Populations Flashcards
Population size =
No. individuals in selected quadrats /no. selected quadrats
X total no. quadrats
Population density
Population size/ area
X total no. quadrats
= no of individuals per m ^2
The number of that species per unit area
Proportion of marked organisms in the population is equal to the proportion of marked organisms in the sample
M/N = m/n
Population size estimated
N = Mn/m
N is
The population size to be estimated
M is
The number of members of the population that are captured initially and marked
n is
The number of members of the population that are present in the second capture
m is
The number of members of this second capture that are marked
Quadrats
Square or circular frame to mark out an area to be sampled
Transects
Is a line marked through an area of study (a rope or a piece of string)
Chose a line that has the most plants/immobile animal groups
Use them when the studied area is too big for quadrats
May not give an accurate representation of the diversity and populations of species
Capture-recapture
Technique for estimating a population size of mobile species
Relies on the captured sample redistributing equally throughout the population and being recaptured at the same frequency as individuals that have not been captured
Carrying capacity
The maximum population size of the species that the environment can sustain
Determined by the amount of available resources (food, water, habitat)
Density dependence
As the density of individuals in a population increases, these individuals within the same species begin competing with each others or with other species for the available resources.
In which per capita population progressively fewer resources will be available to sustain it
Population dynamics
Refers to the ecological (biotic and abiotic) interactions that lead to fluctuations in population size. It includes how populations of a species change in size and structure over time
The abundance
Of a species is a specific measure of a populations size or density in an ecosystem. It’s not just a measure of the number of individuals; it includes specifically where in the habitat they live, breed or hunt
r - selected
- Pattern of rapid increase, were the maximum reproductive potential of the species is reached, then the population declines (or crashes) in numbers
- To survive they must colonise new environments quickly
- The species in this group are characterised by being of smaller size, having short life cycles and, in animals, a lack of parental care for young
- They grow and reproduce quickly
r - selected examples
Mice
Toads
Weeds
Oysters
Locusts
K - selected
Live longer, longer breeding cycles, bred later in life, have fewer offspring and devote time and effort to ensuring the survival of the offspring to reproductive maturity
They are typically strong competitors in a crowded niches that invest more heavily in fewer offspring, each of high has a relatively high probability of surviving to adulthood
K - selected examples
The female red kangaroo is able to manage the number of young that are born at any time
Humans
Elephants
Gorillas
Population composition
The characteristics of a population, such as age, sex ratios, age structure, population infertility rate and average number of offspring per female
Population growth rate (r)
(Birth rate + immigration rate) - (death rate + emigration rate)
(b+i) - (d+e)
Measuring distribution (3 types)
random distribution - irregularly spaced
Uniform (continuous) distribution - evenly spaced
Clumped (grouped) distribution - grouped together
Population growth curves
When a few members of a species colonise new and favourable habitat, their population increases rapidly
Density-dependent factors
Are biotic and include, predation, interspecific and intraspecific competiton, and the spread of disease
These only come into play when the population reaches a certain level, the larger the population, the stronger the impact
Density-independent factors
Affects all individuals in a population, severe weather conditions, volcanic activity or habitat destruction by clearing or fire
The chance of individuals surviving the impact of density-independent factors is the same independent of the population entity or size
Ecological niches
The way in which species function within their environment - the time they feed, what they feed on, where they live and when they reproduce
The concept of a niche includes the food sources and feeding activities of a species, its spatial habitat, its reproductive site and activities, its relationships and interactions with other species, and any abiotic factors that help the species perisit
Fundamental niche
Is the ideal niche a species would occupy if there were no competitors, predators or parasites
The realised niche (actually niche)
Is narrower
It results from an organism’s inability to exploit the resources of its habitat because of restrictions asked by other organisms
It is the actual space occupied by a species/organism
Resource partitioning
The division in the use of sources is called resource partitioning
Different species within an ecosystem generally don’t feed on the same food sources at the same time. They usually differ in the food source they prefer, their use of space and even the timing of activities
Competitive exclusion principle
The competition exclusion principle postulated that no two species can occur the same niche in the same environment for an extended period of time. Two similar species that compete for a resource cannot coexist in the same community
A keynote species
Is not necessarily abundant in number in a food web
The niche of a keystone species includes highly influential relationships with a number of other species in a food web.
A keystone species can have a large effect on population numbers of other species in a community even though it may not be abundant. It can prevent organisms from lower tropic levels form monopolising food resources and space
