Species Interactions
and Biomes
Chapter 4
After THIS LECTURE, You will be able to:
Compare and contrast the major types of species interactions
Characterize feeding relationships and energy flow, using them to construct
trophic levels and food webs
Distinguish characteristics of a keystone species
Characterize succession and notions of community change
Perceive and predict the potential impacts of invasive species in communities
Explain the goals and methods of restoration ecology
Describe the terrestrial biomes of the world
Central Case Study: Black and White and Spread All Over
In 1988, ballast water discharged from a ship accidentally released zebra
mussels into Lake St. Clair
By 2010, they had spread to 30 states
They cause millions of dollars of property damage each year
TYPES OF Species interactions
Competition occurs with limited resources
Competition happens when multiple organisms seek the same limited resource
Intraspecific competition occurs between members of the same species
Interspecific competition occurs between members of different species
Leads to competitive exclusion or species coexistence
Resource partitioning
Resource partitioning occurs when competing species coexist by specializing
By using different resources (small vs. large seeds)
Or using shared resources differently (active during day vs. night)
An exploitative interaction: predation
Predation is the process by which individuals of one species (predators)
capture, kill, and consume individuals of another species (prey)
Predation can drive population dynamics
Increased prey populations increase food for predators
Increased predator populations decrease prey
Decreased predator populations increase prey populations
Predation has evolutionary ramifications - COEVOLUTION
Natural selection leads to evolution of adaptations that make predators better
hunters and prey better at avoiding or escaping predation
“Evolutionary Arms Race”
Prey develop defenses against being eaten
Chemical DEFENSES
Camouflage
Warning coloration
MULLERIAN Mimicry
Two unpalatable species evolve to look alike
BATESIAN Mimicry
Harmless species evolve characteristics that mimic unpalatable or poisonous
species
An exploitative interaction: parasitism
Parasitism is a relationship in which one organism (parasite) depends on
another (host)
ParaSITOIDS KILL THEIR HOSTS
An exploitative interaction: herbivory
Herbivory occurs when animals feed on the tissues of plants
Defenses against herbivory include:
Chemicals: toxic or distasteful
Thorns, spines, or irritating hairs
Herbivores may overcome these defenses
Mutualists help one another
Two or more species benefit from their interactions
Symbiosis is a relationship in which the organisms live in close physical contact
(mutualism and parasitism)
PLANT/PolLINATOR
PLANT/Mycorrhizae
CORAL/ALGAE (ZOOXANTHELLAE)
Acacia and ants
Energy passes among trophic levels
One of the most important species interactions
Who eats whom?
Matter and energy move through the community
Trophic levels explain where an organism is in the feeding hierarchy
Ecological pyramids
Due to Second Law of Thermodynamics, food chains often form a pyramid
Large amount of energy, numbers and biomass at bottom of the food chain
Pyramids of energy, biomass, and numbers
Food webs show relationships & energy flow
Food chain is a linear series of feeding relationships
Food web is an intricate diagram of feeding relationships and energy flow
among organisms
Some organisms play big roles
A keystone species has a strong or wide-reaching impact, which is far out of
proportion to its abundance
Keystone species
Species can change communities
Trophic cascade is when predators at high trophic levels indirectly promote
populations at low trophic levels
Wolves promote plant populations
Ecosystem engineers physically modify the environment
Communities respond to disturbances
Communities experience many types of disturbance, natural and
anthropogenic
Resistance: a community resists change and remains stable despite the
disturbance
Resilience: a community changes in response to a disturbance, but later
returns to its original state
Or, a disturbed community may never return to its original state
Primary succession
Succession is the predictable series of changes in a community
Primary succession occurs when site has no recent life
Pioneer species are the first species to arrive in a primary succession area
Secondary succession
Secondary succession occurs when a disturbance has removed much, but not
all, of the biotic community
Fires, hurricanes, logging, farming
Invasive species threaten stability
Invasive species is a non-native species that spreads widely and become
dominant in a community
Introduced deliberately or accidentally
Growth-limiting factors (predators, disease, competitors, etc.) are absent
Major ecological effects
Controlling invasive species
Techniques to control invasive species include:
Removing them manually
Applying toxic chemicals
Drying them out, depriving them of oxygen
Introducing predators or diseases
Stressing them with heat, sound, electricity, carbon dioxide, or ultraviolet light
Control and eradication are hard and expensive
Prevention, rather than control, is the best policy
Altered communities can be restored
Humans have dramatically changed ecological systems
Severely degraded systems cease to function
Restoration ecology is the science of restoring an area to an earlier (usually
presettlement) condition
Widely separated regions share similarities
Biomes are areas sharing similar climate, topographic and soil conditions, and
roughly comparable communities
Abiotic factors influence biome locations
The type of biome depends on temperature and precipitation
Climatograph is a climate diagram showing an area’s mean monthly
temperature and precipitation
Desert
Minimal precipitation
Temperatures vary widely daily and seasonally
Adaptations for water conservation and resistance to heat
Animals tend to be nocturnal and nomadic
Plants have thick skins, spines, whitish in color
Overgrazing a threat
Sensitive to disturbance
Hot and COLD DESERTS
Temperate grasslands
More temperature difference between winter and summer
Lower precipitation supports grasses, but not trees
Also called steppe or prairie
Once widespread, but has been converted to agriculture
Overgrazing occurs
Fires and grazing important
Savanna
Grassland interspersed with trees
Precipitation occurs during the rainy season
Tundra
Minimal rain
Permafrost keeps moisture unavailable
Alpine tundra is found on mountaintops
Very short growing season, with cold harsh winters
Most animals migrate south or downhill in winter
Low biological productivity and low diversity
Treeless
Threatened by oil/gas drilling and climate change
ALPINE AND ARTIC TUNDRA
Boreal forest
Evergreen tree species
Cool and dry climate
Nutrient poor, acidic soil
Taiga describes northernmost part of boreal forest that has fewer trees
Temperate rainforest
Heavy rainfall and mild temperatures
Coniferous trees
Erosion and landslides affect the fertile soil
Most old-growth is gone as a result of logging
Temperate rain forest
Temperate deciduous forest
Deciduous trees lose their broad leaves each fall
Fertile soils
Rich variation of tree species
Logging impacts
Tropical rainforest
Year-round rain and warm temperatures
Dark and damp
Lush vegetation
Diverse species
Very poor, acidic soils as nutrients are in living organisms
Logging and agriculture threaten ecosystems
Tropical dry forest
Also called tropical deciduous forest or tropical seasonal forest
Wet and dry seasons
Warm temperatures
Much of it converted to other uses
Chaparral OR MEDITeRRANEAN
A regional biome
Densely thicketed, evergreen shrubs
Mild, wet winters and warm, dry summers
Fire important
Mediterranean