Ecosystem:All the organisms in a community plus abiotic factors
-ecosystems are transformers of energy & processors of matter
Trophic levels
-feeding relationships
-start with energy from the sun, captured by plants(1st level of all food chains)
-food chains usually go up only 4 or 5 levels (inefficiency of energy transfer)
-all levels connect to decomposers
Ecological pyramid
-Loss of energy between levels of food chain (can feed fewer animals in each level)
Food chains are linked together into food webs
Water cycle
abiotic reservoir: surface & atmospheric water
enter food chain: precipitation & plant uptake
Recycle: transpiration (Deforestation breaks the water cycle, groundwater is not transpired to
the atmosphere, so precipitation is not created)
return to abiotic: evaporation & runoff
Carbon Cycle
abiotic reservoir:CO2 in atmosphere
enter food chain: photosynthesis = carbon fixation in Calvin cycle
return to abiotic: respiration & combustion
Phosphorus cycle
abiotic reservoir:rocks, minerals, soil
enter food chain:-erosion releases & soluble phosphate uptake by plants
Recycle: decomposing bacteria & fungi
return to abiotic:loss to ocean sediment
Nitrogen cycle
abiotic reservoir:N in atmosphere
enter food chain: nitrogen fixation by soil & aquatic bacteria
Recycle: decomposing & nitrifying bacteria
return to abiotic: denitrifying bacteria
Community: all the organisms that live together in a place (interactions)
Community Ecology: study of interactions among all populations in a common environment
An organism’s niche is its ecological role (habitat = address vs. niche = job)
Competitive Exclusion: No two similar species can occupy the same niche at the same time
-Resource partitioning: Reduce competition through microhabitats
Interspecific interactions
-Symbiotic interactions
-competition (-/-):compete for limited resource & competitive exclusion
-predation / parasitism (-/+)
-mutualism (+/+) Ex.lichens (algae & fungus)
-commensalism (+/0) Ex.barnacles attached to whale
Predation drives evolution
Predators adaptations: locate & subdue prey
Prey adaptations: elude & defend
Anti-predator adaptations
-Hide from predators (avoid detection)
- camouflage (cryptic coloration)
-Warn predators
-advertise how undesirable you are as prey
-aposematic coloration (apo = away & sematic = sign/meaning)
-Common warning coloration: Aposematic species come to resemble each other
-Batesian mimicry (palatable or harmless species mimics a harmful model)
-Mullerian mimicry (two or more protected species look like each other)
Coevolution in Community
-Predator-prey relationships
-Parasite-host relationships
-Flowers & pollinators
Characterizing a community
Community structure:
-species diversity (how many different species)
-composition
-dominant species
-most abundant species or highest biomass (total weight)
-keystone species
-changes over time
-succession
Species diversity (greater diversity = greater stability)
Greater biodiversity offers:
-more food resources
-more habitats
-more resilience in face of environmental change
“Monoculture”
Keystone species
Influential ecological role
-exert important regulating effect on other species in community
-keystone species increases diversity in habitat
Ecological succession:Sequence of community changes
-transition in species composition over time ( years or decades )
-usually after a disturbance (as natural cycle: Disturbances are often necessary for community
development & survival)
Primary succession:Begins with virtually lifeless area without soil,then…bacteria,lichens &
mosses,grasses,shrubs,trees
Secondary succession:Existing community cleared,but base soil is still intact
What causes succession?
-Tolerance
-early species are weedy r-selected
-tolerant of harsh conditions
-Facilitation & Inhibition
-early species facilitate habitat change
-change soil pH
-change soil fertility
-change light levels
-allows other species to out-compete
Climax forest: Plant community dominated by tree (representing final stage of natural
succession for specific location)
-stable plant community:(remains essentially unchanged in species composition as long as
site remains undisturbed) Ex.birch, beech, maple,hemlock,oak, hickory, pine
-The species mix of climax forest is dependent on the abiotic factors of region (solar
energy levels,temperature,rainfall,fertility & depth of soil)
-Fire climax species: adaptations to survive and reproduce in areas that experience
frequent fires
A population is a group of individuals of the same species that live in the same area
Density:The number of individuals per unit area/volume (Example: 47 elephants/km2)
Dispersion:The pattern of spacing among individuals in a population
-Uniform:
-Environmental conditions are uniform
-Causes:COMPETITION or antagonism between organisms
-Clumping:( most common)
-Reproductive patterns favor clumping
-Social behaviors lead to clumping
-Optimal density is usually intermediate (medium)
-Random: (rarely happens)
-No competition & No tendency to group/clump
-Conditions are uniform
There are 3 major factors that influence population size:
1. the number of births
2. the number of deaths
3. the number of individuals that enter or leave a population
- immigration:individuals entering an existing population
- emigration:individuals leaving an existing population
Reproductive Episodes:
Clutch size:Number of offspring produced at each reproductive episode
Semelparity:A life history in which an organism spends most of its energy in growth and
development,expend their energy in one large reproductive effort, and then die ( Ex.Many
insects, annual plants, salmon, etc.)
Iteroparity:A life history pattern in which organisms produce fewer offspring at a time over a
span of many seasons (Example: humans, panda bears, etc.)
Estimating Population Size:The mark-recapture method can be used to estimate the size of a
population(Capture, mark, release,Recapture and count)
Equation:
N = Number marked x Total catch 2nd time
Number of marked recaptures
Exponential Growth:
-Occurs in ideal conditions with unlimited resources (J shaped curve)
-Exponential growth cannot continue indefinitely,It is characteristic of populations who are
entering a new environment OR those whose numbers are rebounding from a catastrophic
events.
r- strategists
-Grow exponentially when environmental conditions allow; when conditions worsen, population
size plummets.(Bacteria, some plants, insects)
-Short life span
-Reproduce early in life
-Many offspring/large clutch size
-Usually small in size
-Little or no parental care
Logistic Growth:(Characterized by an S-shaped curve)
-Pattern of population growth which takes into account the effect of population density on
population growth
-Occurs when resources become more scarce
Carrying capacity (K):
-The maximum number of individuals that a particular environment can support over a long
period of time
-Determined by such limiting factors as crowding and food resources
Graph levels off at carrying capacity:
-K-selected populations (equilibrial populations) live near or at the carrying capacity
K-strategists:(Density stays near carrying capacity.)
-Large, slow growing organisms
-Small population sizes
-Long life span; slow maturation
-Few young/small clutch size
-Reproduce late in life
-Parental care
-Most large mammals; endangered species
Limiting Factors:There are a number of factors that limit the size of populations:
-Density-dependent limiting factors
-The effect of density-dependent limiting factors intensifies as the population increases
-Intraspecific competition (Food, space, etc.)
-Predation
-Disease (if caused by pathogen/contagious)
-Density-independent limiting factors
-The occurrence and severity of density-independent limiting factors are unrelated to population
size
-Climate
-Disease (if not caused by pathogen/not contagious)
-Pollution
Density-dependent and density-independent limiting factors often work together to regulate
the size of a population
-Deer in snowy winter
-Starve from lack of food (DDLF)
-Severity of winter/depth of snow determines access to food (DILF)
Type I- live to old age
& die (most large
mammals)
Type II- constant
mortality rate (rodents,
lizards, hydra)
Type III- high mortality
at young age, but if
they survive they live a
long life.
Human Population Growth
-Implications of exponential human population growth:
-Lack of food supplies
-Lack of space
-Lack of natural resources (metals, fossil fuels, etc)
-Lack of sites for waste disposal
innate behaviors:
-automatic, fixed, “built-in”, no “learning curve”
-despite different environments,all individuals exhibit the behavior
(ex. early survival, reproduction, kinesis, taxis）
learned behaviors：
-modified by experience
-variable, changeable
-flexible with a complex & changing environment