Topic 10: Ecology Carlo Byrd, Cristobal Lopez, Clarissa Maldonado, Alyssa Martinez, Dorian Trinh


Major types of ecosystem that occupy very broad geographic regions.


Climograph or some major biomes in North America

Structure and distribution os terrestrial biomes are controlled by climate and distrubance

8 terrestrial biomes:

  • Savannas
  • Desert
  • Chaparral
  • Temperate grassland
  • Tundra
  • Temperate broadleaf forest
  • Coniferous forest
  • Tropical rainforest

Aquatic biomes are classified into freshwater biomes and marine biomes.


  • Characterized by grasses and some trees
  • Dominant herbivores: insects, such as ants and termites
  • Dominant abiotic factor: fire - many plants are adapted for fire
  • Plant growth is substantial during rainy season
  • Large grazing mammals must migrate during regular seasons of drought


  • Sparse rainfall
  • Desert plants and animals are adapted to absorb and store water
  • Contains many CAM plants and plants with adaptions that prevent animals from consuming them
  • Temperature (either hot or cold) is usually very extreme


  • Dominated by dense, spiny, evergreen shrubs
  • Coastal areas with mild, rainy winters and long, hot, dry summers
  • Plants adapted to fires

Temperate Grasslands

  • Marked by seasonal drought with occasional fires
  • Has large grazing mammals
  • These factors prevent seasonal growth of trees
  • Soil is rich in nutrients which makes it good for agriculture

Temperate Broadleaf Forest

  • Marked by dense strands of deciduous trees that requires sufficient moisture
  • More open than rainforests
  • Stratified-top layer has 1-2 strata of trees; beneath are shrubs; under that is herbaceous stratam

Coniferous Forest

  • Dominated by cone-bearing trees such as pine, fir, and spruce
  • Shape of conifers prevents much snowfall from accumulating on the tree's branches


  • Marked by permafrost (permanently frozen layer of soil)
  • Very cold temperatures
  • High winds
  • Little rainfall
  • Supports no trees or plants
  • Accounts for 20% of Earth's terrestrial surface

Tropical Rainforest

  • Pronounced vertical stratification
  • Dense canopy; so little light breaks through
  • Marked by epiphytes, plants that grow on other plants instead of soil
  • Varied rainfall
  • Greatest biodiversity of all terrestrial biomes

Aquatic Biomes

  • Make up the largest part of the biopshere
  • Biomes are classified as freshwater and marine biomes
  • All aquatic biomes display vertical stratification, which leads to:
  1. Photic zone - there is enough light for photosynthesis to occur
  2. Aphotic zone - very little light penetrates
  3. Benthic zone - bottoms of biome; made up of sand, inorganic matter, and organic sediments
  4. Thermoclines - narrow layer of fast temperature change that separate a warm upper layer of water and cold, deeper water

Freshwater Biome

  • 2 types of freshwater:
  1. Standing bodies of water (lakes and wetlands)
  2. Moving bodies of water (streams and rivers)
  • In lakes, communities are distributed according to water depth.
  • Oligotrophic lakes - deep lakes that are nutrient-poor, oxygen-rich, and contain sparse plankton
  • Eutrophic lakes - shallow lakes that are nutrient-rich, oxygen-poo, and high phytoplankton concentration
  • In streams and rivers, organisms are distributed in vertical zones and from headwaters to the mouth.

Marine Biomes

  • Intertidal zone - land meets water, is periodically submerged and exposed by the twice-daily tides
  • Necrotic zone - shallow water over the continental shelves
  • Pelagic zone - vast realm of open blue water
  • Coral reef - a biome created by a group of cnidarians that secret hard calcium carbonate shells; the most productive ecosystems on earth


A lake that is nutrient-rich and that supports a vast array of algae is said to be

  1. oligotrophic.
  2. abyssal.
  3. littorial.
  4. eutrophic.
  5. limnetic.
4. eutrophic.

Which of the following terms is used to describe major types of ecosystems that occupy broad geographic regions?

  1. biome
  2. community
  3. chaparral
  4. trophic level
  5. photic zone
1. biome

Which of the following is the term that refers to the layer of light penetration in aquatic ecosystems?

  1. littoral zone
  2. limnetic zone
  3. photic zone
  4. benthic zone
  5. aphotic zone
3. photic zone


A group of individuals of a single species living in the same general area. It studies how biotic and abiotic factors influence the density, distribution, size, and age structure of populations.

Fundamental Characteristics of a Population

Density - number of individuals per unit area or volume

Dispersion - pattern of spacing among individuals within the boundaries of the population

Demography - study of vital statistic of a population, especially birth and death rates

  • Type I - low death rates during early and midlife, then the death rate increases sharply in order age groups
  • Type II - constant death rate over the organism's life span
  • Type III - very high early death rates, then a flat rate for the few surviving to older age groups

Exponential Growth

Population growth under ideal conditions.

Logistic Growth

Per capita rate of increase declines, carrying capacity is reached.

dN / dT = rN(K-N) / K

Carrying capacity - the maximum population size that a certain environment can support of a particular time with no degradation of the habitat

K & R Selection

K-selection - selection of life history traits that are sensitive to population density and carrying capacity

r-selection - selection for life history traits that maximize reproductive success

Age-Structure Pyramids

Relative number of individuals of each age in a population, and can be used to predict and explain many demographic patterns.


A Type I survivorship curve is level at first, with a rapid increase in mortality in old age. This type of curve is

  1. typical of many invertebrates that produce large numbers of offspring.
  2. typical of humans and other large mammals.
  3. found most often in r-selected populations.
  4. almost never found in nature.
  5. typical of all species of birds.
2. typical of humans and other large mammals.

The human population is growing such an alarmingly fast rate because

  1. technology has increased our carrying capacity.
  2. the death rate has greatly decreased since the Industrial Revolution.
  3. the age structure of many countries is highly skewed toward younger ages.
  4. fertility rates in many developing countries are above the 2.1 children per female replacement.
  5. All of the above are true
5. All of the above are true

According to this graph of the population growth of fur seals in what year did the population first reach its carrying capacity?

  1. 1925
  2. 1930
  3. 1940
  4. 1950
3. 1940


A group of populations of different species living close enough to interact. For one species, interspecific interactions may be positive, negative, or neutral.

Interspecific Competition ( - / - )

Occurs when resources are in short supply. These two concepts are the central idea of competition and community structure:

  • The competitive exclusion principle states that when two species are competing for resource, the one with the reproductive advantage will eventually eliminate the other
  • An ecological niche is the total of biotic and abiotic resources that a species uses. Fundamental niche is the niche potentially occupied by the species, while realized niche is the portion of the fundamental niche the species actually occupies.

Predation ( + / - )

One species (predator) eats the other species (prey). Defenses for predators include the following:

Cryptic coloration - animal is camouflaged by its coloring
Aposematic (warning coloration) - a poisonous animal is brightly colored as a warning to other animals
Batesian mimicry - a harmless animal evolved to mimic the coloration of a harmful or unpalatable one
Müllerian mimicry - two bad-tasting species resemble each other so that predators learn to avoid both of them

Herbivory ( + / - )

A herbivore eats part of a plant or alga. A plant's main defenses are chemical toxins, spines, and thorns.


Occurs when individuals of two or more species live in direct contact with one another.

Parasitism (+/-) - parasite derives nourishment from its host and may have a significant effect on the survival, reproduction, and density of the host population
Mutualism (+/+) - benefits both species
Commensalism (+/0) - benefits one species but the other species is neither harmed nor helped

Dominant and Keystone Species

Dominant species - have the highest biomass or the most abundant

Keystone species - control the community structure by their important ecological niches

Trophic Structure

The feeding relationships among organisms.

Trophic levels - links in the trophic structure of a community


Changes a community by removing organisms or changing resource availability (e.g. storm, fire, flood, drought, human activity). The intermediate disturbance hypothesis states that moderate levels of disturbance fosters greater species diversity than low or high levels of disturbance.

Ecological succession - transitions in species composition in a certain area over a period of time

  • Primary succession - a virtually lifeless area with no soil gradually fosters plants and animals (e.g. a new volcanic island)
  • Secondary succession - an existing community has been cleared by a disturbance, leaving the soil intact


When one species was removed from a tide pool, the species richness became significantly reduced. The removed species was probably

  1. a strong competitor.
  2. a potent parasite.
  3. a resource partitioner.
  4. a keystone species.
  5. the species with the highest relative abundance.
4. a keystone species.

Which of the following interspecific interactions is not an example of a +/- interaction?

  1. ectoparasite and host
  2. herbivore and plant
  3. honeybee and flower
  4. pathogen and host
  5. carnivore and prey
3. honeybee and flower

A fire cleared a large area of forest in Yellow Stone National Park in the 1980's. When the first plants pioneered this burned area, this was an example of

  1. primary succession.
  2. secondary succession.
  3. biological evolution.
  4. a keystone species.
  5. the top-down model.
2. secondary succession


Sum of all organisms within its boundaries and all the abiotic factors with which they interact.

Flow of Energy

Primary producers - autotrophs ("self-feeders"); support all other organisms in the ecosystem

Heterotrophs - eat other organisms

  • Herbivores - consume primary producers (primary consumer)
  • Carnivores - consume other heterotrophs (secondary or tertiary consumers)
  • Detritivores (Decomposers) - consumers get energy from nonliving organic material

Primary Production

Amount of light energy converted to chemical energy by autotrophs

  • Gross Primary Production (GPP) - total primary production of an ecosystem
  • Net Primary Production (NPP) - primary production minus the energy used by autotrophs in their "autotrophic respiration" (Ra)

NPP = GPP - Ra

Carrying Capacity

The maximum population size that a certain environment can support at a particular time with no degradation of habitat.

A population's growth rate equals birth rate minus death rate.

dN / dT = B - D

Energy Transfer

Energy is lost at each level of transfer as heat, for movement or reproduction or any life processes that consume energy.

10% of usable energy is passed on to each level. A primary consumer would get 10% of the energy the autotroph had. A secondary consumer would get 10% of the energy the primary consumer had, which is 1% of what the autotroph had.

The loss of energy from trophic level to trophic level is one of the factors that keeps the food chains so short.


Which statement best describes energy transfer in a food web?

  1. Energy is transferred to consumers, which convert it to nitrogen compounds and use ti synthesize amino acids.
  2. Energy from producers is converted into oxygen and transferred to consumers.
  3. Energy from the sun is stored in green plants and transferred to consumers.
  4. Energy is transferred to consumers that use it to synthesize food.
  5. Energy moves from autotrophs to heterotrophs to decomposers, which convert it to a form producers can use again.
3. Energy from the sun is stored in green plants and transferred to consumers.

The carrying capacity of a population is defined as

  1. the amount of time the parents in the population spend rearing and nurturing their offspring.
  2. the maximum population size that a certain environment can support at a particular time.
  3. the amount of vegetation that a certain geographic area can support.
  4. the number of different types of species a biome can support.
  5. the number of different genes a population can carry at a particular time.
2. the maximum population size that a certain environment can support at a particular time.

Which of the following is the major primary producer in a savanna ecosystem?

  1. lion
  2. gazelle
  3. grass
  4. snake
  5. diatom
3. grass


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