Population Dynamics Flashcards
5000 bce
A modern form of agriculture emerged
(years ago) on the x-axis and world population size on the y-axis
Global Footprint Network
On August 8th, 2016, the Global Footprint Network reported that the human population on earth had already consumed its yearly production.
e were borrowing three months of global production from the next year, 2017.
Carrying capacity
population size for a given species that a specific environment can sustain indefinitely, given the food, habitat, water, and other necessary resources available.
“A finite world can support only a finite population; therefore, population growth must eventually equal zero.” (Garrett Hardin, “The Tragedy of the Commons,” 1968)
Thomas Robert Malthus,
he power of population is indefinitely greater than the power in the earth to produce subsistence for man.”
regulations on human population growth are either
voluntary (for example, birth control, abstinence, or delayed marriage)
involuntary (for example, famine, disease, or war).
ecological footprint
measure of a person’s daily demands on the earth’s ecosystems.
It is the amount of biologically productive area of the earth (land and sea) needed to produce the resources a person consumes, in addition to the area needed to absorb and treat the resulting waste. It is measured in global hectares (gha).
global hectare represent
A global hectare represents the biological productivity found on one “average” hectare (a measure of area)
Populations change when
grow when birth rates exceed mortality rates. (birth rate > mortality rate)
shrink when mortality rates exceed birth rates. (birth rate < mortality rate)
remain stable when the two rates are similar. (birth rate = mortality rate)
movement through these stages is known as demographic transition.
Demographic transition model stages
stage 1
Birth and mortality rates are similar, so the population size remains stable.
Demographic transition model stages
stage 2
Mortality rates start to decline, but the birth rates stay relatively high. This causes the population size to start growing exponentially.
Demographic transition model stages
stage 3
Birth rates are starting to fall and the decline in the mortality rates has levelled off. Birth rates are still higher than mortality rates, so the population is still increasing, but it is starting to slow down.
Demographic transition model stages
stage 4
Birth and mortality rates are now similar again, so the population stops growing and eventually becomes stable.
Demographic transition model stages
stage 5
If the birth rate continues to decline and falls below the mortality rate, then the population will enter stage 5.
Here, the population size starts to decrease because there are more deaths than births.
Industrial Revolution 1700s
New machines and factories could make goods faster and more cheaply than ever before.
People migrated from farms into the growing cities to find work.
The Industrial Revolution brought a higher standard of living and lower mortality rates for many people.
Modern farm machinery and fertilization meant that more food could be harvested from the same amount of land, employing fewer people.
advances in sanitation, public health, and medicine led to a dramatic reduction in the mortality rate
As the Industrial Revolution progressed, the new lower mortality rates combined with traditionally high birth rates created a period of exponential growth
Green Revolution.
Norman Borlaug helped improve agricultural productivity.
Food production increased around the world, so most people in developing countries no longer experienced regular periods of starvation. Mortality rates dropped, but just like in developed countries, birth rates remained high. This led to a period of exponential population growth.
Future population trends
Slower growth stage 4 early stage 5
social and economic development
a lower risk of infant mortality
continuing urbanization
Environmental consequences of human population growth
Pollution climate change over consumption (tragedy of the commons Garrett Hardin) and habitat loss
Canadian social and economic aid
Formerly, it was done through the Canadian International Development Agency (CIDA)
population
group of individual organisms of the same species that live together in the same geographic area.
always changing due to
new individuals are added through births (natality)
immigration (individuals moving into a population)
loss through death (mortality)
emigration (individuals moving out of a population).
Population density (crude density)
how many individuals there are in a given area.
Population dispersion
how the individuals are distributed over the area.
ecological space (
size of the area that is actually usable by a species
o get a better estimate of how dense a population really is, biologists use ecological density (DE), which adjusts the area used in the calculation to reflect the amount of suitable habitat (SE) available for the species.
Clumped dispersion
Clumped dispersion occurs when organisms group together in an area.
In animals clumped dispersion, may occur for:
protection
exploitation of a resource
Uniform dispersion
that there is an equal spacing of individuals across an area
In animals, uniform dispersion can occur when each individual is guarding a similar-sized territory for feeding or nesting.
Random dispersion
individuals are scattered randomly over an area.
Quadrat sampling
used for counting abundant organisms, like plants, or organisms living beneath the soil, like earthworms, that do not move much and can easily be seen. one big square into smaller squares using a small square called a a quadrat
type I survivorship
elatively few offspring, but each one has a high probability of living to the maximum age. Mortality rates are low and constant for most of their life, but then increase rapidly as they approach the maximum age. The parents generally invest a lot of energy in feeding, caring for, and teaching their offspring, who have a better chance of survival, as a result. Species showing type 1 survivorship curves include birds, humans, and other mammals.
Type 2
pecies have a constant mortality rate throughout their life, so young and old have an equal chance of surviving
straight line down on angle
Type 3
high mortality rate when they are young, but this declines as they grow older. Many species of fish and plants, as well as sea turtles, show this type of survivorship curve.
other way J
fecundity.
number of offspring an individual can produce over its lifetime
(abiotic
physical
biotic
biological
Closed Population
Not changed by immigration or emigration
Separated from other populations by long distances or are surrounded by physical barriers that prevent them from moving in and out of the population.
An island in the middle of the ocean is generally closed to immigrants that can’t swim or fly
Open Population
Can be changed by immigration and emigration
No barrier preventing them from moving in and out of the population.
A population of moose in a patch of boreal forest in northern Ontario is considered to be an open population, because the moose can move in and out of it easily.
net population
change in population size after the combined effects of births, deaths, immigration, and emigration are accounted for.
Net population change = (b + i) – (d + e)
The four factors that affect population dynamic
births deaths immigration emigration Population dynamics are the result of an interaction between:
internal factors (for example, reproductive ability) external factors (for example, weather, food supply, predation, and disease)
Geometric growth
It happens in populations where individuals can only breed once per time period (like deer, which breed once per year).
On Day 0, the population size is 1. On the next day, it doubles to 2 and the day after that, it becomes 4, and so on.
graph like a J
exponential population growth
humans, can reproduce at any time of the year. This means that the population can grow continuously, since it is not restricted to fixed time periods
Biotic potential
maximum population growth rate that could occur under ideal conditions for an organism.
logistic growth
closely resembles what happens in natural populations The Lag phase The Log phase The Stationary phase s curve or sigmod curve
N is the population size at time t
r is the growth rate per individual
K is the carrying capacity
Phase of logistic population: First part of the curve lag
Population is slowly building up
Increase in population size is slow, because the population is still small.
Phase of logistic population: 2nd part of the curve log
Population increases geometrically or exponentially
Since there are enough resources to meet the needs of the population, population growth rate reaches its maximum and biotic potential.
As the population increases, it begins to run out of resources such as food, water, and space. Numbers increase until there are no longer enough available resources to maintain the high rate of population increase. At this point, the population growth rate begins to slow down and eventually stops when the population size reaches its carrying capacity (K).
Phase of logistic population: last part of curve - stationary
Population approaches its carrying capacity because
number of births = number of deaths
Eventually a dynamic equilibrium around its carrying capacity is maintained as
population growth rate = 0
density-dependent factors
internal factors
For animals, these factors can include:
the amount of food breeding territory available social dynamics predator avoidance opportunities the risk of parasites and disease, and so on.
For plants, the availability of resources like sunlight, water, and soil will depend on how many other plants are competing for them in the same area.
Density-independent factors
abiotic factors such as:
Extreme weather events Fires Droughts Volcanic eruptions Pollution
Levels of organization in ecological systems
Individuals form the lowest level of the hierarchy.
Populations are formed at the next level when individuals of the same species combine.
Communities form when populations of different species interact.
Ecosystems are formed when communities interact with each other, and with other biotic and abiotic processes.
niche
How an organism uses its habitat, and the way it utilizes the resources within it
Competition
two or more organisms are using the same set of resources in the same area to the disadvantage of each.
the interaction results in a negative outcome for each organism.
Competition can defined as:
Interspecific: between members of different species.
Intraspecific: among members of the same species
interference competition
two animals fighting over a resource
explotive competition
one animal eats all the fruit off the tree before the others can get to it
resource partitioning
Similar species that share the same area usually divide up the resources
morphological defence
involving the shape or structure of an organism.
thorns, spines, and stinging spikes
Chemical defence
Animals and plants have evolved chemicals that they can use to reduce predation.
For example, skunks can spray a noxious-smelling chemical
Cryptic colouration (or camouflage)
to hide themselves from predators.
Aposematic colouration:
warn predators that they are not good to eat. Instead of trying to hide from predators, these species have evolved dramatic colour displays to warn predators
Symbiosis
two species may live closely together and interact in ways that benefit at least one of the species.
Mutualism occurs when both participating species benefit from living closely together
commensalism-one species benefits while the other species does not (but is also not harmed)
Parasitism - micro or macro parasites
social parasitism
This does not involve a parasite consuming resources from its host’s body. Instead, the parasite manipulates the social behaviour of the host.
brood parasitism
A dramatic example of social parasitism is when a bird’s nest is taken over by another bird that uses the nest for its own eggs.
producers
Green plants like algae, pond lilies, and reeds
main primary consumers.
fish, insect larvae, and crayfish,
Secondary consumers,
leopard frogs, carnivorous fish (for example, bass), and insects (for example, water beetles) eat the herbivores
tertiary consumers,
predatory birds (for example, the blue heron) eat the primary consumers (for example, crayfish), as well as the secondary consumers (for example, leopard frogs and bass).
