Biogeo lec 5 the distribution of communities

THE DISTRIBUTION OFTHE DISTRIBUTION OF
COMMUNITIESCOMMUNITIES

Biogeographic PerspectivesBiogeographic Perspectives
• Ecological Communities - complex
associations of species
• To what extent are species distributed
together as interdependent communities
as opposed to being distributed essentially
independently of one another?

Biogeographic PerspectivesBiogeographic Perspectives
• Life zones, Ecoregions or Biomes -
specific kinds of animals and
microorganisms are associated with
specific vegetation formations associated
with particular climates

Communities and EcosystemsCommunities and Ecosystems
• Definitions –
– Community
– Community structure
– Community function
– Ecosystem
– Microcosm
– Biosphere

• Definitions -
• Community -consists of those species
that live together in the same place

• Community structure - static properties
including diversity, composition, and
biomass of species in a community

• Community function - all the dynamic
properties and activities that affect energy
flow and nutrient cycling

• Ecosystem - includes all the species
inhabiting a place as well as all the
physical features of the physical
environment

• Microcosms - small, relatively self-
contained ecosystems

• Biosphere - largest and only complete
ecosystem -> encompasses the entire
earth

Community Organization :Community Organization :
Energetic ConsiderationsEnergetic Considerations
• Basal metabolic rate - varies with body
mass

• Body mass - most important variable to
measure –> larger the organism the more
energy it requires for maintenance, growth
and reproduction

• Larger animals have greater reserves and
therefore greater potential to withstand
prolonged stresses such as starvation,
dehydration, and subfreezing
temperatures

• Smaller organisms require fewer
resources per individual than large ones,
use smaller areas, can be more
specialized, and still maintain population
densities high enough to avoid extinction

• Any geographic area contains a greater
number of small-bodied species than large
ones
AND
• Large organisms are constrained to have
broad geographic ranges

• Trophic Status - influences role in the
community structure

• Ecological Pyramids - successively
higher trophic levels tend to have less
than 10% the rate of energy uptake of the
level below them, and usually contain
proportionately lower biomass and fewer
individuals and species

• Carrying Capacity - (measured in units of
usable energy)

usable energy)
• –> lower for successively higher levels

usable energy)
• –> predictable characteristics that affect
ecological roles and geographic
distributions

usable energy)
ecological roles and geographic
distributions
• –> fewer species of carnivores than
herbivores

usable energy)
ecological roles
• and geographic distributions
• –> fewer species of carnivores than herbivores
• –> tend to feed on several species

usable energy)
ecological roles
• –> broad habitat requirements

• Carrying Capacity - (measured in units of usable
energy)
• –> predictable characteristics that affect ecological roles
• –> broad habitat requirements
• –> wide geographic distributions
• (Ex: Mountain lion, Puma concolor)

• Productivity varies greatly among different habitats
–> widespread highly productive habitats such as rain
forests and coral reefs have higher diversity of
specialized species
–> small, isolated areas (such as small islands) and
widespread unproductive habitats (such as boreal
forests and tundra) contain fewer specialized species
and more generalized species

Terrestrial BiomesTerrestrial Biomes
• Terrestrial communities are classified on
the basis of the structure of the vegetation

• Observed that similar climate regimes do tend to support
• structurally and functionally similar vegetation in disjunct
• areas throughout the world
• –> these similarities may result from convergence
• –> unrelated plant species in geographically isolated
• regions have evolved similar forms and similar
• ecological roles under similar selective pressures

• Six major forms of terrestrial vegetation
recognized:
• 1.) Forest
• 2.) Woodland
• 3.) Shrubland
• 4.) Grassland
• 5.) Scrub
• 6.) Desert

• 1.) Forest - a tree-dominated assemblage
with a fairly continuous canopy

• 2.) Woodland - a tree-dominated
assemblage in which individuals are
widely spaced, often with grassy areas or
low undergrowth between them bare

• 3.) Shrubland - a fairly continuous layer of
shrubs, up to several meters high

• 4.) Grassland - an assemblage
dominated by grasses and forbes

• 5.) Scrub - a mostly shrubby assemblage
in which individuals are discrete or widely
spaced

• 6.) Desert - an assemblage with very
sparse plant cover in which most of the
ground is bare

• Twelve common terrestrial biomes are
recognized
– correspond to the distribution of climatic
zones
– latitude and elevation reflect influence of local
climate and soil type

• Tropical rain forest - richest and most
productive
• covers approximately 6% of surface
• approximately 50% of species
• low elevations at tropical latitudes (10o
N to 10o
S)
• abundant rainfall (>180 cm annually)
• rainfall tends to be seasonal
• temperatures nearly uniform year-round (over
18o
C)

• Tropical rain forest (continued)–
• dominant plants are large evergreen trees that
form a closed canopy (30 to 50m)
• convergent morphology of trees (buttressed
bases, straight trunks, broad leaves with smooth
edges)
• also characterized by lianas (woody vines) and
epiphytes (orchids, ferns and New World
bromeliads)
• very little light reaches the forest floor which is
open and devoid of vegetation

Tropical rain forestTropical rain forest

• Tropical deciduous forest - occur in hot
lowlands outside the equatorial zone (between
10o
and 30o
latitude)
• rainfall is more seasonal
• dry season is more pronounced
• canopy is low and more open
• trees and shrub shed their leaves during the dry
season
• flowering and fruit maturation occurs during the
dry season

Tropical deciduous forestTropical deciduous forest
Synchronous blooming at the
start of the dry season
Madagascar
Puerto RicoCeiba trees in Ecuador

• Thorn woodland - tropical and subtropical
• hot semiarid lowlands
• small spiny or thorny shrubs and trees are the
dominant form
• Members of the genus Acacia are common on
all continents
• succulents such as cacti (Cataceae) in the New
World and convergent forms of Euphorbia
(Euphorbiaceae) in Africa are common
• often found on drier sites adjacent to tropical
deciduous forests

• Tropical savanna - dominated by a nearly
continuous layer of xerophytic grasses and
sedges and scattered with fire-resistant trees
and shrubs
• low to intermediate elevations at intertropical
latitudes (between 25o
N and 25o
S)
• one or two rainy seasons followed by intense
droughts
• weather patterns driven by seasonal shifts in the
Intertropical Convergence Zone

• Tropical savanna (continued) -
• annual rainfall varies from 30 to 160 cm
• 3 common factors:
• 1) seasonally intense precipitation
• 2) fire during the dry season
• 3) migratory or seasonal grazing
• intertropical Africa (most extensive savannas)
• support the most diverse community of large
grazing mammals in the world

Tropical SavannaTropical Savanna
Africa
Australia

• Desert - hot deserts and semideserts
occur around the world at low to
intermediate elevations
• --> especially in belts of dry climates (30o
to 40o
N and S)
• --> rain is seasonal and unpredictable
(often less than 25 cm per year)
• --> amount of rainfall is less than the
evaporative potential

• Sclerophyllous woodland (and
Chaparral) - mild temperate climates
• --> moderate winter precipitation
• --> long, usually hot, dry summers
• --> broad variety of xeric woodlands (Ex. -
Pinon-juniper, sandhill pine woodlands,
pine flatwoods)

ChaparralChaparral
King Sugar Bush
Californis Blue Oak, Iron Oak Aardwolf

• Sclerophyllous woodland (continued) -
• --> dominant plants have sclerophyllous
(hard, tough, evergreen) leaves
• --> can receive up to 100 cm rain per year
• --> areas that receive less than 60 cm of
rainfall per year have low, shrubby
vegetation -> Sclerophyllous scrubland
(Chaparral)

• Subtropical evergreen forest - also called
Oak-laurel forests or Montane forests
• --> common in subtropical mountains at
intermediate elevations
• --> China, Japan, disjunct areas of the Southern
Hemisphere and southeastern U.S.
• --> most dominant species are dicotyledons with
broad, sclerophyllous evergreen leaves (Ex. -
laurels, oaks, and magnolias)

• Temperate deciduous forest - temperate
latitudes
• --> also called Summer-green Deciduous
Forests
• --> variable in their structure and
composition across eastern North
America, western Europe, and parts of
eastern Asia

Temperate deciduous forestTemperate deciduous forest

• Temperate rain forest - uncommon, found
along the western coast of continents where
precipitation exceeds 150 cm per year and falls
during 10 months of the year
• --> cool temperatures predominate year round
• --> always above freezing
• --> epiphyte diversity is high consisting of
mosses, lichens, epiphyllous fungus and some
ferns
• --> renowned for world’s oldest and largest trees

Temperate rain forestTemperate rain forest

• Temperate grassland - situated geographically and
climatically between the deserts and the temperate
forests
• --> most extensive in the interior plains of the Northern
Hemisphere
• --> markedly seasonal, substantial annual variation in
temperature and rainfall
• --> vegetation dominated by grasses, sedges, and other
herbaceous plants (single stratum)
• --> tall grasslands to shortgrass plains
• --> vegetation growth is stimulated by fire and grazing

Temperate GrasslandTemperate Grassland

• Boreal forests – “swamp forest”, broad
band across northern North America,
Europe, and Asia in regions of cold
temperatures
• --> extends southward into temperate
latitudes at high elevations (i.e., into
southern Mexico)
• --> dominated by a few species of
coniferous trees (Ex. - spruce and firs)

• Boreal forests (continued) -
• --> decomposition rates are slow because of
cool temperatures and waterlogged soils
• --> results in the accumulation of peat and humic
acids
• --> soil nutrients unavailable for plant growth
• --> acidic soils and cool temperatures limit
diversity and productivity

• Tundra - treeless biome found between
the boreal forests and the polar ice caps
• --> also at high elevations on tall
mountains (Alpine tundra)
• --> temperatures below freezing for at
least 7 months of the year
• --> precipitation less than many deserts
• --> soils more nutrient poor than boreal
forests environment

• Tundra (continued) -
• --> single, dense stratum of vegetation
• --> high productivity during short growing
season
• --> heavily grazed by migratory mammals
such caribou (Rangifer tarandius), muskox
(Ovibus moshatus) and Dall sheep (Ovis
dalli)
• --> fragile environment

Biogeo lec 5 the distribution of communities

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