Biomes

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.

Desert

• 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

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

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

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

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.

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

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

Age-Structure Pyramids

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

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.

Herbivory ( + / - )

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

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

Disturbance

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

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

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.