Population Growth
Population dynamics
• Rate of increase: the speed of change in
population size which is affected by one or
more of these:
• Fecundity rate
• Mortality rate
• Age distribution
Rate of increase
• Determined by the rate of growth in animal
populations.
• It could positive when population increasing
and negative when decreasing
• Rate of increase is determined by 2 things
1. Environment effect (Amount of food available)
2. Intrinsic effect (The intrinsic ability of the sp. to
convert the extra energy into enhanced fecundity
and decrease mortality).
• Intrinsic rate of increase
Fecundity rate
• A population’s rate of increase is
determined by its size which in turn is
determined by birth rate.
• It can be measured by fecundity rate: Is
the number of female live births per female
per unit of time
Mortality rate
• Animals that die over a year is another
important determinant of rate of increase
• It is measured by mortality rate: No. of
animals die during a unit of time divided by
the number of alive at the beginning of the
time unit.
Dispersal, dispersion, and
Distribution
Dispersal
• The movement that an individual animal
makes from its place of birth to the place
where it reproduce.
• Two kinds of dispersal
1. Presaturation: Juveniles leave natal home even
when density is low
1. Voluntary innately by their genes
2. The adult forcibly exclude juveniles
2. Saturation: when population reaches a
threshold density determined by food limitation
Dispersal
• Patterns of dispersal is related to mating system
• Dispersal fall into three broad categories:
1. Competition for mates
2. Avoidance for inbreeding
3. Competition for resources
Male reproductive success is limited by number of mates
so cat. 1 is important
No evidence of inbreeding depression or avoidance in
social carnivores. In general inbreeding depression
depends on sp. (Ex. wolves)
In Polygynous sp. Female invest more in offspring than do
males so reproductive success is determined by cat. 3
Dispersal tend to have lower survival than those that
remain in natal area. Survival declines with the distance of
dispersal due to the increasing probability of predation:
Ex. Arctic ground squirrel due to dispersion survival rate
went from 73% to 25-40%.
the survival of dispersing ferrets in New Zealand was
100% when predators had been removed compared to
19-71% in the predator presence.
Dispersion
• Is the pattern of spatial distribution taken by
the animal of an area.
• Dispersion might be:
1. Random: the variance of distribution equal its mean
2. Clumped: the variance greater than the mean
3. Spaced: the variance less than the mean
• Dispersion is affected by home range of
individuals which in turn is affected by habitat
(habitat preference) and gender.
Distribution
• The distribution of a sp. is the area
occupied by that sp.
• Distribution is determined by temp.,
rainfall, day length, season, and biotic
factor.
Temperature
• Temp. can limit animal distribution through direct
effect on their physiology or indirectly by affecting
resources.
• The limiting effect of temp. changes the range of
several sp. during historic times. And today due to
global warming changes in distribution of wildlife
sp. Are expected.
– Ex. Cold is clearly an important factor limiting sp.
Distribution
– Movement of large animals can be affected by temp.
(WB)
– Adaptation of animals in cold weather to conserve energy
(Hibernation, lowering body temp. ex bears and humming
birds)
Water loss and heat stress
• High temp. combined with high solar
radiation and restricted water supply affect
animal distribution.
• In high-rain fall areas water supply
determines the distribution of animals
• In arid regions all the three have
interrelated effect on animals
• Various adaptation to overcome these
conditions
High temp avoided by
• Using shade in the middle of the day
• Solar radiation restricts the movement of large animals with
dark coats (elephants and buffalo)
• Restricting feeding to hours of darkness at driest times
animals switch from grazing to browsing
• High heat can be avoided by sweating for evaporative
cooling in large animals and panting in small animals
• Some sp. adapt to extreme arid condition by allowing their
body temp to rise before they start panting (gazelles)
• Adaptation for water conservation (camel, dikdik)
• Even in cold regions there is a restricted
availability of water for wildlife
Day length, Seasonality, and Biotic
factor
• Day length (photoperiod) affect the No. of hours
available for feeding and breeding season
• Distribution is limited by season length, number
of days available for breeding above a certain
temp.
• Abiotic factor interact with biotic process
predation and competition to limit sp. range
Distribution abundance and range
collapse
• Major pattern in ecology is the +ve
relationship between range of sp and its
abundance.
• What happens to sp. range when sp.
Decline?
– Analysis of a wide range contraction in a wide
variety of sp suggest that population collapse
first at the center leaving isolated fragments on
the periphery
Sp reintroduction or invasion
• Many sp have been eliminated from their traditional
range for different reasons (Bison) and then they
were re-established to parts of their former ranges.
Other sp benefit from the availability of resources in
certain areas, invade it, and establish new
populations
• Re-introduced sp have plenty of resources with
which to grow and multiply
Dispersal and sustainability of
Metapopulations
• Dispersal plays a key role in
understanding the dynamic of sp that are
subdivided for a reason or another into
discrete metapopulation.
• Human environmental impacts often lead
to fragmentation of natural areas creating
effective metapopulation from a
populations that were continuously
distributed in the near past.
Basic principles of metapopulation
dynamic
• Metapopulation dynamic of a single sp. (where extinction rate does not get
translated into dangerous collapse of a population because of a stream of colonist from the
remaining occupied sites)
• Habitat loss and metapopulation collapse
• Fragmented territorial systems
• Source-sink (fraction of patches sustain +ve subpopulation growth (source) whereas
individuals in other patches always experience higher rates of mortality than birth (sink),
with sources sites supplying steady stream of dispersers that fan out to surrounding sinks )
• mainland-island-systems (patches are large or productive enough to sustain
permanent population whereas others are small or unproductive enough that local
extinction is common with both sustaining a positive population growth)