Different Biotic Potential and Environmental Resistance

Different Biotic Potential and Environmental Resistance.
Objectives:
 At the end of the lesson, you should be able to describe how an

ecosystem’s biotic potential and environmental resistance can affect
population growth.
 Explain the limiting factors of biotic potential.
 Explain how limiting factors affect organisms and ecosystems, and
 Categorize the different biotic potential and environmental resistance.
Definitions:
Biotic Potential
-is the maximum capacity of an individual or population to reproduce under optimal

environmental conditions. Populations rarely reproduce at their biotic potential
because of limiting factors such as disease, predation, and restricted food resources.
Environmental Resistance
-is the sum of the environmental factors (such as drought, mineral deficiencies, and
competition) that tend to restrict the biotic potential of an organism or kind of
organism and impose a limit on numerical increase.
Biotic Potential
The biotic potential of an organism is the maximum number of offspring that a species
could produce if there were unlimited resources.
Different factors that regulate the biotic potential of organisms:

1. Birth Potential
2. Capacity for Survival
3. Breeding Frequency
4. Length of Reproductive Life
Birth Potential
This is the maximum number of offspring per birth.
(i.e. how many babies something has).
Ex. Whooping cranes lay 2 eggs per year but usually only 1 survives so the birth
potential would equal 1
The biotic potential among organisms varies from species to species. Similar to
humans, many large mammals produce one offspring per year or breeding season. On
the other hand, insects produce thousands of offspring per year. Therefore, large
organisms have relatively lower biotic potential than smaller organisms.
On the average, spiders are capable of producing hundreds of offspring at a time, cats
and dogs can produce four to eight offspring at a time, and humans can only produce
one to three offspring at a time. The different biotic potentials of organisms can be
attributed to several factors such as survival rate of their offspring, frequency of
reproduction, and reproductive lifespan.
Capacity for Survival
This is the number of offspring that reach reproductive age.
Ex. Turtles lay tons of eggs at a time but only a few make it to the ocean and then even
fewer actually live to reproductive age
Breeding Frequency
This is how often an organism reproduces in a year. Ex. Elk mate only once a year
while mice or rabbits mate multiple times in a year
Length of Reproductive Life This is how long in an animal’s life that it can produce
offspring. Ex. African elephants can reproduce until they are about 90 years old but
can’t start reproducing until they are 15. So they can reproduce for approximately 75
years.
These factors prevent organisms from reaching their biotic potential. Any resource that
is short in supply is a limiting factor (food, water, territory, pollutants, toxins, etc.)
Limiting Factors
There are abiotic and biotic factors that affect the growth of a population. Abiotic:
sunlight, temperature.
Carrying Capacity
This is the maximum number of individuals of a species that can be supported by an
ecosystem. This is determined by food and water availability, shelter, etc. Carrying
Capacity This system helps to ensure that one population isn’t taking over the
ecosystem. It helps to maintain equilibrium.
Density Dependent Factors
A factor that affects members of a population because of population density. Examples:
food supply, disease, exotic species, increased predation, competition Density
Independent Factors A factor that affects a population regardless of population density
Examples: flood, fire, pesticides, destruction of habitat, drought.
 population density: the average number of a population’s individuals that inhabit
a unit area or volume
Population size and density
Population size and density are the two most important statistics scientists use to
describe and understand populations. A population’s size refers to the number of
individuals (N) it comprises. Its density is the number of individuals within a given area
or volume. These data allow scientists to model the fluctuations of a population over
time. For example, a larger population may be more stable than a smaller population.
With less genetic variation, a smaller population will have reduced capacity to adapt to
environmental changes. Individuals in a low-density population are thinly dispersed;
hence, they may have more difficulty finding a mate compared to individuals in a higher-
density population. On the other hand, high-density populations often result in increased
competition for food. Many factors influence density, but, as a rule-of-thumb, smaller
organisms have higher population densities than do larger organisms.
Population density is negatively correlated with body size: Australian mammals show
a typical inverse relationship between population density and body size.
Population research methods
Counting all individuals in a population is the most accurate way to determine its size.
However, this approach is not usually feasible, especially for large populations or
extensive habitats. Instead, scientists study populations by sampling, which involves
counting individuals within a certain area or volume that is part of the population’s
habitat. Analyses of sample data enable scientists to infer population size and
population density about the entire population.
A variety of methods can be used to sample populations. Scientists usually estimate the
populations of sessile or slow-moving organisms with the quadrat method. A quadrat is
a square that encloses an area within a habitat. The area may be defined by staking it
out with sticks and string, or using a square made of wood, plastic, or metal placed on
the ground.
Scientist uses a quadrat to measure plant population size and density: A quadrat is
a square frame of known area in which species of interest can be easily counted and
measured.
Scientists typically use the mark and recapture technique for mobile organisms such as
mammals, birds, or fish. With this method, researchers capture animals and mark them
with tags, bands, paint, body markings, or some other sign. The marked animals are
then released back into their environment where they mix with the rest of the population.
Later, a new sample is collected, including some individuals that are marked
(recaptures) and some individuals that are unmarked.
Mark and recapture is used to measure the population size of mobile animals.: With the
mark and recapture method, researchers capture animals and mark them with tags,
bands, paint, body markings or some other sign.
Environmental Resistance and Carrying Capacity
The factors that limit the biotic potential of an organism are called environmental
resistance. These factors include abiotic and biotic factors that limit the organism from
endlessly increasing its population.
Biotic factors include predation, competition, parasitism, and diseases. Abiotic factors
include climatic conditions, fire, and temperature.
Examples of Environmental Resistance
Some of the common examples of environmental resistance include the availability of
water and predator-prey relationship.
 Water is an important resource that producers need for growth. If the producers do not
grow in an ecosystem, then the consumers in such ecosystem cannot be sustained.
 Dynamics of predator-prey populations contribute to environmental resistance. For
instance, if the predator population is low, we can expect that the prey’s population is
high.
Biotic potential and environmental resistance affect the carrying capacity, which is
defined as the maximum population of a species an ecosystem can sustain indefinitely
without being degraded due to deterioration and damage.
We can analyze an ecosystem’s carrying capacity through this graph. The carrying
capacity is the portion of the graph in which the population plateaus; this is where the
rate at which the replenished resources of an ecosystem is equal to the number of
organisms being born.
If the population exceeds the carrying capacity of its environment, it is called an
overshoot. One reason for the overshoot is when the reproductive lag time — the
time it takes for the birth rate to decrease and the death rate to increase in response to
limited resources, takes place. When this happens, a population can collapse or
dieback since there are limited resources and space unless a large number of
individuals migrate to other areas with more favorable conditions. When the population
of the organisms is below the carrying capacity, the available resources are able to
sustain the needs of the population.
Density-dependent limiting factors tend to be biotic—living organism-related—as
opposed to physical features of the environment. Some common examples of density-
dependent limiting factors include:
Competition within the population. When a population reaches a high density, there are
more individuals trying to use the same quantity of resources. This can lead to
competition for food, water, shelter, mates, light, and other resources needed for
survival and reproduction.
Predation
Higher-density populations may attract predators who wouldn’t bother with a sparser
population. When these predators eat individuals from the population, they decrease its
numbers but may increase their own. This can produce interesting, cyclical patterns, as
we'll see below.
Disease and parasites. Disease is more likely to break out and result in deaths when
more individuals are living together in the same place. Parasites are also more likely to
spread under these conditions.
Waste accumulation. High population densities can lead to the accumulation of harmful
waste products that kill individuals or impair reproduction, reducing the population’s
growth.
Photograph of a lemming. It is a small, chubby rodent that resembles a guinea pig.

Image credit: Tunturisopuli (Lemmus Lemmus) by Argus Fin, public domain
Density-dependent regulation can also take the form of behavioral or physiological
changes in the organisms that make up the population. For example, rodents called
lemmings respond to high population density by emigrating in groups in search of a
new, less crowded place to live.

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Different Biotic Potential and Environmental Resistance.

 At the end of the lesson, you should be able to describe how an

-is the maximum capacity of an individual or population to reproduce under optimal

Different factors that regulate the biotic potential of organisms:

Population size and density

Population research methods

Photograph of a lemming. It is a small, chubby rodent that resembles a guinea pig.

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