Ecosystems are dynamic communities of organisms and their environment that interact. They include living elements like producers, consumers, and decomposers, as well as non-living elements like sunlight, water, nutrients and other chemicals. Scientists are concerned that human activities are exceeding environmental thresholds and disrupting ecosystems, which rely on complex interrelationships and are ultimately limited by environmental factors. Ecological succession describes how communities change over time through stages like primary and secondary succession, reaching a climax state.

1. Ecosystem
V.Santhanam
Department of chemistry
SCSVMV

2. Ecosystem
• A dynamic community of organisms living in a
particular environment and the physical
elements in that environment with which they
interact.
• Habitat: A site where a plant or animal
naturally lives and grows (within an ecosystem).
• Ecological Niche: The functional role of a
given species within an ecosystem.

3. Scientist have expressed concern that:
• Human activities are straining the natural resource
system.
• Exceeding the crucial limits called THRESHOLDS.
• Resulting in instability and usually environmental
deterioration.
Living organisms:
• Exist in nature
• In a state of balance with one another.

4. Law of Limiting Factors:
- All organisms require minimum quantity of
essentials such as nutrients, heat, light, space etc.
- The size of any population is ultimately limited
by one or more environmental factors.
• Excessive change imposes a serious threat to
existence.
• Complex web of Interrelationships.

5. Ecosystem:
• Living elements
• Non-Living elements
Living Elements:
• Producers: Plants
• Consumers: Animals
• Decomposers: Bacteria, Fungi, Insects

6. Non-Living Elements:
• Energy Source: Sun
• Chemicals: Carbon, Nitrogen, Oxygen,
Phosphorous, Hydrogen, Sulfur
– Critical components of all biological life
• Elements: Wind and Water

7. BIOGEOCHEMICAL CYCLES
• Include a variety of biological, geological and
chemical processes
• Earth as a closed system – all elements needed
for life were present when Earth formed
• Cycle through Earth’s systems – from a few days
to millions of years

8. Ecological succession
• Succession is a scientific term describing the long-term
progression of biological communities that occurs in a
given area.
• Ecological succession breaks down into three
fundamental phases: primary and secondary succession,
and a climax state.
• The study of ecological succession generally focuses on
the plants present on a particular site. But animal
populations also shift over time in response to the
changing habitat.

9. Mechanisms of succession
• F.E. Clement (1916) developed a descriptive
theory of succession and advanced it as a
general ecological concept. His theory of
succession had a powerful influence on
ecological thought. Clement's concept is usually
termed classical ecological theory. According to
Clement, succession is a process involving
several phases.

10. Stages of succession
• Primary succession
• Secondary succession
• Intermediate state
• Ecological climax

11. • Nudation: Succession begins with the development of a bare
site, called Nudation (disturbance).
• Migration: It refers to arrival of propagules.
• Ecesis: It involves establishment and initial growth of
vegetation.
• Competition: As vegetation became well established, grew, and
spread, various species began to compete for space, light and
nutrients. This phase is called competition.
• Reaction: During this phase autogenic changes affect the habitat
resulting in replacement of one plant community by another.
• Stabilization: Reaction phase leads to development of a climax
community.

12. Primary Succession
• Primary succession occurs when organisms colonize an
area devoid of life, usually after a catastrophic natural
event that leaves the land barren.
• Often the first organisms to take hold are algae, fungi
and simple plants such as lichens and mosses.
• Over time a thin layer of soil builds up so that more
advanced plants, such as grasses and ferns, can take
root.
• Along with the successful colonization of plants come
animals such as insects, birds and small invertebrates.

13. Secondary Succession
• Most ecological change occurs as secondary succession.
In fact, most biological communities are in a continual
state of secondary succession.
• This term describes the process in which an established
community is replaced by a different set of plants and
animals.
• Secondary succession is gradual, always moving toward
the climax community.
• Most ecosystems, however, experience disturbances --
either natural events such as wildfires or flooding, or
man-caused events such as logging -- that set back the
progress of succession.

14. Intermediate Stages
• An ecosystem undergoes many intermediate stages of
succession. These changes form a continuum between
the two endpoints, with the actual stages being merely a
fixed glance at the never-ending progression of plants
and animals.
• The emergence of the climax state of succession may
occur more quickly in some ecosystems, and likely
never occur in other biomes that experience routine
disturbances.
• Examples of quickly forming climax communities are
the short-grass and long-grass prairies

15. • A seral community is an intermediate stage found in an
ecosystem advancing towards its climax community.
• In many cases more than one seral stage evolves until
climax conditions are attained.
• A prisere is a collection of seres making up the
development of an area from non-vegetated surfaces to
a climax community. Depending on the substratum and
climate, a seral community can be one of the following.

16. • Hydrosere
– Community in freshwater
• Lithosere
– Community on rock
• Psammosere
– Community on sand
• Xerosere
– Community in dry area
• Halosere
– Community in saline body (e.g. a marsh)

17. Climax Communities
• Climax communities are relatively stable and can vary
widely in a given region, especially when the landscape
consists of high mountains and low valleys.
• In such cases, the final biological matrix of plants and
animals can cover vast tracts of land or be limited to a
very small pocket within the landscape.
• Overall, a climax community is very dependent on
rainfall, soil, altitude and temperature.

18. Biomes
• A biome is the largest terrestrial ecological unit
• Characterized by interaction of flora and fauna
and abiotic factors.
• The land mass is divided into different biomes
according to location, temperature and rain fall.
• A biome is getting the name from the
dominating /climax plant form. Ex grass biome
is where grasslands predominates.