Introduction to Ecology: Understanding Ecosystems

Contributed by:
Sharp Tutor
This presentation gives an overview of Ecology defining its various components. An ecosystem consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the system through photosynthesis and is incorporated into plant tissue.
1. Introduction to
Chapter 18
2. What is an Ecosystem?
• All living organisms + the
nonliving environment in a certain
geographical location
• In other words, an ecosystem is
made up of biotic as well as
abiotic factors
• Examples: a pond, a forest, an
estuary, a grassland
3. Biotic Factors
4. Abiotic Factors
5. Abiotic factors affect living organisms in an ecosystem
Fires destroy forests, but can sometimes help a forest community by allowing
new organisms to thrive
Early or unexpected Wind can affect
frost can kill plants and the way an
an entire food chain. organism grows
6. Biotic factors affect the abiotic
factors in an ecosystem
Lichens on rocks help break them Dead organisms and animal
down into soil. Lichens are made waste contribute to soil nutrients
up of algae and fungi. (with the help of decomposers,
of course)
7. The Biosphere
• All the ecosystems of
the planet put
together, form the
8. Food
• A food chain describes
a single pathway that
energy and nutrients
may follow in an
ecosystem. There is one
organism per trophic
level, and trophic levels
are therefore easily
defined. They usually
start with a primary
producer and end with a
top predator.
• Here is an example of a
food chain:
phytoplankton →
zooplankton → fish →
squid → seal → Orca
(Killer whale)
9. Food chains always start with
• Plants, algae and certain types of bacteria
called cyanobacteria are producers
• Producers use radiant energy (sunlight) to
synthesize chemical energy (sugar)
• In other words, plants perform a complex
set of chemical reactions called
• Producers are also called “autotrophs”
which means self-feeders, because they
make their own food.
10. Primary Consumers
• Organisms that eat plants
are called primary
• Primary consumers are
herbivores – the only eat
plant material
consumers are
right above
plants in any
given food chain
11. Secondary, tertiary, quaternary
• Secondary consumers are those that eat primary consumers, tertiary
consumer secondary and so on…
• These consumers are either carnivores (sometimes insectivores or egg
eaters), or ominvores
The extinct oviraptor (egg thief)
12. Scavengers
• Scavengers are animals that do not
kill for a meal, but pick on “leftovers”
from other animals
• Hyenas, vultures, crows, racoons,
and some bears are scavengers
13. Decomposers
• Decomposers or detritivores are organisms that
degrade or decompose dead or organic material
in simpler molecules
• Fungi and bacteria are decomposers
14. FOOD
A combination of
different food chains is
called a food web.
Can you identify
all the different
organisms and
their levels?
15. Energy is eventually lost as heat on the top of the pyramid
The last level contains secondary,
tertiary consumers –
heterotrophs, carnivores,
The second level has
primary consumers –
heterotrophs, herbivores.
10% of the energy from the 1st
trophic level is available to the
2nd trophic level
The first level always
has autotrophs
90% of the energy at any given trophic level is used for growth
and reproduction, and is eventually lost as heat.
16. Matter Cycles
17. Pyramid of Biomass or
Just like energy, biomass decreases at each level, because there is only
enough energy at that level to support the biomass found there.
18. Definitions
• Habitat – where an organism lives
• Niche – the organism’s role in its
environment – what does it do for a living?
19. Symbiosis
• Organisms of different kinds living together
in the same ecosystem
• Any of the following relationships are
considered to be symbiotic:
- Predator – prey
- Parasite – host
- Commensalism
- Mutualism
- Pathogen - host
20. Predator - Prey
• Lions and zebras, for example
• One hunts and kills, the other gets killed and eaten
21. Parasite - Host
• Fleas and dogs for example
• The parasite harms the host
and benefits from the
relationship. The host is
harmed, but not usually
22. Pathogen - Host
• A pathogen is a disease-causing agent, like a
bacterium or a virus
E.coli H.I.V.
23. Mutualism
• A symbiotic relationship where
two organisms are in a mutually
beneficial relationship
• Examples: Lichens are not one
organism but two – an algae
and a fungus living as one. The
algae provides the fungus with
glucose in return for moisture
from the fungus.
Clown Fish are protected from predator
fish by the stinging tentacles of the
anemone. The anemone receives
protection from polyp-eating fish, like
Butterfly Fish, which the Clown Fish
chases away. The anemone also gets
fertilizer from the feces of the Clown Fish.
24. Commensalism
• In this relationship, one organism benefits but
the other is neither harmed nor benefited
• Examples: Shark and remora,
25. More unusual examples of animal symbiosis
26. How nutrients cycle
• Nitrogen cycle
• Carbon cycle
• Water Cycle
These are some of the various nutrient
cycles on Earth.
28. Nitrogen Cycle
29. Carbon cycle
30. Limiting Factors
• Any abiotic factor that
limits the survivability of
organisms in a particular
ecosystem is called a
limiting factor
• Examples: Water in a
desert, light in the deepest
parts of the ocean (abyssal
and benthic zones), etc.
31. Population Dynamics
• A population is defined as the number
of individuals in one particular species
in a particular place, at a given time.
For example: The population of zebras
in Kenya in the year 1980
• Population density : The number of
organisms per unit of land area or
ocean volume
32. Factors that affect population size
• Mortality
• Natality
• Emigration
• Immigration
33. Measuring the size of a population
• Census
• Sampling
• Tag and release
34. Carrying Capacity
• The maximum number of individuals of a particular species
that an ecosystem can support without depleting its resources
• These are two types of population growth curves – one shows
exponential growth (unrestricted) and the other logistic growth
35. Predator-Prey cycle
36. Boom-and-bust cycle
In species that reproduce rapidly, the population can grow exponentially
and for a brief period it can exceed the carrying capacity. After that,
there is a period of rapid decline in the population due to reduced
reproductive rate and increased death rates.