Flashcards in Population Ecology Deck (128):
What is population ecology?
The scientific study of the distribution and abundance of organisms, the interactions that determine that distribution and abundance, and the relationships between organisms and the transformation and flux of energy and matter
What is a population?
The total number of individuals of one species in a defined area
What is a community?
All the populations of all species in a defined area
What do population ecologists seek to understand?
Variation in life histories
Evolutionary forces which produce patterns in communities
How populations interact with each other and the environment
Population growth, regulation and dynamics
What is the name for the study of population growth, regulation and dynamics?
What does population ecology explore?
How biotic and abiotic factors influence the density, distribution, size and age structure of populations
What is adaptation?
The evolutionary process whereby organisms become better suited to their environments
What are life histories?
The role of the changing environment on events affecting growth, survival, development and reproduction
What are the two types of cause that lead to a species occurring where they do?
What is the ultimate cause?
Through natural selection organisms become adapted to maximise their fitness in a particular environment
What are the three types of fitness?
What is direct fitness?
The number of offspring an individual produces relative to others in the population
What is indirect fitness?
Derived from shared genes with kin other than the individuals direct offspring such as cousins, nieces and nephews
What is inclusive fitness?
The sum of direct and indirect fitness gains
What is a proximate cause?
The current environmental factors (both biotic and abiotic) which determine where an organism can live
What are biotic factors?
What are the two types of biotic factors?
Intra-specific: competition (within species)
Inter-specific: competition, predation, parasites and disease (between species)
What are abiotic factors?
These factors are often entangled
What is a response curve?
Shows how the abiotic features of the environment affect how well an organism functions
What is an ecological niche?
The role and position a species has in its environment; how it meets its needs for food and shelter, how it survives and how it reproduces. Includes its interactions with all biotic and abiotic factors of its environment
What is the name for a niche in the absence of other organisms?
What is the name for a niche in which other organisms are present?
What is a habitat?
An objective description of an environment
What is the result of environmental variability?
Natural selection always has a ‘moving target’
What different characteristics can environmental variability have?
It can be temporal or spatial
It can be deterministic and predictable or stochastic and unpredictable
Features of deterministic environmental change
Gradual shift, long term changes
Distributions of species tend to shift
What is acclimation or acclimatisation?
The process by which and individual organism adapted to a gradual change in its environment. This happens in a short period within the organism’s lifetime.
It may occur discretely or in a periodic cycle e.g. moulting
What is phenotypic plasticity?
The ability of an organism to change its phenotype in response to changes in the environment.
Includes all types of environmentally induced changes, which may or may not be permanent.
More important for immobile that mobile organism
How do species move to avoid adverse condition?
Migration or dispersal
What is hibernation?
A state or arrested development which allows organisms to survive periods of adverse condition and synchronise their life cycle development within the environmental conditions
What is the life history theory?
The pattern and duration of key events in an organisms lifetime which affect the number of offspring produced - natural selection shapes their life history to produce the most offspring
What is an iteroparous organism?
An organism that can reproduce many times in its life
What is a semelparous organism?
An organism that only breeds once in its life
Some semelparous species are annual - they have a single generation in a year
What is the cost of reproduction?
Resources used for reproduction cannot be used for other important processes such as growth
What is the Latin name for the hard beech?
How is growth visible in hard beech trees?
Growth is visible as rings
The thickness of the ring represents the investment in growth
What was the name for good years when the hard beech trees produced heavy crops of seeds?
Who studied the trade-off between growth and reproduction in hard beech?
Monks and Kelly (2006)
What were the results about trade-off between growth and reproduction?
On years of high seedfall, the annual ring growth was depressed relative to the previous year
What is a K-selected life history?
Subsist near the carrying capacity of the environment (K)
Produce low number of offspring over longer span of time
High parental investment
Favours evolution of timed life history strategies such as seasonal or diurnal resting stage
Complex life cycles
Features of stochastic environmental change
Catastrophic events cause high levels of mortality
Ephemeral habitats - only available for short periods of time
What is an R-selected life history?
Have populations that fluctuate in response to unpredictable changes in the environment
High growth rate (r)
Tend to produce a high number of offspring with minimal parental care
What type of environment are K selected organisms best suited for?
What type of environment are r-selected organisms best suited to?
What is abundance in population ecology?
The number of individuals in a population
What is density in population ecology?
Number of individuals per unit area/volume
What is dispersion in population ecology?
Pattern of spacing between individuals within the population
Methods of measuring abundance?
Most sampling based on measures of RELATIVE abundance:
Number per sample
Catch per unit effort
Counts in quadrants
Counts on transacts
What are examples of indirect measures of abundance?
Faecal counts / scats
What are the 4 factors that must be considered when picking a sampling technique?
3. Cost effective
4. Biologically relevant
What types of markings are used in organisms during mark release recapture?
Hair tuft removal
Recognition of individual colour patterns
What is the equation used to calculate the total population size in mark release recapture?
Total population size =
(no. marked in sample 1 x total caught in 2nd sample ) / no. marked animals in 2nd sample
How does distribution affect the probability of detection?
The pattern of distribution is not permanent for each species - distribution patterns often change seasonally
What are the three observed types of population distribution?
Features of aggregated distributions
Most common type
Found in environments with patchy resources - animals clump around resources
Also clustered due to social factors such as family groups
Prey clumped in areas where they can hide from predators
Features of uniform distributions
Need to maximise space between individuals due to competition or direct social interactions
Plants can exhibit uniform distributions
What is an example of a plant which exhibits uniform distributions?
Creosote bushes in Southwest USA - releases terpenes to inhibit the growth of other plants around it
Features of random distributions
Rare because biotic and abiotic factors cause organisms to be either clustered or spread apart
Can occur in plants with wind-dispersed seeds and marine larval forms dispersed by sea currents that settle randomly
What does sample distribution affect?
How many samples we need to take to measure the abundance accurately
Our ability to compare populations
How we handle, analyse and interpret the data
What is the change in population size equivalent to?
Births + immigrants - deaths - emigrants
What is the k-value?
‘Killing power’ - uncovers which life phase has the highest mortality
What is R(0)?
Basic reproductive rate - mean number of offspring produced by an individual by the end of the cohort
What is r?
The intrinsic rate of natural increase - the per capita rate of increase
What is a cohort life table?
Dynamic, follows a cohort over time
What is a static life table?
Snapshot of the population at one time
What is age structure?
Relative number of individuals of each age in the population. They can be used to predict a population’s growth trend, and illuminate social conditions in humans
What is a survivorship curve?
y-axis: number of organisms surviving in logarithmic scale
x-axis: age, as a proportion of maximum life span
Informs us about causes of mortality
Reflects r/K strategies
What is the relationship between body size and abundance?
Bigger species are less abundant
What is the population growth rate when resources are unlimited?
Geometric or exponential
What is exponential growth?
Continuous, occurs if reproduction happens at any time
What is geometric growth?
Pulsed, occurs if reproduction is seasonal
What is the name for growth rate as it slows and stops and resources are depleted?
Logistic or sigmoidal growth
What is the name for the population size at which growth stops?
what is K?
The number of individuals that the environment can support - birth rate is equal to death rate and population growth is zero
What are the primary demographic factors affecting population abundance?
What are the secondary demographic factors affecting population abundance?
What are density-independent demographic factors?
Factors that act in a density-independent manner have an effect on births and deaths which is not related to the size of the population
What are examples of density-independent factors?
Pollutants in environment
Seasonal cycles such as monsoons
Catastrophic factors such as fires and hurricanes
Example of species affected by density-independent population growth
Thrips in Australia
Eat rose pollen, which is available all year
In winter, the cold temperatures lower the development and fecundity of thrips, so population decreases
In spring, rates increase and populations rise
Growth checked by summer heat before density-dependent factors important
Weather accounts for 78% of population size variance
Density-independent factors on amphibians
Pollutants cause environmental stress, limiting population growth
Pesticides and other toxins disrupt their endocrine system
Direct increases in mortality l, indirect limitation in growth, development and fecundity
Increases deformities, delays development so more vulnerable to predators
Limits population growth irrespective of population size
Factors that act in a density-dependent manner have an effect on births and deaths which is directly related to population size
What are 5 mechanisms of density-dependent regulation?
Competition for resources - high density means higher competition
Disease - increased density increases disease transmission rates
Predation - predator catches more prey as prey population increases
Territoriality - increased competition for space
Intrinsic factor - higher densities can result in aggressive interactions s and hormonal changes affecting reproductive rates
What correlation do density-dependent factors have to population size?
Positive or negative
What is the allee effect?
Negative density dependence
Population growth rate low at low density due to low chance of animals finding mates or plants being pollinated
As a result newly established populations grow very slowly
What are factors that determine a population’s abundance?
Determination of the precise abundance of individuals will reflect the combined affects of all the factors and all the processes that affect a population, whether they are dependent or independent of density
What are factors that regulate a population’s abundance?
Regulation is the tendency of a population to decrease in size when it is above a particular level, but to increase in size when below that level
What is the problem if births and deaths are density-independent?
There is no stability - there will either be a continuous growth or continuous decline to extinction
What type of factors regulate abundance?
What is monotonic damping?
When there is a low intensity of density dependence, abundance plateaus around carrying capacity
What can Harcourt’s life tables be used for?
To distinguish the importance of density dependent and density independent factors
What is an example of density dependent and independent factors interacting?
Weather effects on population are density independent, but the effects are more significant when a population is at K and resources per individual are in short supply
What is maximum sustainable yield?
The largest theoretical yield (sustainable harvest) over an indefinite period
MSY aims to maintain population size at point maximum growth by harvesting individuals that would normally be added to the population
What are the 5 problems with applying maximum sustainable yield?
1. Very difficult to get accurate estimates of population size
2. Carrying capacity changes; impossible to estimate
3. Basic demographic data rare; varies between populations
4. Difficult to get measured of other forms of mortality - what regulates the population naturally?
5. Social systems and mating strategies often unknown
Example of MSY applied wrongly
Has caused collapse of many fisheries worldwide
Ignores several key demographic factors - size and age of fish being taken and their reproductive status. Also ignores ecosystem damage by exploitation and bycatch
What are direct biological interactions?
Consumption of another individual, mutual benefit (mutualism e.g. symbiosis)
What are indirect biological interactions?
Common enemies - shared predator
What is mutualism?
Both species benefit from interaction
What is commensalism?
One species benefits, the other is unaffected
What is competition?
Each species affected negatively from interaction
What is antagonism?
One species benefits, one disadvantaged
What is amensalism?
One species affected nagatively, the other is unaffected
Examples of mutualism?
Birds removing parasites
Nitrogen fixation by fungi (lichen)
Photosynthesis by algae living within coral polyps
What does it mean when a species is obligate?
That species can not survive without interactions with another species in the long or short term
What is the problem with commensalism?
Close interaction of two organisms unlikely to be completely neutral
What is the definition of competition?
Competition is an interaction between individuals brought about by a shared requirement for a resource in limited supply and leading to a reduction in the survivorship, growth or reproduction in the individuals concerned
Example of commensalism?
Epiphytes may intercept nutrients that otherwise would go to host plant; may shade host tree
What are the two types of competition?
What are the features of competitive interactions?
1. Need spatial and temporal co-occurrence
2. Increase in intensity as the density, phylogenetic similarity and niche overlap of competing species increase
What is interference competition?
Between individuals if they interfere with other’s foraging/reproduction
What is exploitation competition?
Use of resources depletes the amount available to others
What is apparent competition?
Occurs indirectly between two species which are both preyed upon by the same predator
What is contest competition?
Usually the result of interference competition
One species ‘wins’ and monopolises all of the resource - other species population crashes
What is scramble competition?
Usually result of exploitation competition
Resource shared equally between both species, but due to resource being finite, both populations eventually crash
What outcome is usually seen in a stable environment?
K-selected organisms have a higher competitive ability as they are specialists
What outcome is usually seen in an unstable environment?
r-selected organisms have a lower competitive ability as they are generalists
What is resource petitioning?
Differentiation of niches leading to species coexistence
What is the competitive exclusion principle?
One much can only carry a single species, which is why competition leads to exclusion of all but one species
How is a fundamental niche found?
Remove all competing species, and see what niche the species occupies
What is a realised niche?
A niche occupied with competing species present - many be smaller than fundamental niche
What is bottom-up control?
Where resources are limited, populations decline as individuals compete for access to the limiting resources
What are examples of antagonism?
What form of antagonism is the largest factor in evolutionary time changing phenotypes?
What is top-down control?
Predation influencing the size of a prey population
Works together with bottom-up control
What is predator-mediated coexistence?
Predator feeds on competitively dominant prey species
By reducing its numbers the predator releases competitive inferior prey from suppression by dominant species
Predator therefore allows more species to coexist than possible in absence of predator
What can be the opposite problem of predation?
If a predator feeds preferentially on competitively inferior prey species, predation further reduces the number of species in the community
What are predator-prey cycles characterised by?
Regular increases and decreases in numbers of predator and prey
Lag between population responses
Extrinsic factors affecting cycles in population