Population growth Flashcards
What is a population?
All individuals of the same species living in the same habitat that can interbreed and produce fertile offspring.
What is population dispersion?
The spatial distribution of individuals within the geographical range
What is random dispersion?
Individuals are distributed unpredictably within a uniform habitat.
What is clumped dispersion?
Individuals group together due to patchy habitats, social groups, or reproductive patterns.
What is uniform dispersion?
Individuals repel each other and tend to be evenly spaced because resources are short in supply.
What is demography?
The statistical study of changes in population size,age-structure and sex ratios
It predicts the probability of a population to die.
Important for the management and conservation of species.
What is exponential growth?
The Per capita birth rate in the population during the specific period divided by the population size.
The per capita death rate is the amount of deaths divided by the population size during the same period.
Changes in population sizes.
The difference in births and deaths (b-d) is the per capita growth rate (r) of the population expressed per individual unit per time
Using per capita growth rate the exponential equation can be written - dN/dt = (b-d)N or dN/dt = rN
r>0 the population is growing
r<0 population is declining
r=0 population is stagnant
Do populations grow exponentially?
Exponential model:
When resources are unlimited
More births than deaths
even if r is constant the population will increase.
Logistical model:
Limited resources
As populations encroach on the carrying capacity of a resource the growth rate decreases.
What is carrying capacity?
the maximum number of individuals that a specific resource in a given area can maintain.
Varies from environment/habitat to another.
Limited to amount of available resources.
Can populations grow under ideal conditions?
Per capita birth rate is high
per capita death rate is low
per capita growth rate is as high as it can be.
Max per capita growth rate (rmax) is the populations intrinsic rate of increase
What is the Logistic model?
Per capita growth rate decreases as it reaches the carrying capacity.
Start with the exponential model and add a section that accounts for the decrease in per capita growth as it approached the carrying capacity.
Assumes the per capita growth rate decreases as the population increases.
S-shaped graph of population size over time.
Slow population growth when population is small.
BUt also grows slowly when population is large because low per capita growth rate
What is interspecific compitition?
Represented by the logistic model
dependance of 2 or more individuals of the same species on the same limiting resource.
Animals: food, water, nesting sites, space
Plants: sunlight, water, inorganic nutrients, growing space.
Exponential vs. Logistic growth
Density-dependant mortality: (logistic)
Limited space, food = more diseases and predators
Density independent effects: (exponential)
Catastrophes that kill at the same rate whether there is 1 or 1000 individuals.
Population cycles
Depends on combinations of density dependant and density independent factors.
Stable
Cyclic
Chaotic
Metapopulation dynamics
The study of networds of seperate populations that interact with each other through the exchange of individuals.
Suitable - births > death
Sub-optimal - births < deaths
Unsuitable - no population immediate death.
Ideally adapted organisms
Reproduces afer own birth
Produces large clutches of large offspring
reproduces repeatedly and often
Out-competes competitors
Lives forever
If fitness if key why does an organism not exist?
Life cycle is a series of trade-offs
A compromise allocation of the resources available to it
Trade-off btwn a long life and many births each year.
Birds that raise more offspring per year, have a higher probability of dying that year.
Number of breeding seasons
Iteroparous = servel offspring over the course of several breeding years.
Semelparous = focus all reproductive energy into every single breeding season. Long lived or short lived (agave).
Where do we find short maturity times?
ephemeral habitats
Species vary across a continum of habitats - intrinsic rate of natural increase is fast and density independent. or mortality is density dependant and equal to the carrying capacity.
r -selected species reproduction
Reproduce early in short lives
have many offspring once
No parental care or investment
K-selected species reproduction
Reproduce late in long life
few large offspring
Large parental care and investment
Human population growth
average annual growth = 1.2%
Growth rates per nation vary widely
Graphs:
Mean Annual Population Grow Rates
Age Distribution for Different Growth rates
The demographic Transition Model
What is a community?
All the species that occur together at any particular locality / that exist in a set environment
What predicts the type of species that can occur in a community?
Abiotic environment
What is an assamblage?
subset of species in a community
Predation
Predators gain nutrients and energy when prey is killed or injured.
Herbivory
Herbivores gain nutrients and energy when plants are eaten
Parasitism
Parasites gain nutrients and energy when they kill or injure hosts.
Competition
Both competing populations lose access to some resources.
Commensalism
One population benefits the other population is unaffected.
Mutualism
Both Populations benefit.
Importance of predators and herbivores?
Both have evolved specialized structures and behaviours to help them obtain food.
Some species only feed on one type of food - specialists
Other species eat a wide variety of food - generalists
Carnivore consume other animals
Herbivores consume plants
Interactions btwn ecological prcesses
Predation is density dependent and lowers competition.
Experiments show that removal of a predator leads to population explosion of the prey and local extinction of other species.
Plant defenses against herbivores
Spines, thorns, irritating hairs and poisonous chemicals
Other compounds mimic the structure of insect hormones, which deters insects from consuming them
Plants can also increase the production of toxic compounds in response to herbivore-feeding
Some herbivores have coevolved to recognize odors and avoid toxic plants or defenses against the plants.
Passive predation defences
Mimicry - look like something else that is unappatizing
Cryptic colouration - blend into surroundings
Startling displays - display that increase size or ferocity
Hide - mimic as bird poo
Active predation defences
Sharp barbs when threatend (porcupines)
FIght back by biting or charging (bulls)
Chemical defenses (skunks)
Protection with poison from plants
