Communities & Biomes, p. 1
COMMUNITIES, ECOSYSTEMS & BIOMES
COMMUNITY STRUCTURE (chapter 4)
No species is found in every ecosystem
each is limited by a variety of factors
factors commonly relate to food, water & shelter
Each of the limiting factors varies in amount
In response, each species has (p. 77):
1) optimum condition - best for survival & reproduction
largest population sizes & best reproductive success
2) range of tolerance - conditions in which a species can survive
small populations with minimal or no reproduction
also thought as zone of stress
3) range of intolerance - where species doesn't survive very long
Ecologist describe a species’ optimum conditions as it niche
Each species’ niche varies due to interactions with other species (pp. 83-87)
1) commonly thought as negative and limits a species niche
a) competition = fighting for same food, water & shelter
b) predation & parasitism = limiting by consuming/eating
2) some interactions are positive, thus enhancing a species niche
a) mutualism = living together for common positive goal
lichens (must live as such)
oxpecker & impala (come & go)
b) commensalism = living together, but only one benefits
epiphytes (one plant growing on another) – Spanish moss
The number of species in a community varies widely across the planet
Several factors influence this diversity
1) primary productivity (photosynthesis)
greater amount of light yields more photosynthesis
Communities & Biomes, p. 2
thus we expect more life and more diversity
generally greater near the equator
2) abundance of a species (how many of a species)
a community with greater diversity typically has fewer of each species
no one species is abundant
more common near the equator
3) spatial patterns (2- and 3-dimensional growth)
species can be random, uniform, or clustered in the spacing
many reasons for each pattern
eg. seeds dispersed randomly, but clumped near parent tree
fish clump in schools
birds uniform when they have a territory
4) complexity (number of different interactions)
commonly look at trophic levels (producer, consumer, decomposer)
can even look at layers of vegetation (soil, herbs, shrubs, trees)
BIOMES (Chapter 5)
Definition = a group of ecosystems with a similar potential vegetation
Biomes are defined by their vegetation
Biomes change from one location to another due to climate
temperature – heat in summer, cold in winter, freezing
precipitation – how much, distribution by month
Soils greatly influenced by climate and can create differences within a biome
Book divides biomes into three groups
1. Terrestrial (on land)
2. Freshwater
3. Marine (ocean)
Communities & Biomes, p. 3
TERRESTRIAL BIOMES
Ten well know terrestrial biomes (note fig. 5.3)
Distinguished on two important factors
a) Dominant plant growth form (herbs/grasses, shrubs, trees/forest)
grasslands, shrubs, forests
b) Climate (temperature + precipitation)
tropical, temperate and polar
Note summary chart of biome types, fig 5.2
1) Tropical Moist Forests
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In many areas known as a rainforest: evergreen forests dominant vegetation
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Warm year round – continuous growth
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Wet year round – at least 80 inches rain
* wettest place (South Pacific Islands) over 400 inches a year!
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Most common near equator
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Common on 3 continents: South America, Africa, Asia
2) Tropical Seasonal Forest
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Trees predominant
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Warm year round
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Seasonal rainfall – wet and dry season
* some trees loose leaves in dry season
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Common in: Central America & eastern South America
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Relatively rare biome type
3) Tropical Savanna
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Combination of forest and grasslands
* trees short and commonly have thorns
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Warm year round
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Wet and dry seasons – dry season long
* rainfall lasts only 3-5 months
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Common near equator on east side of continents (South America, Africa, Asia)
* most well known in Africa
Communities & Biomes, p. 4
4) Temperate Deciduous Forest
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Forest predominate
* trees loose leaves in winter – deciduous
* some evergreen forests planted (pine)
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Seasonal temperature changes (temperate zone)
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Generally wet year round (40-80 inches)
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Common in temperate zones: North America, Europe, northern Asia
5) Temperate Shrublands
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Dominated by shrubs and small trees (aka chaparral, Mediterranean)
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Seasonal temperature changes
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Seasonal precipitation (20-40 inches)
* drought during summer
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Common in western North America, Chile (S. Amer.), Australia, and
Europe (along Mediterranean Ocean)
6) Temperate Grasslands
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Dominated by herbs, especially grasses (aka prairie, pampas, steppe)
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Seasonal temperatures – cold winter
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Seasonal precipitation (10-30 inches)
* wetter during summers
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Fire a common feature too
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Well known in: North America, South America, Russia
7) Deserts
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Vegetation scattered, drought resistant
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Temperature variable, two types
a) warm desert – seasonal warm/cool
b) cold desert – polar
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Precipitation minimal: less than 30 inches
* driest in Chile – no rain in 300 years
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Most common 30o north & south equator
* Sahara & Gobi most well know
* also in Chile, in Arizona
Communities & Biomes, p. 5
8) Boreal and Conifer Forests
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Forest predominate (aka taiga in Russia)
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Seasonal temperatures, cold winters
* short growing season – 4 months
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Rainfall variable (20-50 inches)
* not limiting due to cool temperatures
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Common in North America, Russia, and Europe
9) Tundra
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Vegetation sparse, herbs and shrubs
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Very cold, short growing season
* frost possible any month of year
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Relatively dry – 10-30 inches, mostly snow
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Ground commonly frozen in winter and thaws down 1-2 feet in summer
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Common near poles (Arctic) and in high mountains (Alpine)
10) Ice
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Little of no vegetation grows
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Very cold year round
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Commonly dry, less than 10 inches snow
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Around the poles
* Antarctica, Greenland, Iceland
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Also in high mountains as glaciers
FRESHWATER BIOMES
Abundance of freshwater: distinguished by water depth & flow
Include:
1. streams and rivers
2. ponds and lakes
3. wetlands
1) Streams and Rivers
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Characteristics:
generally shallow, flowing water
Communities & Biomes, p. 6
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Location:
* common throughout eastern USA
* less common in west
2) Ponds and Lakes
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Characteristics:
variable depth, non-flowing water
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Features:
depth important due to light penetration
* shallow with vegetation
* deep is open water
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Where:
throughout USA, many man-made
largest natural = Great Lakes
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Note changes in lake structure with water depth, fig 5.19
3) Wetlands
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Characteristics:
generally shallow, seasonally dry
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Types: swamps (trees), marshes (herbs), bogs (saturated ground)
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Where: common along rivers in SC closer to coast
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Wetlands in USA are declining in size and number. See fig. 5.23
MARINE BIOMES
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Ocean and associated coastal areas:
distinguished by depth & salinity
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Include:
* open ocean
* shallow coasts (including reefs)
* estuaries and marshes
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Note terminology relative to ocean water depth & light, fig. 5.14
Communities & Biomes, p. 7
1) Open Ocean
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Characteristics:
variable depth, up to several miles
low nutrients, little life
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Where:
covers about 70% of earth surface
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Note productivity in oceans, fig. 5.13
2) Coastal Areas
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Characteristics:
* shallow areas with plenty light
* commonly higher energy
* abundance of life
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Examples:
coral reefs, mangrove forests
more common closer to equator
3) Estuaries & Marshes
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Characteristics:
very shallow areas under tidal influence
salinity changes with time
* brackish with lower salinity
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Examples:
tidal marshes
estuaries
barrier islands