in a population are the following:

  • Density: the number of individuals per unit area or volume, increases by births or immigration and decreases by deaths or emigration

• Dispersion: the pattern of spacing among individuals with the boundaries of the population

  • Different types of Dispersion:
  • Clumped: individuals in patches, usually around a required resource
  • Uniform: evenly spaced dispersion is often the result of antagonistic interactions
  • Random: shows unpredictable spacing, occurs in the absence of strong attractions or repulsions among individuals or where resources are relatively constant across an area

• Demography: the study of vital statistics of a population, especially birth, death, and migration rates

• Graphic way to show birth and death rates in a population is a survivorship curve

  

• Type I Survivorship Curve: shows low death rates during early life and midlife; then the death rate increases sharply in older age groups

  • typical for large organisms with long life spans

• Type II Survivorship Curve: shows a constant death rate over the organisms life span

  • These organisms are usually heavily preyed upon, so individuals die before reaching old age

• Type III Survivorship Curve: shows very high early death rates, then a flat rate for the few surviving until reaching the older age groups

  • Many bird species show a high death rate for the first year, then a slowing rate for the rest of their lives

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The Exponential Model Describes Population Growth in an Idealized, Unlimited Environment:

• Exponential Population: growth refers to population growth under ideal conditions

  • any species regardless of its life history, is capable of exponential growth if resources are abundant

  

The Logistic Model Describes How a Population Grows More Slowly as it Nears it Carrying Capacity:

• Carrying Capacity: a population defined as the maximum population size that a certain environment can support at a particular time with no degradation of the habitat

• Not taking immigration and emigration into consideration, a population’s growth rate (per-capita increase) equals birth rate minus death rate: dN/dt = B - D

• Logistic Growth Model: the per-capita rate of increase declines as carrying capacity is reached

• Construct the logistic model by starting with the exponential model and adding an expression that reduces the per-capita rate of increase as N approaches K: dN/dt = rmaxN(K-N)/K

  

Life History Traits are Products of Natural Selection:

• traits that affect an organism’s schedule of reproduction and survival make up its life history

• Life histories have three main components:

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  1. How early in the life cycle does reproduction begin?
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  1. How often does the organism reproduce? Some have one big reproductive event
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  1. How many offspring per reproductive event?

• Life history traits are evolutionary outcomes not conscious decisions by organisms

  • There are trade offs between high rates of reproduction and percentages of surviving offspring

• K-Selection: Selection of life history traits that are sensitive to population density and carrying capacity

  • operates in populations living close to the density imposed by the carrying capacity
  • associated with the logistic growth model

• R-Selection: selection for traits that maximize reproductive success in uncrowded environments

  • associated with exponential growth model

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Density-Dependent Factors Regulate Population Growth

• Density Independent: When the death rate does not change with an increase in population density
• Density-Dependent Factors” a death rate that rises as population density rise and a birth rate that falls as population density rises
  • Examples of the major factors that reduce birth rates or increase death rates include the following
  • Competition for Resources: as population density increases, competition for resources intensifies (can include competition for food, space, or essential nutrients)
  • Territoriality: available space for territories or nesting may be limited, thus controlling the population
  • Disease: increasing densities allow for easier transmission of diseases
  • Predation: as prey populations increase, predators may find the prey more easily
  • Density-dependent factors regulate population size by negative feedback
• All populations exhibit some size fluctuations
  • many populations undergo regular boom-and-bust population cycles that are influenced by complex interactions between biotic and abiotic factors

There

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The Human Population is no Longer Growing Exponentially but is Still Increasing:

• Demographic Transition: occurs when a population goes from high birth rates and death rates to low birth rates and low death rates
  • can take up to 150 years to complete
• Age Structure Pyramids: show the relative number of individuals of each age in a population and can be used to predict and explain many demographic patterns
• Ecological Footprint: refers to the total land and water area needed for all the resources a person consumes in a population

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Chapter 54: Community Ecology:

Interactions Between Species Can Help, Harm, or Have no Effect on the Individuals Involved:

• Community: group of populations of different species living close enough to interact with each other
• Interspecific Interactions: may be positive, negative, or neutral and include competition, predation, herbivory, parasitism, mutualism, and commensalism
  • Inter: between different groups
  • Intra: within the same group
• Interspecific Competition: occurs when resources are in short supply
  • Competition is a -/- interaction between the species involved
  • natural selection favors strategies that reduce competition
• Central to the idea of competition and community structure are these two concepts:
  • Competitive Exclusion Principle: states that when two species are fighting over a resource, eventually the one with the slight reproductive advantage will eliminate the other
  • Ecological Niche: the sum of total biotic and abiotic resources that the species uses in its environment
  • Fundamental Niche: the niche potentially occupied by the species
  • Realized Niche: the portion of the fundamental niche the species actually occupies
• Predation: a +/- interaction between two species in which one species (the predator) eats the other species (the prey)
• Animals display a variety of defensive adaptations from predation, including:
  • Cryptic Coloration: the animal is camouflaged by its coloring
  • Aposematic Coloration: warning coloration, when a poisonous animal is brightly colored as a warning to other animals
  • Batesian Mimicry: referring to a situation in which a harmless species has evolved to mimic the coloration of an unpalatable or harmful species
  • Mullerian Mimicry: 2 bad-tasting species resemble each other, ostensibly so that predators will learn to avoid them equally
• Herbivory: a +/- interaction in which an herbivore eats part of a plant or alga
• Parasitism: +/- interaction in which the parasite derives its nourishment from its host
• Mutualism: an interspecific interaction that benefits both species (+/+)
• Commensalism: benefits one of the species but neither harms nor helps the other species

Diversity and Trophic Structure Characterize Biological Communities:

• Species Diversity: measures the number of different species in a community (species richness) and the relative abundance of each species

  • a community with an even species abundance is more diverse than one in which one or two species are abundant and the others are rare

• Communities that are more diverse generally have greater productivity and are more stable than those that are less diverse

  • means that communities with little diversity are less energy efficient and less resistant to changes in the environment

• Ecologists use many tools to compare the diversity of communities

  • often interested in how a community has changed over time or between communities at the same point in time

  

• Trophic Structure: refers to the feeding relationships among the organisms

• Trophic Levels: the links in the trophic structure of a community

• Energy is transferred upward in a food chain - from the plants and other autotrophs (primary producers) through herbivores (primary consumers) to carnivores (secondary, tertiary, and quaternary consumers)

  • this transfer of energy from one trophic level to another is referred to as a food chain
  • Food Webs: consist of two or more food chains linked together

• Energy is lost at each level of the food chain: 10% rule

• Dominant Species: have the highest biomass

  • Biomass: the sum weight of all the members of a population

• Keystone Species: exert control on the community structure by their important ecological niche

  • are usually not the most abundant, but they occupy pivotal ecological roles - when removed the ecosystem often collapses

Disturbance Influences Species Diversity and Composition:

• A disturbance - storm, fire, flood, drought, or human activity - changes a community by removing organisms or changing resource availability: disturbance is not necessarily bad for a community
• Intermediate Disturbance Hypothesis: states that modern levels of disturbance create conditions that foster greater species diversity than do low or high levels of disturbance
• Ecological Succession: refers to transitions in species concentration in a certain area over ecological time
  • Primary Succession: plants and animals gradually invade a region that was virtually lifeless, where soil has not yet formed
  • Secondary Succession: occurs when an existing community has been cleared by a disturbance that leaves the soil intact

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