population ecology (PP22) Flashcards
what are the levels of ecology
Organismal
How individual physiology & behaviour meet challenges
Population
Factors affecting population size & distribution
Community
Interactions between species
Ecosystem
Energy flow & chemical cycling between organisms & their environment
Global
Regional exchange of energy & materials, distribution of organisms around the planet
what is ecology
Field of science that studies interactions between organisms & their environment
what are biotic factors
Biotic interactions Between organisms (competition, predation, parasitism, mutualism)
what are abiotic factors
Temperature Water Sunlight Wind Rocks & soil (e.g. pH) Disturbances (e.g. fire, volcanic eruptions, hurricanes, etc.)
what is population ecology
Study of populations in relation to environment
Population ecology looks at the environmental influences on…
Population density & distribution
Age structure
Variations in population size
what is the difference between intraspecific and interspecific
intra: within species
inter: between species
explain population
- Group of individuals of the same species within a defined geographic region
- Rely on the same resources
- Influenced by similar environmental factors
- Likely to interact & breed with one-another
explain metapopulation
- Group of spatially separated populations of the same species which interact at some level
- GENE FLOW
- Fragmented subpopulations occupying spatially separate habitat patches in a fragmented landscape of unsuitable habitat
difference between immigration and emigration
Immigration: when organisms arrive at a new location & establish themselves at this location ‘permanently’ (inward bound)
Emigration: when organisms leave their original location (outward bound)
empty patches of land are susceptible to ?
colonization
what does persistence of local population depend on
Persistence of some local populations (sinks) depends on migration from nearby populations (sources)
what were the 4 conditions proposed before assuming that metapopulation dynamics explain species persistence:
- Patches should be discrete habitat areas of equal quality i.e. homogeneous
- No single population is large enough to ensure long-term survival
- Patches must be isolated but not to the extent of preventing re-colonization from adjacent patches
- Local population dynamics must be sufficiently asynchronous that simultaneous extinction of all local populations is unlikely
is each subpopulation stable or unstable
unstable (subject to random extinction / recolonization)
what does Dispersal among patches assure
long term viability
if an individual subpopulation goes extinct, can the overall population still persist?
yes
Some subpopulations do well while others do poorly
What are the 3 factors that must be taken into account when looking at populations
Size: number of individuals in the whole population
Density: number of individuals per unit area / volume
Dispersion: pattern of spacing among individuals within the boundaries of the population
what is the study of demography
Demography = study of the vital statistics of a population and how they change over time
What is population density and size the result of?
Result of a dynamic interplay between processes that add individuals to a population & those that remove them
what is the formula for population size?
Population size =
(Births + Immigration) – (Deaths + Emigration)
what is population regulation
tendency for population to be maintained around a characteristic abundance via action of density-dependent factors (both abiotic & biotic)
what is density affected by>
Density is affected by both intrinsic & extrinsic factors
explain intrinsic factors
Intrinsic:
Internal to the population
e.g. size & rate of growth of the population itself
explain extrinsic factors
Extrinsic:
Interactions with other parts of the community (forces external the population)
e.g. predation, parasitism, disease, stress / competition
what are the.3 types of population dispersion
Random
Clumped / clustered
Uniform
explain random dispersion and give an example
Position of each individual is independent of other individuals
Regions of high & low concentration / density
Suggests no external influences
e.g. Dandelions grow from windblown seeds that land at random & later germinate
possible when resources are limited or predation on one species
explain clumped/clustered dispersion and give an example
Individuals aggregate in patches
May be influenced by behaviour
Distribution typically exists around central resources
Often clustering of populations around water
Wolves: living in groups increases hunting effectiveness, spreads work of protecting & caring for young, & helps exclude other individuals from their territory
explain uniform dispersion and give an example
Individuals are evenly distributed
May be influenced by social interactions such as territoriality, such as between predators
Can arise artificially, such as at tree plantations
Penguins nesting on small islands often exhibit uniform spacing, maintained by aggressive interactions between neighbours
the rate of population growth can be expressed mathematically as:
This relationship can be rearranged to the following:
Nt = N1(1+r)^t
explain the exponential population growth model
- Model describes population growth in an idealized, unlimited environment
- Ignores immigration & emigration
- Growth rate (per capita increase) equals birth rate minus death rate
Rate of reproduction is at its maximum (intrinsic rate of increase)
This relationship is expressed as:
r = (∆N/∆t) / N1
(As per previous slide)
explain the logistic population growth model
- Exponential growth cannot be sustained for long in any population
- Must include the concept of carrying capacity (K)
- Maximum population size the environment can support
Does not include predation!
Per capita rate of increase declines as carrying capacity is reached
By incorporating K into our growth equation, we get a modified form, where r is multiplied by [1-(N/K)]
do populations always stabilize around their k constants
no, it varies
Growth of laboratory populations of paramecia fits an S-shaped curve
Some populations fluctuate greatly around K
Some populations overshoot K before settling down to a relatively stable density
what are reproduction rates determined by?
Number of offspring (reproduction)
Reproductive period (reproductive lifespan)
Age at beginning of reproductive period
what may finite ressources lead to
may lead to trade-offs between survival & reproduction
what are the benefits and disadvantages to live birth of small youth
Parental care of smaller broods may facilitate survival of offspring as well as parents but fewer offspring & high parental investment
what are the 2 major life traits that could be selected based on environmental conditions
r-selection: density-independent selection
Selects for life history traits that maximize reproduction
K-selection: density-dependent selection
Selects for life history traits that are sensitive to population density
explain r strategists and give example
- Opportunistic populations
- Characterized by exponential growth & sudden crashes
- High intrinsic rate of growth (r)
- Reproduce early, have many offspring
- Small offspring, mature rapidly,
- Little parental care
- High pre-mating mortality
- Generations are relatively short, large brood size
e.g. dandelions, insects, small mammals
explain k strategists and give an example
- Equilibrial populations
- Populations with sigmoid growth curves limited by -carrying capacity (K)
- Include relatively slow-breeding organisms
- Tend to live in stable, predictable habitats.
- Reproduce late, have small broods
- Large offspring, mature slowly
- Intensive parental care
- Generations are relatively long
e.g. oaks, large mammals
what are survivorship curves?
Graphic method of representing the number in a cohort alive at each life stage
what are the 3 types of survivorship curves
Type I: Organisms that live out a full reproductive period. Common in large mammals. K-strategists.
Type II: Mortality rate constant. Just as likely to die at any time in the lifespan. Hydras, rodents, some birds. Mixed strategy.
Type III: High pre-reproductive mortality. Little or no parental care, metamorphosis in larval stage. Fish, most invertebrates. r-strategists.
what are the 2 types of populations
Density-independent populations (r-strategists)
Birth rate & death rate do not change with population density
Density-dependent populations (K-strategists)
Birth rates fall & death rates rise with population density
LOOK AT SLIDES FOR EQUILIBIRUM POPULATION GRAPHS
notes
What is an example of negative feedback that regulates population growth and what is it affected by
Density-dependent birth & death rates are an example of negative feedback that regulates population growth
Affected by many different mechanisms:
Competition for resources Territoriality Predation Health Intrinsic Factors
explain competition for ressources
In crowded populations, increasing population density intensifies intraspecific competition for resources
explain territoriality and give exmaple
Defense of a specific geographical area against others (intraspecific interaction)
May limit density
Cheetahs are highly territorial - use chemical communication to warn other cheetahs of their boundaries
Oceanic birds exhibit territoriality in nesting behavior
explain predation
As a prey population builds up (increases in density), predators may feed preferentially on that species
Convenience factor:
explain health and intrinsic factors
Population density can influence the health and survival of organisms
e.g. pathogens can spread more rapidly in dense populations
For some populations, intrinsic (physiological) factors appear to regulate population size
e.g. white-footed mice get stressed at high densities
what are the 3 ways a disease will respond to an increase in population density?
Density-dependent: spread proportionally with density
As density increases, the disease prevalence does as well
Density-independent: spread proportionally & plateau
Occurs when a disease reaches a point where the species’ behaviour prevents it from spreading further (e.g. STIs)
Vector-dependent: spread as density increases, but will then decline
Requires an intermediate species to transfer between prey, & will decline once there are insufficient vectors (e.g. malaria)
what is a cohort and what is it used for?
Cohort: group within a population, comprised of individuals born at roughly the same time
Eliminates age variable
used for tracking changes in population
what can we create after studying cohorts and whats it use
Create age-structure charts
Can give predictions about changes to the population
Older cohorts will not likely contribute to growth (no longer producing offspring)
Youngest cohorts will have a delay before they can contribute to population changes
what are the 4 types of situations on an age chart
Rapid growth: # born»_space;> # dying
Slow growth: # born > # dying
Zero growth: # born = # dying
Negative growth: # born < # dying
can a population grow indefinitely?
no
demographic transition model
look at slides for phases
what is a decrease in mortality influenced by
Influenced by:
Personal hygiene
Improved sanitation
Modern medicine
what is a decrease in mortality influenced by
Influenced by:
Empowerment of women
Rising standard of living
Education & access to contraceptives
what does the ecological footprint summarize?
Summarizes the aggregate land & water area needed to sustain the people of a nation
One measure of how close we are to the carrying capacity (K) of the planet
