Download The distribution of communities

Spatial distributions
The distribution
of
of
communities
communities
Part I: Community
structure and
gradients
Outline
Part I:
1. Basic definitions
2. Community function – energy
3. Spatial patterns
Part II:
1. Terrestrial classifications
2. Aquatic classifications
Basic definitions
Population
Group of inter-breeding individuals of a particular species
Metapopulation
set of local populations of a species that are linked by dispersal
among those population (e.g. source-sink)
Basic definitions
Community
• Assemblage of interacting organisms that share the
same habitat
• Boundaries – sharp or diffuse; somewhat arbitrary
– ecotone: transition zone between communities
Basic definitions
Ecosystem
• A set of abiotic and biotic components interacting
in a given environment
• Emphasizes function
Basic definitions
Biome
• A defined area of similar climate and vegetation type; it may
contain different taxa in different regions
• Defined by physiognomy, leaf
type, plant density
• Highlights the role of the
physical environment in
determining characteristics
of species assemblages
Biomes
Soil types
Climate
Soil type and climate are strong
determinants of global biome
distribution
Hierarchy
Community Organization: an
energetic perspective
How do species’ characteristics (niche) affect
community organization?
• Body size
• Trophic level
Body size :
1. Larger organisms require more energy
2. Smaller organisms require more energy per unit
3. Larger organisms generally have a greater capacity to
withstand prolonged stress (higher storage reserves)
Size influences scale of environment used by organism
Fine-scale heterogeneity
Landscape-scale heterogeneity
Based on these principles, can one defined geographic
area support more large or small species?
Community Organization
Trophic Level (how organisms acquire energy)
Primary producers – produce
biomass from inorganic compounds
(autotrophs or chemoautotrophs)
Herbivores/primary consumers –
organisms that eat a plant-based
diet (heterotrophs).
Carnivore/secondary consumers –
organisms that get nutrition from
animal tissues (heterotrophs)
Detritovores – consume detritus
(heterotophs)
Community Organization
Trophic Level (how organisms acquire energy)
0.1-10%
0.1-10%
0.1-10%
Community Organization
Trophic Level (how organisms acquire energy)
Less energy available to higher trophic levels
• Smaller carrying capacity
• Fewer species
• Larger and more generalized
Why are there rarely more than 5 trophic levels?
Spatial Patterns
Example: intertidal zone
Ecotone:
Zone of
transition
between two
habitats or
communities
Spatial Patterns
• Narrow ecotones can occur with abrupt environmental
change (e.g. lake shore)
– Species likely limited to one community
• Wide ecotones – often occur with gradual transitions
between more similar communities
– May support species from both communities
– May support ecotone specialists
– Can have high species richness
Ecotone specialists
Environmental gradient
Theoretical distributions of species along an environmental
gradient
Robert Whittaker 1975
Which figures show examples of competitive exclusion of
species? Why?
Robert Whittaker 1975
Which figures show examples of coevolved species? Why?
Robert Whittaker 1975
Spatial Patterns
Distribution of trees along an elevation gradient in the
Sierra Nevada (CA)
Biological interactions
or physical factors?
Yeaton 1981
So… what’s the typical pattern?
• Species typically replace each other gradually along smooth
environmental gradients
but
• When species with similar niches come into contact, sharp
boundaries can be observed due to competitive exclusion
• Sharp boundaries can also result from abrupt changes in
environmental conditions (i.e. lake shore)
Spatial distributions
of communities
Part II: Classifications
Classifying communities
• Difficult to classify communities into discrete units - do not
represent discrete associations of species in space/time
• But…humans like to classify
• Quantitative patterns - multivariate statistical techniques
used to quantify degree of similarity between two
communities
– Climate and soil have strong effect on types of plants in a region
Whittaker 1975
Terrestrial Vegetation Types
•
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•
•
•
•
•
Forest
Woodland
Shrubland
Scrub
Grassland
Desert
Tundra
Temperate Forest
• Evergreen and deciduous forests
• Dry & wet temperate forests
Tropical Forest
•Mainly broadleaf dominated
•Decidous dry forests
•Evergreen rainforests
Adaptation of species to low soil nutrients
• Buttressing of dominant plants
– Shallow roots stretch over surface, buttressing increases
stability and increase flow of dissolved nutrients
– Convergent architecture
Adaptation of species to variations in solar radiation
UV-shielding leaf cuticle on sun leaves and shade leaves (Krause
et al. 2003)
Adaptation of species to variations in solar radiation
Understory plants – large broad leaves
Epiphytes – plant that grows on another plant (non-parasite)
Woodland
Dominated by trees, but individuals are spaced and
do not form a continuous canopy
Example: Tropical Savannas (some savannas are classified as
shrublands)
Adaptation of species to drought
Grasses – rapid growth during wet periods, water and nutrient
storage in roots during dry periods
Taproots – enlarged straight tapering root that grows vertically
Trees store water in trunks, roots
Adaptation of species to fire
Perennial grasses – have rhizomes and can resprout (some have
argued this is an adaptation to herbivory)
Thick bark – protect vascular tissue from heat damage
Baobab (Adansonia)
Africa, Australia, Madagascar
Long-lived
Water storage in trunk
Tap root
Deciduous
Fire-resistant bark
Shrubland
Continuous layer of shrubs, up to several meters high
Example: Chaparral (sclerophyllous)
Adaptation of species to drought
Sclerophyllous – “sclero” = hard, phyll = leaf
Leaves – hard, thick, leathery, small (minimize moisture loss)
Chamise (Adenostoma fasciculatum)
Evergreen chaparral shrub native to California (2-12 ft tall)
Extensive root system (including taproot)
Fires generally occur frequently (e.g. 10-40 yrs)
Volatile secondary chemicals promote fire
Resprouts
Heat stimulates seed germination
Scrub
Shrubby individuals widely spaced
Example: Coastal sage scrub, coastal California
Adaptations to drought
Soft wax-covered leaves reduce moisture loss
Drought-deciduous leaves
Grassland
Dominated by grasses and forbs
Example: Temperate grasslands/Great Plains
Fire and grazing
Grasses grow from nodes (not tips)
Many species have rhizomes
Grazers can be selective – altering species community
Bison as a keystone species
N availability higher in grazed areas
Knapp et al 1991
Bison as a keystone species
Grass photosynthesis higher in grazed areas
Knapp et al 1991
Bison as a keystone species
grazed
ungrazed
Knapp et al 1991
Great Plains grasslands evolved under influence of
bison (Bison bison) but currently dominated by cattle
(Bos taurus)
• What are the differences in the grazing behaviors of
bison and cattle in a tall grass prairie? (Allred et al. 2011)
• Methods: Collared bison and cattle with GPS and
monitored locations
• Results:
– Cattle – preferred riparian zones
– Bison – not limited by proximity to water
• Implications: cattle in riparian areas may alter vegetation
(reduced veg cover, decreased productivity)
Desert
Most of the ground without vegetation; widely
spaced individuals
Example: Mohave Desert
Adaptations to heat and drought
Thick cuticle
Spines, hairs (reflect solar radiation)
Self-shade (pines, leaves)
Water storage
Shallow root system
Joshua tree (Yucca brevifolia)
Rapid initial growth
Deep, extensive root system
Narrow, waxy leaves
Tundra
Treeless biome under stressful environmental
conditions
Example: Alpine tundra
Adaptations to cold and dry
Mats or cushion growth form
Dwarf shrubs
Dark and hairy (absorb/trap heat)
Tap roots
Aquatic communities
Physical factors that affect aquatic organisms are
different than terrestrial systems
– Three-dimensional space
– Less temporal variation in temperature
– Variations in salinity, light, pressure, water movement,
nature of substrate
Aquatic communities
• Marine (oceanographers)– salinity varies ~ 35 ppt
• Freshwater (limnologists) – salinity usually < 0.5 ppt
Green Lakes Valley, CO
Marine community classification
• 1.37 billion cubic km in volume
• Temperature, light, pressure, substrate
• Marine classification – primarily based on water temp
Arctic
subarctic
Northern temperate
Northern sub-tropical
Tropical
Southern sub-tropical
Southern temperate
subantarctic
Antarctic
Marine community classification
Photic zone – “well lit”
Boundary is somewhat arbitrary,
but usually set where light is less
than 1-10% of incident solar
radiation.
Deepens with distance from coast
Important ecologically
Aphotic zone
Hydrothermal tube worms – symbiotic relationship
with chemosynthetic bacteria to produce organic
compounds in the Galapagos Rift
Marine community classification
Bathymetry – depth and
configuration of ocean
bottom
1. Intertidal
2. Neritic
3. Bathyal
4. Abyssal
Marine Organism Classification
Benthic – organisms
associated with a substrate
Pelagic – open water organisms
Freshwater Community Classification
Lotic – flowing water (streams, rivers)
Rapids/riffles – higher
water velocity (high oxygen,
rocky bottom)
Pools – deep, slow-moving
water (silty and poorly
oxygenated bottoms)
Clinger Mayfly larvae
Rainbow trout
Swimmer mayfly larvae
Freshwater Community Classification
Lentic – standing water (lakes, ponds)
Littoral – light penetrates to
bottom (rooted veg)
Limnetic – offshore water that
light penetrates for effective
photosynthesis (phytoplankton)
Profundal – beyond depth of
effective light penetration
Freshwater Community Classification
Lentic – standing water (lakes, ponds)
Eutrophic – ample/excessive
nutrients, often shallow, warmer,
lower oxygen content, subject to
algal blooms (high primary
productivity)
Oligotrophic – low nutrient content,
higher oxygen at depth (colder),
lower primary productivity
Eutrophication - Table Rock Lake, Missouri
Freshwater Communities
Rare community - Hypersaline Lake
Example: Great Salt Lake