Lecture 13 - Ecology Flashcards
Definition of ecology
scientific investigation of interactions among organisms and between organisms and their physical environment
generates knowledge about the complex interrelations in the natural world
- not environmentalism
- even small organisms have an effect
Dung Beetle example
- settlers from britain btought cattle to australia
- didnt bring right kind of dung beetle
- normally consume and break down dun
- without this, pastures become unusable for grazing
- bush fly population exploded
- parasitic infections in cattle increased
- imported correct dung beetle to solve problem
Climate
- determines the kind of organisms that can survive and reproduce in a particular place
- energy from sun is main determinant
Climate vs weather
weather: the short term state of atmospheric conditions at a particular place in time
climate: average atmospheric conditions and their extent of variation at a particular place over a long span of time
Solar energy and latitude
Equator:
- sunlight is perpendicular
- most energy
Poles:
- at an angle
- less intense
- higher latitudes experience greater variation in day length and angle of solar energy over the course of a year, leading to more seasonal variation in temp
Solar energy and Air circulation –> rainfall
- when air is warmed, it expands and rises
- as it rises it cools
- cool air cannot hold as much moisture as warm air
- cooling air releases moisture in the form of precipitation
- warmest at equator, most precipitation in rain forests - as air rises it is replaced by air from the north and south
- draws in air from the region around 30 degrees latitude - cool dry air descends into the region
- earths great deserts - at about 60 degrees latitude air rises again
–> creates wind patterns
Wind pattern
- cyclic movement of air masses rising and falling contribute to wind (north and south)
- roatation of earth on its axis also contributes to prevailing winds (winds deflected est or west)
- velocity of rotation is fastest at the equator, where the diameter is the greatest
- air mass moving towards the equator is rotating slower than the earth beneath it - wind blows to the west
(ex: tradewinds columbus used to sail to americas) - air mass moving towards the poles is rotating faster than the earth beneath it - wind blows to the east
(ex: westerlies which cause most us weather to move from west to east)
Ocean currents
Air circulation patterns drive currents:
- ex: westerlies and tradewinds blow in opposite directions
- continents prevent water from circling the globe
- water is pushed together at equator, where it moves westward until it reaches land and then divides
- clockwise in N. hemisphere, counter-clockwise in S. hemisphere
Currents affect climate:
- poleward movement of water that has warmed in the tropics transfers large amounts of heat to higher latitudes
- ex: gulf stream to europe
Role of local topography
- major topographic features such as mountains or large lakes have regional effects on temperature and precipitation
- when winds bring air masses into contact w/mountain range, air rises to pass over
- -> cools as it rises
- -> clouds frequently form on windward side and release rain and snow
On leeward side (opposite from winds), now dry air descends, warms, and picks up moisture
- -> little rain and arid condition
- -> rain shadow
Biomes
Combination of sun intensity, wind patterns, ocean currents –> many distinct environments
Environment characterized by:
- climactic and geographic attributes
- ecologically similar organisms (especially plants)
animals in similar biomes often share many physiological, morphological and behavioral adaptatons
distribution determined largely by temperature and rainfall
Tundra
Winter is cold and long, summer is cool and short. Little precipitation
Arctic: Near poles
- vegetation is low-growing perennial plants
- underlain by permafrost (soil with permanently frozen water)
- usually wet cause water cannot drain through permafrost
Alpine: High elevations
- not underlain by permafrost
- low growing shrubs and grasses
*most animals either summer migrants or dormant for much of the year, thick fur
Boreal and temperate evergreen forest
Winter is cold, dry and long, summer is mild and humid
- latitudes below arctic tundra and elevations below alpine tundra
- short summer favors trees with evergreen leaves that are ready to photosynthesize as soon as temperatures warm
- conifer trees and shrubs
- animals: moose, hares, rodents and birds that eat conifer seeds
temperate and deciduous forest
Winter is cold and snowy, summer is warm and moist
- many types of deciduous trees (lose leaves in winter, shrub layer
- temperatures fluctuate dramatically between summer and winter
- precipitation is evenly distributed through the year
- many types of animals
- some migrate in winter, other have massive fat stores and hibernate
temperate grasslands
- Relatively dry most of the year, winter cold and dry, summer is warm and wetter
- vegetation - mostly grasses, few trees
- animals - grazing herds
- plants adapted to grazing and fire (energy underground and sprout quickly after being burned or grazed)
- topsoil is usually righ and deep, good for crops especially corn and wheat
hot desert
- around 30 latitude
- Hot and dry: winter is very warm and dry, summer is very hot and dry (but slightly less dry)
- plants are structured to conserve water
- small animals are inactive during hottest part of the day- can burrow underground
- mammals have physiological conditions for conserving water (ex: high concentrated urine)
- -> many require no water beyond what they can extract from carbohydrates in food
cold desert
high and dry: mid to high latitudes (rain shadows of mountain ranges)
- seasonal changes in temperature are large
- winter is cold and very dry
- summer is much warmer, still dry
- few species of low-growing shrubs
- animals tend to be seed-eating birds, ants, rodents
- many animals burrow
chaparral
Warm (mild), dry summers and wet, cool (mild) winters
- found in mid-latitudes on western sides of continent where cool ocean currents flow offshore
- low growing shrubs and trees with tough evergreen leaves that conserve water
- many small rodents
- animals burrow to avoid mid-day heat and forage at night
Tropical savannah
Winter is mild and dry, summer is very wet but not much warmer than winter (mild temps)
- latitudes in between the hot deserts and the equator
- many plants similar to those found in hot deserts
- spiny shrubs and small trees
- expanses of grasses with scattered individual trees
- acacia tree common
- herds of grazing and browsing mammals and then large carnivores that prey on them
- if not grazed, browsed or burned, reverts to dense thorn forest
tropical deciduous forest
Winter is very hot and dry, summer very hot and wet
- as length of rainy season increases closer to equator, tropical deciduous forest replaces thorn forest
- taller trees and fewer succulents
- support a much greater number of plant and animal species
- “nectar corridor” = many flowering plants
- fertile soil for the tropics area
tropical evergreen forest
rainforest- warm and rainy all year
- near equator
- most species rich of all biomes
- forests, cover <2% of earths surface, but are home to over half of all known species
Population Ecology
vs
Community Ecology
Regulation of a population of one species
vs
How populations of different species interact with and influence one another
Population
- individuals of a species that interact with one another within a given area at a particular time
- groups of individuals that interact in space in time have characteristics that individuals do not
- have a characteristic dispersion pattern (spatial distribution)
- have a characteristic age structure
Population density
- the number of individuals per unit of area or volume
- births and immigration vs deaths and emigration
Population dynamics
- the patterns and processes of change in populations
Measuring population densities
- in most species it is impossible to accurately count all individuals
- pop per unit is estimated by samples
SEDENTARY organisms
- count the individuals in a sample of representative locations
- extrapolate the counts to the entire geographic range of populations
MOBILE organisms
- capture, mark, release
- allow time for marked individuals ot mixed with unmarked
- capture another sample
- determine what proportion in new sample has the mark
Life Tables
Track demographic events and rate at which they occur in a population
births, deaths, immigration, emigration
Cohort life table: Survivorship
- start with a group of individuals born at the same time and track their deaths until no individuals from that cohort remain alive
Calculate the survivorhip and mortality:
Survivorship: proportion of the original coort that survived to reach that age class
mortality: proportion of individuals in each class that die before reaching the next age class
Cohort life table: Fecundity
- cohort life tables also used to track the degree to which individuals in different age categories contribute to reproduction
- track the number of offspring produced by each female during each time period
Fecundity: the average number of offspring per female
- allows scientists to estimate a populations potential for growth
- vary greatly among species
- # of offspring they can reproduce
- timing of reproduction
Survivorship Curve
- mortality data from a life table can be used to plot a survivorship curve
- classified by the pattern the population displays
x= age y= survivorship
Types of survivorship curves
Type I: Physiological
- organisms that experience high overall survivorship through adulthood (such as humans)
- parental care and low fecundity
Type II: ecological
- organisms faced with a constraint risk of mortality at all ages (such as birds)
Type III:
- organisms that experience low juvenile survivorship (such as insects and annual plants)
- many offspring but little or no parental care
Exponential growth
as the number of individuals in a population increases, the number of new individuals added per unit of time accelerates
conditions for populations to grow exponentially
*short period of time
- unlimited resources
- no predators
- favorable climate
Flies and exponential growth
- estimated that a pair of flies beginning to reproduce on april 15 could produce 5 trillion offspring in 5 months
- do not see the explosion expected
- factors at work limit their growth
Population crash
- puts an end to exponential growth
Exponential growth and limitation
- no real population can maintain exponential growth for very long
- as population increases in density, resources it requires (food, shelter..) become depleted
- in absence of resources available to sustain more individuals
BIRTH RATES DROP AND DEATH RATES RISE
Carrying capacity (K)
the finite number of individuals that a given environment has enough resources to support
Logistic growth
- growth of a population slows down as its density approaches its environment carrying capacity
- population stops growing exponentially before it reaches the carrying capacity
- forms a S-shaped curve
- plateau = carrying capacity
Factors that limit population growth
Density dependent
Density-independent
density dependent
food supply
- as a population increases, amount of food available to each individual decreases
- poor nutrition will increase death rate and decrease birth rate
predators
- attracted to areas with high density of prey
- able to capture a larger proportion of prey - death rates rise
pathogens
- spread more easily in dense populations - deathr ates rise
density independent
extreme temperatures
natural disasters
- (ex hurricane blows down trees)
R- strategists
- species who live in unpredictable habitats
- high fecundity (reproduce once and a large number of offspring)
- make the most of rare opportunities to reproduce
K- strategists
- species who live in predictable habitats
- have a high probability of reproductive success
- low fecundity
(long lived, reproduce several times with pair bonded mate, small number of offspring with high prob of surviving) - persist at or near carrying capacity
- more specialized to resource use and less tolerant of variation
Harvesting species
Population management
- fast reproducing species, birth rates and growth rates are density dependent
- -> if a pop is far enough below carrying capacity, birth rates are high
- small numbers of reproductive-aged females can produce sufficient numbers of eggs to maintain the population
Over-harvesting
- so many individuals are harvested that the number of reproductive adults cannot maintain the population
- rapidly reproducing species (ex fish) can often rebound if over-harvesting is stopped
- slowly reproducing species (ec whales) have much more difficult time recovering
Controlling pest species
- lower carrying capacity
- just killing some off will only increase their reproductive rates
- ex: limit food supply (make garbage unavailable for rates)
- ex: introduce natural predators (introduce ladybug and fly to eat insects)
- sometimes predators become the pests
- ex: cane toads in australia
- -> introduced to control cane beetles in sugarcane fields
- -> cannot reach the cane beetles to eat them
- -> but no predators and are poisonous to other species
- -> out-compete native amphibians for resources
Exponential growth of humans
- increased carrying capacity
- for thousands of years, carrying capacity was low due to relative inefficiency with which humans could obtain food and water
- advances have increased carrying capacity
–> developments:
social systems and communication
domestication of plants and animals
technological advances to increase crop and livestock yields advances in sanitation and living conditions
increased proficiency at managing species
took 10,000 years for pop to reach 1 billion
125 years later we are at 7 billion
US, baby boomer
developing countries, booming now
Community Ecology
How populations of different species interact with and influence one another
Antagonistic interactions
- one species benefits while other is harmed
(+/-)
Predation
- individual of one species kills and consumes individuals of another
Herbivory
- individuals of one species consumes a plant
Parasitism
- one species consumes only certain tissues in a host of another species without necessarily killing those hosts
Mutualism
(+/+)
- interaction benefits both species
Ex: ant cultivates fungi and feeds them with leaves, fungi serves as food for ants
Ex: birds eat parasitic ticks off buffalo’s backs
Competition
(-/-)
- two or more sepcies use the same resource
- outcome depends on resource availability
Ex:
- two predators that depend on same prey
- two herbivores that eat same plant
- two plants in the same location both need sunlight
Commensalism
(+/0)
- one participant benefits, other is unaffected
- usually focused on one species feeding in, on, or around another that makes its own food more accessible
ex: brown headed cow bird
- follows herd of grazing cattle
- forages on insects flushed from vegetation by cow’s hooves and teeth
Amensalism
(-/0)
- one participant in unaffected while the other is harmed
- tend to be more random
ex: herd of elephants moving through forest crushes insects and plants
Boundaries between categories are unclear
Ex: Clownfish and sea anenome
- sea anenomes sting and eat many fish, some species (such as clownfish) are unaffected
- clownfish hides in sea anenome
commensalism?
- fish are protected from predators at no harm to anenome
mutualism?
- fish also provide nutrients
competition?
- fish occasionally steals anenome’s prey
Evolutionary adaptations from relationships:
- predator prey adaptations
- mutualistic adaptations
- competition adaptations
Reciprocal adaptation
(co-evolution)
- adaptations within one species may lead to evolution of an adaptation in a species that it interact with
Ex: predator can become swifter, more powerful, more efficient
-> prey becomes swifter, tougher, less conspicuous, etc
Co-evolutionary arms race
- series of reciprocal adaptations back and forth between two species
Adaptations of predators
Balance cost of pursuing, subduing and handling prey against energetic return from consuming it
- most are larger that their prey, use strength or swiftness to capture prey
- a few are smaller, rely on strategies that increase efficiency (spiders with web)
Adaptations of prey
Many different defenses against predators
- running away
- morphological defense (tough skin, shells, spines)
- camouflage (match background, resemble objects predator considers inedible)
- chemical defenses
chemical defenses
widely used by species that are small, weak, sessile, unprotected
- Aposematism
- mimicry systems
aposematism
- prey that defend themselves with toxicity advertise it
- warning coloration
- bright colors with striking patterns
- predators learn to recognize and avoid toxic species
- often tough enough to survive a brief encounter with a predator
mimicry systems
- nontoxic species resemble a toxic one
- benefits from the avoidance behavior learned by the predator
- number of aposematic species converge on a common color pattern
- all benefit from providing a stronger recognition signal to predators
mutualistic interactions and adaptations
- mutually beneficial interactions between species can result in reciprocal adaptations too
- often arise in environments where resources are in short supply
- involve exchange of food, housing or defense
- sometimes more sessile (plants) organisms for mating or dispersal
- reciprocal adaptations are most likely to arise if an increase in dependency on a partner provides an increase in benefits from the interaction
- if increased dependence provides no advantage, may evolve into parasites
examples of mutualistic adaptations
Plants and pollinators
- pollen or nectar that attracts the pollinator
- location, size of anthers and stigma
- depth and width of the flower and timing of flowering
- floral characteristics and patterns that attract specific pollinators
Fruits and seed transport
- animals eat appealing fruits (fruits evolved to be appealing, must be appealing only when seeds ready for dispersal)
- seeds pass through digestive tract and are dispersed (must not be harmed by digestive tract
Exchange of food and housing for defense
- evolve structures for housing or feeding insects, fungi, etc
- acadia tree has special hollow thorns in which ants build nests
- tree also produces nectar whose only purpose is to feed ants
- ants protect plant against herbivores and competitors
exchange of food and housing for defense
competitive exclusion
if one species can prevent all members of another species form utilizing a resource, the inferior competitor may go extinct
resource partitioning
- selective pressures change the way a species uses its limiting resource so the two coexist
exploit different niches
Ex: two types of barnacles
ecological community
A group of species that coexists and interact within a defined area
can rang ein size and scope
can be defined by distribution of energy and biomass within it
biomass: total weight of all organisms in a given group
can vary greatly in species richness (number of species they contain)
certain general principles are true of communities
Primary producers
how energy enters the system
- sunlight is ultimate source of energy for most of the earth’s communities
- primary producers: use photosynthesis to convert sunlight to chemical energy
- autotrophs - capable of feeding themselves via sunlight, all species that are NOT primary producers are heterotrophs
- make energy available to other organisms in an edible form
- all non-photosynthetic organisms consumer (directly or indirectly) the energy rich organiz molecuel sproduced by photosynthetic organisms
Trophic levels
- primary producers: plants that conduct photosynthesis to obtain energy from sunlight
- primary consumers: herbivores that dine on primary producers
- secondary consumers: organisms that eat herbivores
- tertiary consumers: organisms that eat secondary consumers
- detrivores/decomposers: consumer waste rproducts and dead bodies
- omnivores: feed on multiple trophic levels
food chain
- linear sequence of who eats whom in a community
- in reality most species are eaten by more than one organism
food web
- represent how the trophic relationships of different organisms are interwoven
Gross primary productivity (GPP)
- rate at which the primary producers in a community turn solar energy into stored chemical energy via photosynthesis
- primary producers use some of this energy themselves for cellular respiration and other metabolic processes
net primary productivity (NPP)
- rate at which energy is incorporated into biomass that is actually available for consumption
- equals GPP minus energy lost through metabolism (cell resp)
- NPPP reflects the amount of energy available to consumers (in form of biomass)
Energy loss
Why?
How much?
Energy is lost as it is transferred from one trophic level to the next
On average, only about 10% of energy from one level is transferred to the next - 3 reasons:
- heat loss: energy used for respiration and other metabolic processes is dissipated as heat and lost to the community
- biomass availability: Not all biomass will be eaten. Defenses prevent consumption, grazers miss blades of grass, prey escapes
- Indigestibility: Not all biomass can be assimilated by consumers. Ex: tree bark cannot be digested for nutrients
Ecological efficiency
Ecological efficiency: transfer of energy from one trophic level to the next. 10% rule
Pyramid diagrams: illustrate the proportion of energy trasnferred from each trophic level
Loss of energy at each level puts a limit on the number of trophic levels in a community
higher trophic levels
- Less energy at higher levels
- fewer individuals and less biomass
- also lower species diversity
Direct predator and prey relationship
- predator and prey populations are constantly regulating each other
- as the number of prey increases, the number of predators also increases since there is an available food supply
- the number of prey then decreases because they are eaten by the greater number of predators
- followed by a decrease in the number of predators since there is now less food available
- changing carrying capacity
Ex: Snowshoe hare and Canada lynx
- hares are the lynx’s primary food source and limiting factor for population growth
- without the lynx, hare population would explode, causing an imbalance int he ecosystem
- without enough hares, the lynx would not survive
trophic cascades
One species can affect many others in a community
Trophic cascades: A species, usually a predator, in a food web can cause progression of effects across trophic levels based on their consumption
Keystone species:
- species that exerts an influence on a community disproportionate to its abundance
- changing the abundance of this species will induce a large trophic cascade in the community
keystone species
x
Indirect effects of trophic cascades
- interactions of a single consumer cancause a progression of indirect effects across successive trophic levels
- presence of absence of a single predator can influence not only the populations of its prey but also the structure of vegetation and populations of other species
Ex: wolves in yellowstone
- hunting had eliminated wolves by 1926
- elk population exploded
- browsed aspen trees so intensely that no new young grew
- browsed willows along streams which beavers needed
- 1995 wolves reintroduced
- elk avoided aspen groves
- aspen and willows regrew
- beaver colonies increased
Otter example
- in 1900s sea otters hunted until extinct
- feed on sea urchins
- sea urchins feed on kelp
- kelp provides food and habitat for other species
- when otter pop decreased, sea urchins increased and kelp forests declined
Keystone species- disproportionate influence, species richness
- can be disproportionate source of influence
- a source of food for many animals
Ex ochre sea star:
- rocky coast of pacific NA
- prefer mussels
- in absence of sea stars, mussels grow
- whens ea stars consume mussles, create bare space on rocks
- 18 species of animals and algae disappeared and only mussels remained
