Population ecology and human impact

Population Ecology and Human Impact

By : Mmatsela Kobe

- Is the study of interactions among organisms and their environment

Population Dynamics

Population:All the individuals of a species that

live together in an area

Demography:The statistical study of populations,

allows predictions to be made about how a population will change

Population Dynamics

Key Features of Populations

Population size

… is the number of individuals present at a given time.

The passenger pigeon was once North America’s most numerous bird, but it is now extinct.

Population density

… is the number of individuals per unit area.

In the 19th century, the flocks of passenger pigeons showed high population density.

Population distribution

…is the spatial arrangement of individuals.

Random- No patterns Uniform- Interactions among individuals Clumped- Often correlates with resources

Population Distribution

Changes in a Population

• factors determine population changes

1.births2.deaths3.migration

• immigration• emigration

How Do You Affect Density?

Immigration: movement of individuals into a population

Emigration: movement of individuals out of a population

Density-dependent factors: Biotic factors in the environment that have an increasing effect as population size increases (disease, competition, parasites)

Density-independent factors: Abiotic factors in the environment that affect populations regardless of their density (temperature, weather)

How Are Populations Measured?

• Population density = number of individuals in a given area or volume

• Count all the individuals in a population• Estimate by sampling• Mark-Recapture Method

Formula for capture-recapture method

Marked animals in 2nd sample = Marked animals in 1st sampleTotal caught in 2nd sample Total population size

How Do Populations Grow?

Idealized models describe two kinds of population growth:

1. Exponential Growth has no upper limit and populations grow very quickly2. Logistic Growth has a limit and growth approaches this limit in a sigmoidal fashion

Logistic growth is more realistic in real life, but exponential growth is a better model for bacterial cultures, etc. that have unlimited resources and space

Exponential Growth

• Also known as a J-curve• Growth is a fixed percentage of the whole

(e.g., 10% per day or year)• Population is growing at its full biotic

potential

• A J-shaped growth curve, described by the equation G = rN, is typical of exponential growth

– G = the population growth rate

– r = the intrinsic rate of increase, or growth rate in an ideal environment (births-deaths)

– N = the population size

Exponential Growth Curve

Logistic Growth

• Also known as S-curve• Growth slows as the population

approaches Carrying Capacity• Populations stabilize at carrying capacity

– K = carrying capacity

– The term (K - N)/K accounts for the leveling off of the curve

Logistic Growth Curve

Carrying Capacity

• Carrying Capacity (k): • The maximum population size that can be

supported by the available resources• There can only be as many organisms as the

environmental resources can support

Survivorship

• three types of survivorship curves• late loss (Type I)

• have a high survival rate of the young, live out most of their expected life span and die in old age.

• constant loss (Type II)• relatively constant death rate throughout their life span - death could be due to hunting

or diseases.• early loss (Type III)

• have many young, most of which die very early in their life.

Factors Limiting Growth Rate

• Declining birth rate or increasing death rate are caused by several factors including:

• Limited food supply• The buildup of toxic wastes• Increased disease• Predation

Reproductive Strategies

r Selection (many offspring) Short life span Small body size Reproduce quickly Have many young Little parental care Ex: cockroaches,

weeds, bacteria

Reproductive Strategies

K Selection (few offspring)

Long life span Large body size Reproduce

slowly Have few young Provides

parental care Ex: humans,

elephants

Age Distribution

• Distribution of males and females in each age group of a population

• Used to predict future population growth

Human Population Growth

• J curve growth• Why doesn’t environmental resistance take effect?

• Altering their environment• Technological advances

• The cultural revolution• The agricultural revolution• The industrial-medical revolution

Communities in Transition

• Ecological succession: process by which organisms occupy a site and gradually change environmental conditions by creating soil, shelter, and increasing humidity.

• Primary succession: community begins to develop on a site previously unoccupied by living organisms.

• Secondary succession: existing community is disrupted and a new one develops.

The Human population •World population increases every year.

•Increased population=increased needs.

•Uncontrolled population growth=problems in the avaibility of resources needed by people.

•Increase environmental damage.

•Therefore, some effort to control the population growth should be put into action in order to minimize the problems that may occur.

The Human Population

Doubled three times in the last three centuriesAbout 6,1 billion and may reach 9.3 billion by the year 2050Improved health and technology have lowered death rates

Human Impacts on Ecosystems

Habitat degradation and fragmentation

Ecosystem simplification

Genetic resistance

Predator elimination

Introduction of non-native species

Overharvesting renewable resources

Interference with ecological systems

References

• This presentation is a mash up of 5 presentations by the following:

Choudhury, S.M.(2009). Population Ecology.

http://www.slideshare.net/Shohail/population-ecology-1968004?qid=d37f2617-c106-4648-847b-08e9a5820e9b&v=default&b=&from_search=1 (Accessed on

06/03/2014).

Pointer, K. (2011).Population ecology : Populations.

http://www.slideshare.net/coachpointer/population-ecology-9976847?qid=d37f2617-c106-4648-847b-08e9a5820e9b&v=default&b=&from_search=2 (Accessed

on 06/03/2014)

Tnewberry. (2008). Population ecology. http://www.slideshare.net/tnewberry/population-ecology-514438?qid=d37f2617-c106-4648-847b-

08e9a5820e9b&v=default&b=&from_search=3.( Accessed on 06/03/2014)

Bombon, R. (2008). Population ecology. http://www.slideshare.net/gobuktaragang/population-ecology?qid=2c884cb1-1ff2-41dd-90c8-

f87a735d8bb9&v=qf1&b=&from_search=28. (Accessed on 05/03/2014).

Kesturi, A. (2013). Human population and its impact. http://www.slideshare.net/alfikesturi/7-7-human-population-and-its-impacts?qid=f2191318-2cf8-4777-

bac7-6e29c191e56b&v=qf1&b=&from_search=1. (Accessed on 05/03/2014)