FUNDAMENTALS OF ECOLOGY
BIO212
Derrick Banda MSc, BSc
How to get a hold of Derrick Banda
• Office: Mulungushi University Main Campus SSET
Offices
• E-mail: dbanda@mu.ac.zm dbanda45@yahoo.com
• Phone Number:0974420585, 0955556060
POPULATION ECOLOGY
WHAT IS POPULATION?
• A population is a group of individuals of the same
species that occupy a specific area over a certain
period of time.
WHAT IS POPULATION ECOLOGY?
• Population Ecology is the ecological study of how
biotic (living) and abiotic (non-living) factors
influence the density, dispersion, and size of a
population.
• Population ecology includes studying environmental
influences on population density and distribution,
age structure, and variations in population size
• In population ecology a population is a group of
individuals of the same species inhabiting the same
area.
POPULATION SCALE
• Populations can be considered at a scale of regions,
islands, continents or seas. Even the entire species
can be viewed as a population.
POPULATION SCALE
• The focus of ecological studies occurs at many
different scales.
Organismal ecology
Population ecology
Community ecology
Ecosystem ecology
Landscape ecology
Global ecology
POPULATION DYNAMICS
• Population dynamics refers to how populations
of a species change over time.
• The study of a species’ population dynamics usually
seeks to answer questions such as:
1. What explains average abundance of a population?
2. What causes fluctuations in abundance?
POPULATION DYNAMICS
• Three(3) key features of Populations
1. Size
2. Density
3. Dispersion
POPULATION SIZE
• Total Population size is generally expressed as the
number of individuals in an area.
POPULATION GROWTH
• First, population size is influenced by the per capita
population growth rate, which is the rate at which
the population size changes per individual in the
population.
• The growth rate in a population is determined by:
1. Birth (natality) and Death (mortality ) rates
2. Emigration and migration rates
• When the per capita growth rate remains constant, the
population can experience exponential growth followed
by exponential decline.
POPULATION GROWTH
• Within any population, individuals are born and individuals die.
• If there are more individuals being born than dying, the
population grows in size, while if more individuals are
dying than being born, the population shrinks.
• Individuals may also enter or leave a population, which is
referred to as immigration and emigration.
HOW DO POPULATIONS GROW?
• Idealized models describe two kinds of population
growth:
a) Exponential Growth
b) Logistic Growth
EXPONENTIAL GROWTH
• When resources are unlimited, populations exhibit
exponential growth, resulting in a J-shaped curve.
• Used in order to understand the capacity of species for
increase and the conditions that may facilitate this type
of growth.
EXPONENTIAL GROWTH OF
HUMAN POPULATION
• Human population may reach 9.3 billion by the year 2050
• Improved health and technology have lowered death rates
• J curve growth
LOGISTIC GROWTH
• When resources are limited, populations exhibit
logistic growth.
• In logistic growth, population expansion decreases
as resources become scarce. It levels off when the
carrying capacity of the environment is reached,
resulting in an S-shaped curve.
CARRYING CAPACITY
• As a population grows in an area, a population may
experience the effects of increased densities.
• In a given area, the maximum population size of the species
that the environment can sustain is called the carrying
capacity.
• Carrying capacity is determined by the amount of
available resources (food, habitat, water). There can only be
as many organisms as the environmental resources can
support.
• As the density of individuals in a population increases, these
individuals must begin competing for limited resources with
each other (same species, or intra-specific competition) or
with other species (inter-specific competition).
Carrying capacity and exponential versus
logistic population growth
• In an ideal environment populations grow at an exponential rate. The
growth curve of these populations is smooth and becomes
increasingly steep over time (left). However, for all populations,
exponential growth is curtailed by factors such as limitations in food,
competition for other resources, or disease. As competition increases
and resources become increasingly scarce, populations reach the
carrying capacity (K) of their environment, causing their growth rate
to slow nearly to zero. This produces an S-shaped curve of population
growth known as the logistic curve (right).
POPULATION DENSITY
• Population density is defined as the numbers of
individuals per unit area or per unit volume of
environment.
• The number of people or organisms living per unit of
an area (e.g. per square mile); the number of people
relative to the space occupied by them.
• How full an area is: the concentration of people or
things within an area in relation to its size.
Population Density = # of individuals ÷ unit of space
POPULATION DENSITY
• Density is the result of a dynamic interplay
– Between processes that add individuals to a
population and those that remove individuals from it.
POPULATION DENSITY
• Population density measures the number of individual
organisms living in a defined space
High Population Density at China’s Qingdao Huiquan Beach
POPULATION DISPERSION
• Dispersion is the pattern of spacing among individuals
within the boundaries of the population.
• In nature, due to various biotic interactions and
influence of abiotic factors, the following three basic
population distributions can be observed:
a) Clumped dispersion: Organisms that live in colonies, herds, flocks,
or packs have a clumped dispersion pattern.
b) Uniform dispersion: Organisms that are solitary and/or territorial
often have a uniform dispersion pattern. (bear or wolverine)
c) Random dispersion: Organisms that are not very territorial or do
not live in big groups tend to have a more random dispersion.
(snowshoe hare)
POPULATION DISPERSION
POPULATION GROWTH REGULATION
• Population regulation is a density-dependent
process, meaning that population growth rates are
regulated by the density of a population.
• No population can increase without limitation.
Instead, populations in natural ecosystems increase
or decrease in response to the changes in the
factors that restrict growth.
FACTORS AFFECTING POPULATION
SIZE AND GROWTH
• Many factors influence population densities and
growth, and these factors may lead to oscillations in
population size over time.
• It is also often difficult to determine the exact
factor limiting growth. Many different factors may
combine to produce unexpected results.
FACTORS AFFECTING POPULATION
SIZE AND GROWTH
• The population's growth is influenced by two main
factors–
1. Density-dependent factors, in which the
density of the population at a given time affects its
growth rate.
2. Density-independent factors, which influence
growth rate of the population regardless of its
population density.
DENSITY-DEPENDENT FACTORS
• In population ecology, density-dependent processes occur when
population growth rates are regulated by the density of
a population.
• Most density-dependent factors, which are biological in nature
(biotic), include predation, competition, accumulation of waste,
and diseases such as those caused by parasites.
• Usually, the denser a population is, the greater its mortality rate.
• For example, during intra- and interspecific competition, the
reproductive rates of the individuals will usually be lower,
reducing their population’s rate of growth.
• In addition, low prey density increases the mortality of its
predator because it has more difficulty locating its food source.
DENSITY-DEPENDENT FACTORS
1. Competition
 Food and water
 Habitat/space
 Sunlight
 Mating (Concerns relate to genetic mutations, and the number
of individuals competing for a mate.)
2. Spread of Disease: Overcrowding increases the possibility of
diseases being spread in a population.
3.Predation: Overcrowding interferes with the natural predatorprey relationship in an ecosystem.
4. Parasitism: Overcrowding
DENSITY-INDEPENDENT FACTORS
• They are limiting factors that occur regardless of how large the
population is and reduce the size of all populations in the area; mostly
abiotic.
• These density-independent factors include food or nutrient limitation,
pollutants in the environment, and climate extremes (weather and
temperature changes).
• In addition, catastrophic factors can also impact population growth,
such as fires and hurricanes. An individual deer may be killed in a
forest fire regardless of how many deer happen to be in that area. Its
chances of survival are the same whether the population density is
high or low.
• The quality of nutrients (e.g., food quality, amount of particular plant
nutrients) in an environment affects the ability of an organism to
survive, grow, and reproduce.
EFFECTS OF COMPETITION ON
POPULATION SIZE AND GROWTH
• Ecological competition is the struggle between
two organisms for the same resources within an
environment.
• If two species compete for a resource, the result
may be a reduction in the number of either
species or the elimination of one of them.
• More often, one species will be able to use a
resource more efficiently than the other. As a result,
less of the resource will be available to the other
species.
EFFECTS OF COMPETITION ON
POPULATION SIZE AND GROWTH
• The effects of one species upon another that derive from these
interactions may take one of three forms: positive (+), negative
(–), and neutral (0). Hence, interactions between any two
species in any given biological community can take any of six
forms:
1. Mutualism (+, +), in which both species benefit from the interaction.
2. Exploitation (+, –), in which one species benefits at the expense of the
other.
3. Commensalism (+, 0), in which one species benefits from the interaction
while the other species neither benefits nor suffers.
4. Interspecific competition (–, –), in which both species incur a cost of
the interaction between them.
5. Amensalism (–, 0), in which one species suffers while the other incurs no
measurable cost of the interaction.
6. Neutrality (0, 0), in which both species neither benefit nor suffer from
the interaction.
EFFECTS OF COMPETITION ON
POPULATION SIZE AND GROWTH
• Competitive ecological interactions can be1. Intraspecific competition, between individuals
belonging to the same species.
2. Interspecific competition between individuals
of different species.
COMPETITIVE INTERACTIONS
1. Competition-Ecological competition is the
struggle between two organisms for the same
resources within an environment.
i. Interspecific
ii. Intraspecific
• The intraspecific competition is between
individuals belonging to the same species, and
interspecific competition is between individuals
of different species.
COMPETITIVE INTERACTIONS
• The intraspecific competition is between
individuals belonging to the same species. For
Example, two Eagles competing for the one fish.
COMPETITIVE INTERACTIONS
• Cheetahs are highly territorial
– Using chemical communication to warn other
cheetahs of their boundaries is an example of
intraspecific competition.
COMPETITIVE INTERACTIONS
•
Interspecific competition is a type of interaction in
which two or more species use the same limited
resource. For Example, both lions and hyenas compete
for prey such as zebras.
EFFECTS OF COMPETITION ON
POPULATION SIZE AND GROWTH
• Another extinction on ecological competition can
be1. Exploitation competition, in which the actions
of one species (or individual) reduces the
availability of a resource to another species and
individual.
2. Interference competition, in which the actions
of one species (or individual) actively interferes
with the abilities of another to use a resource.
EXPLOITATION AND
INTERFERENCE COMPETITIONS
EFFECTS OF PREDATION ON
POPULATION SIZE AND GROWTH
• PREDATOR-PREY INTERACTION
• Predation is any interaction between two species in which
one organism is killed and devoured.
• There are a couple of ways in which predator-prey
interactions can influence population size and growth:
1. Predators that rely on specific prey are restricted by the
population size and growth of the prey.
2. Predators may limit prey’s population size and growth by
killing and eating prey organisms.
EFFECTS OF PREDATION ON
POPULATION SIZE AND GROWTH
• In predation, an individual of one species, called
the predator, eats all or part of an individual of
another species, called the prey.
Many types of organisms can act as predators or prey
EFFECTS OF PREDATION ON
POPULATION SIZE AND GROWTH
• Sometimes prey’s population may be affected when
predators are introduced into areas where they do not
normally occur. This may be deliberate – a form of
biological control of a pest species.
• The introduction of the huge Nile perch (Lates niloticus)
into Africa’s Lake Victoria resulted in the extinction of many
species native to Lake Victoria.
NICHE THEORY AND COMPETITION
• A species' niche is basically its ecological role, which
is defined by the set of conditions, resources, and
interactions it needs (or can make use of).
• Each species fits into an ecological community in its
own special way and has its own tolerable ranges
for many environmental factors.
• For example, a fish species' niche might be defined
partly by ranges of salinity (saltiness), pH (acidity),
and temperature it can tolerate, as well as the types
of food it can eat.
NICHE THEORY AND COMPETITION
• Two organisms with exactly the same niche can't
survive in the same habitat (because they compete
for exactly the same resources, so one will drive the
other to extinction).
• However, species whose niches only partly overlap
may be able to coexist. Also, over long periods of
time, they may evolve to make use of more different,
or less overlapping, sets of resources.
NICHE AND COMPETITIVE EXCLUSION THEORY
• The competitive exclusion principle tells us that
two species can't have exactly the same niche in a
habitat and stably coexist. That's because species
with identical niches also have identical needs, which
means they would compete for precisely the same
resources.
• In nature, it's rarely the case that two species
occupy exactly identical niches. However, the
greater the extent to which two species' niches
overlap, the stronger the competition between
them will tend to be.
NICHE AND COMPETITIVE EXCLUSION THEORY
• A famous example of the competitive exclusion principle is shown in
the figure below, which features two types of single-celled
microorganisms, Paramecium aurelia and Paramecium caudatum. When
grown individually in the lab, both species thrive. But when they are
grown in the same test tube (habitat) with a fixed amount of
nutrients, both grow more poorly and P. aurelia eventually
outcompetes P. caudatum for food, leading to P. caudatum's extinction.
QUESTIONS??
1. What environmental factors stop a population
from growing?
2. Why do some populations show radical
fluctuations in size over time, while others remain
stable?
END OF LECTURE!
THANK YOU.