Lecture 17 and 18- population ecology Flashcards
Define population.
All the individuals of a species in a given area.
What does population structure describe?
The age distribution of individuals in a population and how they are spread over the environment
Why is population structure studied?
Spatial distribution influences population stability
What is the number of individuals of a population per unit area called?
Population density
What changes the structure of a population?
Demographic events
What are some demographic events?
Birth, death, immigration, emigration
What is the study of population dynamics called?
Demography
What do most field studies of animals require?
Tagging or marking the animal
How are birds typically tagged?
Colored bands on the leg
How are butterflies typically tagged?
Placing colored spots on their wing
How are bees marked?
By placing numbered tags on their bodies
How are mammals marked?
Tags or dyeing their fur
How is information about an animals physiology, feeding behavior and socialization recorded?
Microchips and other types of electronic tagging
How else can the movement of individuals across long distances be tracked?
molecular markers
The chemical composition of feathers of what bird can be tracked as they migrate south?
American redstart
What does the chemical composition of american redstart feathers tell scientists?
Where they molted
Strong latitudinal gradient of hydrogen isotopes in precipitation
How are population densities estimated?
Counting the number of individuals in a representative habitat and extrapolating the counts to the entire ecosystem
Why is it harder to count mobile organisms?
They move into and out of the census area- instead they are captured, marked and then released
What equation is used to calculate the number of organisms after capture, mark, release?
m2/n2=n1/N m2= no.marked in 2nd sample n2=total number of individuals in 2nd sample n1= no.marked in 1st sample N= estimated population size
What do ecologists use estimates of population densities to estimtate?
The rate at which births, deaths and movements take place, how these rates are influenced by the environment, life histories and pop.densities.
How can information about birth and death rates in a population be displayed?
In a life table
What is the group of individuals born at the same time called?
A cohort
What is a life table constructed with?
Cohort, survivorship (the numbers still alive)
What else do life tables sometimes contain?
offspring produced by cohort- fecundity
What can life tables be used for?
To predict future trends in populations
What life table is used in the book?
1978 cohort of the Cactus Finch on isla daphne (galapagos archipelago)
How many cactus finch were in the cohort?
`210
How many of the cohort were alive in 1991 when the cohort stopped being followed?
3
What were the general patterns in the cactus finch cohort?
High mortality in 1st year
Dropped dramatically for several years
General increase in later years
Why was there year to year fluctuations in the cactus finch mortality rates?
Survival depends on seed production, correlated with rainfall
What survivorship curve is characteristic of songbirds?
The probability of surviving year to year is about the same over most of the life span after a few months, (straight line down)
What is the survivorship curve for offspring that produce many offspring which recieve little investment or prenatal care?
Survivorship is low among juveniles and high for the middle part of the life span
Give an example of an organism that produces many offspring with little investment.
Spergula vernalis- annual plant that grows on sand dunes in poland
Between what years did the united states experience the post world war II baby boom?
1947 and 1964
What was the average family size growth during the US’s post WWII baby boom?
from 2.5 to 3.8 children (4.3million babies in 1957)
What happened when baby boomers became parents in the 1980’s?
Produced another bulge in age distribution- baby-boom echo
What is a life history?
Describes how an organism allocates its time and energy among various activities
What is the latin name of the black rockfish?
Sebastes melanops
Where does Sebastes melanops live?
Off the pacific coast of North America
What does Sebastes malanops offer an example of
How life history traits influence growth of population that humans would like to manage
Why are female black rockfish more productive when they are older?
Larger- more eggs is proportional to size
More oil droplets in egg to give energy to hatchling
What happened when there was intensive black rockfish fishing off the coast of Oregon in 1996-1999?
Reduced average age from 9.5 to 6.5- less eggs produced, growth rate of larvae reduced 50%
What is the latin name for guppies?
Poecilia reticulata
Where do guppies live?
Trinidad
What was the guppies experiment for?
To test the influence of predation on the evolution of life history traits
How are predators and guppies distributed?
Guppies below the water fall are preyed on by large fish,
Guppies upstream of waterfall that cannot be sumounted by predators have low mortality rate
What is the difference between the guppies groups when in a lab?
Guppies in high predation site matured earlier, reproduced more frequently and produced more offspring per brood
What was the conclusion of the guppy study?
Predation favored early and frequent reproduction leading to change in guppy genotype
What do all populations have potential for?
Exponential growth
How can exponential growth be expressed?
net reproductive rate= change in no.individuals/change in time
=births-deaths *number of individuals
What is the highest value of r?(net reproductive rate)
r max
Intrinsic rate of increase (characteristic for each species)
Give an example of a species growing at rates close to its intrinsic rate of increase.
Northern elephant seals
Why can populations not maintain exponential growth for very long?
Environmental limits cause births to drop and deaths to rise
What name is given to the number of individuals an environment can support at one time?
Environmental carrying capacity (K)
What determines environmental carrying capacity?
Availability of resources:
- food
- nest sites
- shelter
- disease, predators, social interactions
What happens to population growth as density approaches carrying capacity?
Growth typically slows
What name is given to the typical graph of population size over time as density nears carrying capacity?
Logistic growth
What does population density influence?
Birth and death rate
What name is given to the way birth and death rates change with changes in population density?
Density dependent
Why are birth and death rates density dependent?
- Food becomes depleted- poorer nutrition
- Predators are attracted to high density
- Disease spreads more easily
What are some density independent factors?
Weather, natural events (hurricanes etc.)
In what animals was population density studied?
Song sparrows
What is the latin name for song sparrows?
Melospiza melodia
Where are song sparrows found?
Mandarte Island (off british columbia, canada)
What density independent factors effected the song sparrows?
Cold, snowy winters
What density dependent factors effected the song sparrows?
- No. breeding males limited by territorial behavior
- More breeding females, fewer offspring each one fledged
- More birds alive in winter, less chance juveniles would survive winter
What species are generally more stable?
Species with long lived individuals with low reproductive rates
What species are more vulnerable to environmental changes?
Small, short-lived individuals
What are most fluctuations in population density driven by?
Changes in biotic and abiotic environment that change environmental carrying capacity
What are two examples that change carrying capacity?
Episodic reproduction that generates population fluctuations
Resource fluctuations that generate consumer fluctuations
Give an fish example of episodic reproduction that generates population fluctuations
Lake Erie- 1944
Whitefish reproduction went well, dominates catches for several years
Give an plant example of episodic reproduction that generates population fluctuations
Most black cherry trees- wisconsin 1971 were established between 1931 and 1941
What do birds and mammals in boreal forests feed on? How do these trees reproduce?
seeds in conifer cones- most trees reproduce synchronously and episodically
Give an example of resource fluctuations generating consumer fluctuations.
Crossbills wander looking for where cones are produced
Jays and nutcrackers and squirrels store seeds during high production but there are still high mortality rates when few seeds are produced.
What factors enable some species to become more common than others?
- Use of abundant resources
- Small body sizes
- Newly introduced species
- complex social organization
What are the implications of the fact that species that use abundant resources generally reach higher population density?
Animals that eat plants typically reach higher population densities
What are the implications of the fact that species with small body sizes generally reach higher population density?
Population density decreases as body size increases because small individuals require less energy to survive
Why do some newly introduced species reach high population densities?
Escaped control of factors that prevented them becoming more abundant, temporarily achieve high population density
Give an example of a species introduced to a new region and was able to reach a much higher population density.
Zebra mussel Dreissena polymorpha
How did zebra mussel reach great lakes from europe in 1985?
Larvae carried in ballast water of commercial cargo ships
Give an example of unexplained differences in species abundance.
Douglas firs and giant sequoias- same source of energy and same nutrients
Desert pupfish in a single spring in death valley, smallmouth bass live in most rivers and lakes in eastern north america.
Why do species that arise by polyploidy have small ranges?
They start in a small, local population
Species that arise through a vicariant event typically have a _____ population size.
Large
Population divided into subpopulations live in …?
Habitat patches
What is the larger population to which subpopulations belong to called?
Metapopulation
What is the birth and death of a subpopulation?
Colonization of that habitat patch
Extinction in that patch
What is the name given when individuals moving between subpopulations prevent the extinction of declining subpopulations?
Rescue effect
Why are subpopulations more likely to become extinct then the entire population?
More likely to be effected by local disturbance and random fluctuations
What species gives a good illustration of the dynamics of metapopulations?
Checkerspot butterfly
What is the latin name of the checkerspot butterfly?
Euphydryas editha bayensis
What do checkerspot butterfly larvae feed on?
A few species of annual plants restricted to serpentine rock on hills south of San francisco
What happens to the plants checkerspot larvae feed on during drought?
Plants die early in spring, before caterpillars are old enough
What area recolonized other patches when they became extinct during drought?
Morgan Hill
How can the hypothesis that even small barriers to recolonization may reduce the number of species in a habitat patch be tested?
Trim moss growing on rocks to form distinct habitat patches- the number of small organisms (mostly arthropods springtails and mites) was observed over time
What were the results of the moss patches test?
40% species became extinct after 1 year
What was the result of the moss patches with some corridors?
14% species on patches connected by corridor extinct after 6 months
41% species on patches connected by psuedocorridors with gaps extinct after 6 months
What effects migratory birds?
Events on both breeding and wintering grounds, as well as places to stop and feed during migration
In a census of breeding birds conducted in Eastern wood, england, what happened between 1950 and 1980?
Wood pigeons doubled
Garden Warblers decreased to 0 in 1971
Blue tits increased
Why did pigeon population increase in the Easter Wood study?
Widespread adoption of oilseed rape as an agricultural crop
Why did Gardern Warbler population decrease?
Overwinter survival was poor due to drought in wintering grounds in West Africa
Why did blue tit population change?
Tree cutting in Eastern Wood stopped, more holes in which to nest became available.
When are births and growth rates of individuals at the highest?
When a population is well below carrying capacity
What can be high in fast reproducing populations?
Harvest rate
Growth rates of individuals is density dependent, so it is best to harvest….
Pre-reproductive individuals to allow others to grow faster
Why can some fish populations be harvested on a sustained basis?
Because few females can produce enough eggs to maintain the population
Where did overharvesting of fish occur in the 20th century?
Georges Bank off the coast of New England
What was Georges Bank a source of?
Cod, haddock, other prime food fish
What happened at Georges bank?
Exploited so heavily that commercial fishery could not be supported. Haddock rebounded to support fishery today by stopping commercial fishing until recovery
What happened to cod at Georges bank?
Managers reduced fishing pressure on cod slowly, cod population failed to increase.
What other industry has engaged in overharvesting?
Whaling (blue whales)
Why is management of whale populations difficult?
Whales reproduce at low rates over a long period of time, whales are distributed widely through the ocean, so are international and depend on cooperation
What was established as an international body to guide recovery of whale populations?
International whaling commission
Why can populations below carrying capacity withstand high death rates?
They have high birth rates
When is killing part of a population to reduce it density not effective?
When population dynamics are primarily influenced by density-dependent factors.
What is a more effective approach to reduce the numbers of a population that depends on density-dependent factors?
Remove its resources to lower carrying capacity
Give an example of humans controlling populations by introducing predatory species.
Opuntia and cactoblastis in Australia
Give an example of humans making things worse by introducing predatory species.
Cactoblastis in Mexico and southwestern US
Bufo marinus toad in Australia from central america.
What was Bufo marinus introduced to control in australia?
Cane beetle
What did the bufo marinus toad do?
Kills snakes and mammals that eat them
Outcompete native amphibians
What is Earth’s carrying capacity for humans set by?
The biospheres ability to absorb by-products of fossil fuel energy
