POPULATION ECOLOGY
- Population’s Size
- Growth Rate
- Density
- Population Structure
Population – It is a group of individuals of the same species living in a given area at a given time
o Population Density – Number of individuals of a species per unit area or volume
o Population size – number of individuals
o Population Distribution – It is the pattern of dispersal of individuals across an area of
interest
▪ Patterns of Dispersion – It is a way individual are spaces within the population’s
geographic range
• Clumped Pattern – Individuals are aggregated in patches
• Uniform Pattern – Often results from interactions amount the
individuals of a population and exhibits an even or homogeneous
pattern
• Random Dispersion – Population are spaced in a patternless,
unpredictable way
o Age structure
𝑁𝑎𝑡𝑎𝑙𝑖𝑡𝑦−𝑀𝑜𝑟𝑡𝑎𝑙𝑖𝑡𝑦
Population Size [Formula: ]
𝑇𝑜𝑡𝑎𝑙 𝑃𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛
o Natality – Number of individuals born each year
o Mortality – Number of individuals that die each year
o Annual Immigration – Number of individuals of a species moving into an existing
population
o Emigration – the number of individuals of a species moving out of an existing population
▪ Assume immigration and emigration balance out over time, therefore we can
define
▪ Zero Population Growth – Interval in which the number of births is balanced by
the number of deaths. So, population remains the same.
o Exponential Growth
o Biotic Potential – is the highest possible growth are and is achieved when resources are
unlimited.
o Factors
▪ Usual number of offspring per production
▪ Chances of survival age of reproduction
▪ How often each individual reproduces
▪ Age at which reproduction begins
Survivorship Curve
o Cohort – Is a term used to describe population members that are the same age and
have the same chances of surviving
o Survivorship – Is the probability of cohort members surviving to particular ages
o 3 types of survivorship curve
▪ Type 1 - Survive well past the midpoint of the life span and death does not come
until the end of the life span. Mammals e.g. humans
▪ Type 2 - Survivorship decreases at a constant rate throughout the life span;
death is usually unrelated to age. Hydras, songbirds, small mammals and some
invertebrates
▪ Type 3 - Most individuals will probably die very young. Oysters, many
invertebrates, fishes, and humans in less developed countries
Age Structure
o Pre-reproduction – 0 – 14 Years Old
o Reproduction – 15 – 64 Years Old
o Post – reproduction – 65 Above
o 3 Patterns of age structure diagram
▪ Pyramid Shaped - When the pre-reproductive group is the largest of the three
groups; the birthrate is higher than the death rate. Rapid Growth
▪ Bell Shaped - The size of the reproductive group equals the size of the pre-
reproductive group; the post-reproductive group is the smallest because of
mortality. Slow growth
▪ Urn Shaped - If the birthrate falls below the death rate, the pre-reproductive
group becomes smaller than the reproductive group; the post-reproductive
group is the largest. No growth
Patterns of Population Growth
o Population growth is equal to the number of births minus the number of deaths and
𝑑𝑁
can be expressed as: = 𝑟𝑁
𝑑𝑡
▪ If r is less than 1, then the population is shrinking.
▪ If r is exactly 1, then there is no change.
▪ If r is greater than 1, then the population is growing.
o Exponential Growth – Occurs in populations that produce offspring throughout the year
o Logistic Growth – Occurs in population that produce a single batch of offspring in a year
e.g. insects
o Carrying Capacity
▪ The maximum number of individuals is determined by the balance between the
amount of environmental goods and services that are required by each
individual and the quantity of these goods and services that are provided by the
environment.
▪ A given area of the environment is critical to the notion of carrying capacity
because the availability of environmental goods and services varies with the
type of ecosystem.
▪ Maintained Indefinitely - refers to the ability of an ecosystem to provide the
same quantity and quality of the environmental goods and services over time.
Limiting Factors of Population
o Density – Independent Factors – Are factors that affect population growth but are not
related to the size associated with weather and many of these of the population. They
are often factors are abiotic. E.g. Natural Disaster
o Density – Dependent Factors – This category includes factors that are related to
population size. E.g. Predators, parasites and pathogens
o R – Adapted Species
▪ tend to have rapid reproduction and high mortality of offspring, and may
frequently overshoot carrying capacity and die back
▪ They often tend to occupy low trophic levels in their ecosystems or to be
successional pioneers
▪ They usually do little to care for their offspring or protect them from predation
▪ They depend on sheer numbers and dispersal mechanisms to ensure that some
offspring survive to adulthood
▪ They have little investment in individual offspring, using their energy to produce
vast numbers instead
o K – Adapted Species
▪ they are usually larger, live longer, mature slowly, produce fewer offspring in
each generation, and have fewer natural predators than the species below them
in the ecological hierarchy
Population of the Philippines
o 113,955,183 as of Wednesday, July 5, 2023
o 108,149,143 (as of July 10, 2019)
o 108,450,027 as of today, September 25, 2019
o The 2019 population is 108.12 million, according to the latest UN estimates.
o 92,337,852 (2010 census) 101,717,000 (2015)
o Growth Rate: 1.72% between 2010 and 2015
o Birth rate: 24.62 births / 1000 population (2013 est.)
o Death rate: 4.95 deaths / 1000 population (2013 est.)
o Age structure: 0-14 years 34.6% (male 17,999,279; female 17,285,040)
o 65 and over 4.3% (male 1,876,805; female 2,471,644) (2011 est.)
