Biome : Major Ecological Unit with Similar Plant and Animal Communities

Global Biomes

I. Definition

“biome” : major ecological unit with similar plant and animal communities.

II. Relative Net Primary Productivity

III. Three BiomesA. Desert Biome

Associated with dry climate zones: dry tropical, dry subtropical , dry midlatitude

Where are deserts? Subtropical Highs, Rain shadows, Interiors of continents

Characteristics:

1. low annual precipitation (Cold or Hot)

2. lowest net primary productivity of all biomes (not many plants produced)

3. Plants and animals have adapted strategies: xerophytic

Xerophytic plant strategies in the desert :

a) minimize stomatal water loss by having:

thick leaves

Spines (modified leaves)

waxy cuticles

leaves that fold up during the hot part of the day

(stomata are pores on leaves through which water is lost in transpiration)

b)ephemeral plants (annuals)

complete the entire cycle in short period of time after rain

Some seeds have coatings that dissolve ONLY when the ground is wet.

(Ocotillo is an example of a desert plant that sheds leaves in dry periods; replaces leaves in wet period)

c) Water storage tissue (cacti)

d) Long roots to reach water table (phreatophytes) “wet toes”

e.g. mesquite (80 ft. deep roots

e) hydraulic lift. (example: Creosote bush) :

During day: water is absorbed through roots; at night: plant’s deep roots take in so much water, can leave excess in dry surface soil so that the next day, the plant can absorb the excess)

f) Protection from predators (e.g. spines)

Animal strategies in the Desert :

a)Burrowing: examples: Rats, fox, ground squirrels

b) Nocturnal

c) cold-blooded animals take advantage of warm Rocks that collect and radiate warmth: Snakes, scorpions, lizards

(An example of a desert animal is Kangaroo rats: live in dens; recycle moisture from breath; Specialized kidneys extract moisture from urine; Get moisture from dry seeds)

B. Grassland Biome

Vegetation: Perennial grasses and other herbaceous plants; Very few trees and shrubs

Prairie (tall grass) and Steppe (short grass)

1) Long grass grassland (“prairie”)

Subhumid climate: relatively dry (24-39” annual rain); long, cool winter

grasses: 0.6 - 1.2 meters in height

2) short grass grassland (“steppe”)

Semiarid climate: dry (10-20” rain)

grass < 0.5 meters

Grasses are extremely tolerantto grazing and firebecause mode of growth is underground.

In fact, Fire is necessary for grasslands:

fire destroys woody plants, but grasses survive

If fires are suppressed: woody plants invade

Grassland animals:

Bottom of food chain: grasses and forbs

(Extensive root mats of perennial grasses provide plenty of compost for decomposers).

Herbivores: Grasshoppers, locusts, voles, birds, prairie dogs, jack, rabbits, bison

Carnivores:Snakes, skinks, coyotes, badgers, fox

Most of the native prairie grasslands in the world have been replaced by agriculture (grain and pasture) :

C. Tundra biome

Arctic Tundra(high latitudes) and Alpine Tundra (high altitudes)

Tundra Characteristics:

1)Short growing season (< 50 days between frosts)

2) Permafrost (permanently frozen ground)

The active layeris the part above the frozen soil that thaws during the growing season, but it does not drain because beneath it is frozen ground.

3) low precipitation

4) low productivity (second lowest net primary productivity)

Tundra vegetation:

1) treeless!

2) mosses, lichens, hardy grasses, sedges, dwarf shrubs, herbs

3) Low diversity of species:

Only 3%of earth’s species are adapted to severe cold !

Plant and animal strategies in the tundra: avoidance!

complete life cycle rapidly

short food chain

migrate (animals only!) out of tundra in winter, back into tundra in summer

Bottom of tundra food chain:Mosses and lichens, Marsh grass, Cotton grass

Hordes of insects arrive when active layer thawsBlackflies, mosquitoes

Herbivores : Caribou ()Travel in large herds, migrate into tundra in summer

Others: Musk ox, Ptarmigan, Arctic hare, Grouse, Lemming

Carnivores: Ermine, arctic fox, polar bear, wolves, snowy owls

No hibernation:Animals cannot hibernate here due to short summer

Some burrow into snow in winter (lemming) or have frozen larders (fox)

Many migrate to tundra in summer to take advantage of growing season

Few year-round residents (arctic fox, musk ox)