Ecology lecture 3-5 (2-2-2023), (8-2-2023).pptx

1. Course 19
Fundamentals of Ecology
Credit hour: 3(3-0)
BS Environmental Science
Semester : 4
Arbaz Madni
Lecture 3-5
NFC Institute of Engineering & Technology, Multan

2. Course Outlines:
• Describe ecological levels of organization in the
biosphere.
• Define organism, population, community, ecosystem,
biome, and biosphere as the term are used in ecology
and other ecological concepts.
• Identify factors that determine population growth
rate.
• Compare and contrast exponential and logistic growth.
• Define limiting factors and their effect on population
dynamics.

3. Population
Communit
y
Biome
Biosphere
Ecosystem
Organism A single living thing
A group of organisms of the same species that
live together.
A group of Populations that live together
Communities and their physical environments
A group of ecosystems that have the same climate.
All the biomes on Earth. Thus, all the living areas
of the planet.
Ecological Organization

4. Ecologists study organisms and their environments at different levels of
organization:
Biosphere: consists of all organisms on Earth
Biome: group of ecosystems that have the same climate and dominant
communities.
Ecosystem: consists of living things and their environment.
Community: consists of populations of different species that live in the
same area and interact together.
Population: organisms of the same species that live in the same area,
interact with one another, and produce fertile offspring.
Organisms: are individual living things.
This is the lowest level of organization that ecologists study. Biologists
study organisms, organ systems, organs, tissues, cells, organelles, and
molecules. Chemists study atoms and subatomic particles.

5. What Is a Population?
In biology, a population is a group of organisms of the same species that live in the
same area. How large a population is and how fast it is growing are often used as
measures of its health.

6. Population Growth Rate
 Population growth rate (r) is how fast a population
changes in size over time. A positive growth rate means
a population is increasing. A negative growth rate means
it is decreasing. The two main factors affecting
population growth are the birth rate (b) and death rate
(d).

7. Births and Deaths: Balancing Costs of
Reproduction and Survival
 growth rate = birth rate – death rate
r = b – d

8. If birth rate exceeds death rate, r is positive and the population
grows. If death rate exceeds birth rate, r is negative and the
population declines. And if birth rate and death rate are in
equilibrium, growth rate is zero, and the population remains stable.
In a stable population, each individual, on the average, produces one
offspring which survives long enough to reproduce itself. Mere
survival is not success in the game of life; natural selection requires
that survivors reproduce.
Species vary in the strategies they use to achieve reproductive
success, making trade-offs between the energy and time ‘‘costs” of
survival and those of reproduction.
Age at first reproduction, frequency of reproduction, number of
offspring, parental care, reproductive lifespan, and offspring death
rate are some of the traits which build strategies for successful
reproduction.

9. Other Factors Affecting
Population Growth Rate
Population growth may also be affected by people coming
into the population from somewhere else (immigration, i)
or leaving the population for another area (emigration, e).
The formula for population growth takes all these factors
into account.
 r = (b + i) - (d + e)
r = population growth rate; b = birth rate; i
= immigration rate; d = death rate; and e =
emigration rate

10. Patterns of Population
Growth
 At first, exponentially then logistically until carrying
capacity is reached

11. No population can maintain exponential growth indefinitely. Inevitably,
limiting factors such as reduced food supply or space lower birth rates,
increase death rates, or lead to emigration, and lower the population
growth rate.
In 1938, Pierre Verhulst derived a mathematical model of population
growth which closely matches the S-curves observed under realistic
conditions.
In this logistic (S-curve) model, growth rate is proportional to the size
of the population but also to the amount of available resources. At higher
population densities, limited resources lead to competition and lower
growth rates.
Eventually, the growth rate declines to zero and the population becomes
stable. The logistic model describes population growth for many
populations in nature.

12. Limits to Population Growth
 limiting factor is a property of a population’s
environment – living or nonliving – which controls the
process of population growth. Biologists have identified
two major types of limiting factors:
 Density-dependent factors
 Density-independent factors.

13. What Is a Community?
Communities are made up of populations of different species. A community is the
biotic part of an ecosystem. It consists of all the populations of all the species in
the same area. It also includes their interactions.
What Is an Ecosystem?
An ecosystem is a unit of nature and the focus of study in ecology. It consists of all
the biotic and abiotic factors in an area and their interactions. Ecosystems can
vary in size.
A lake could be considered an ecosystem. So could a dead log on a forest floor.
Both the lake and log contain a variety of species that interact with each other
and with abiotic factors.

14. Ecosystem Components
1) Niche organism’s occupation (role), where it lives,
and way in which organism’s use conditions they exist in
 Food it eats
 Place in food web
 How it gets food
 Range of temperatures needed for survival
 When and how it reproduces
2) Habitat - Physical environment to which an organisms
has become adapted and survives in.
3) Competitive Exclusion Principle - Two different species
cannot occupy the same niche in the same geographic
area. If they do they will compete with one another for
the same food and other resources. Eventually, one
species will out compete the other.

15. What Are Biomes?
A biome is a group of similar ecosystems with the same general abiotic
factors and primary producers. Biomes may be terrestrial or aquatic.
Terrestrial biomes include all the land areas on Earth where organisms live.
The distinguishing features of terrestrial biomes are determined mainly by
climate (abiotic factor). Terrestrial biomes include tundras, temperate
forests and grasslands, chaparral, temperate and tropical deserts, and
tropical forests and grasslands.
Terrestrial organisms are generally limited by temperature and moisture.
Therefore, terrestrial biomes are defined in terms of these abiotic factors.
Most aquatic organisms do not have to deal with extremes of temperature or
moisture. Instead, their main limiting factors are the availability of sunlight
and the concentration of dissolved oxygen and nutrients in the water.

16. Aquatic Biomes and Sunlight
In large bodies of standing water, including the ocean and lakes, the water
can be divided into zones based on the amount of sunlight it receives:
1. The photic zone extends to a maximum depth of 200 meters; enough
sunlight penetrates for algae and other photosynthetic organisms to
photosynthesize.
2. The aphotic zone is water deeper than 200 meters; too little sunlight
penetrates for photosynthesis to occur. As a result, food must be made by
chemosynthesis or else drift down from the water above.

17. Aquatic Organisms
Aquatic organisms generally fall into three broad groups: plankton, nekton, and
benthos. They vary in how they move and where they live.
1. Plankton are tiny aquatic organisms that cannot move on their own. They live in
the photic zone. They include phytoplankton and zooplankton. Phytoplankton are
bacteria and algae that use sunlight to make food. Zooplankton are tiny animals
that feed on phytoplankton.
2. Nekton are aquatic animals that can move on their own by ‘‘swimming” through
the water. They may live in the photic or aphotic zone. They feed on plankton or
other nekton. Examples of nekton include fish and shrimp.
3. Benthos are aquatic organisms that crawl in sediments at the bottom of a body
of water. Many are decomposers. Benthos include sponges, clams, and anglerfish
which are adapted to a life in the dark.

18. What Is the Biosphere?
The biosphere is the global sum of all ecosystems; integrating
all living beings and their relationships, including their
interactions with the elements of the lithosphere,
hydrosphere, and atmosphere.

19. Group Presentations: (Mid Term
Examinations)
 Group 1- Role of Light, soil, water, topography as
ecological factors (4 members)
 Group 2- Energy flow with in the ecosystem (3
members)
 Group 3- Structure and Function of ecosystem (3
members)

20. Marks Distribution:
 30 Mid term examinations
 50 Final term examinations
 20 Sessional Marks
3 marks for mid term group presentation,
2 marks for attendance (75% compulsory by HEC to sit in exams),
5 for Research proposal (Submission deadline after Mid term),
3 marks for final term Individual presentation,
2 marks for informed quiz,
5 marks for surprise quiz.