LAT 207: Biological Interactions in the

Environment

Kwadwo K. Mireku (Ph. D)

Dept. of Fisheries and Aquatic Sciences
OUTLINE
Definition and explanation of ecological
terminologies

Community Ecology

Abiotic factors in ecosystems

Ecological relationships and Energy flow

Ecological Succession

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Ernst Haeckel (1834 – 1919) Eugene Pleasants Odum (1912 3– 2002)
 WHAT IS ECOLOGY ?
❖Study of interactions among organisms and
between organisms and their environment
(Haeckel, 1866)
❖ It is the study of interactions between organisms
and their biotic and abiotic environment
❖Ecology is the study of structure and function of
nature/ecosystems (Odum, 1969)
❖Ecology is the scientific study of the interactions
that determine the distribution and abundance of
organisms (Kreb, 1972 & 1985)
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 WHAT IS ECOLOGY ?
❖The important concepts :
➢ The local and geographical distribution and
abundance of organisms (habitat, niche,
community).
➢ Temporal changes in the occurrence, abundance
and activities of organisms (seasonal, annual,
successional, geological).
➢ The inter-relationship between organism in
population and communities (population
ecology).
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LEVELS OF ORGANIZATION
Biosphere

Region/Biome

Ecosystem
Community
Population
Organismal
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 Levels of Organization: Species
❖ Species - Group of similarly constructed
organisms capable of interbreeding and
producing fertile offspring
❖ Various concepts on what a species is
(Read about them)

How many
species?
How many
individuals?

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 Levels of Organization: Species
❖ Species concept:
1.Typological or Essentialist Species Concept
2. Nominalistic Species Concept
3. Biological Species Concept
4. Evolutionary Species Concept.
5. Morphological species concept (MSC)
6. Ecological species concept (ESC)
7. Cohesion species concept
8. Phenetic species concept
9. Phylogenetic species concept (PSC
10. Pluralistic species concept
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 How many
species?

How many populations?

 Population ecology
❖ Population - Group of individuals belonging
to the same species that inhabit a specific
area at the same time, interbreed and
compete for resources, e.g.? food, mates,
shelter, etc
❖ Environment: refers to all the conditions
that influence and affect the development
and sustainability of life of all organisms
present on the earth.
❖ It is an immediate surrounding of living
organisms in which it lives and operates.
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 How many
species?

Kakum forest, GH

How many
populations?

Kruger park, SA
 Population ecology
• Endemic species are found only in a
particular area, e.g. kangaroos found in
Australia; kiwi of New Zealand
• Key-stone species is mostly a predator
species, which is not present in large number
but has a major influence on the
characteristics of a community, e.g. lion in the
forest.
• Critical Link species: help other species in the
vital activities, e.g. pollinators for plants, parasitic
and symbiotic relationships.
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Kiwi
Kangaroo

Koala
 Ecosystem
❖ Ecosystem - populations (plants, animals
and other organisms) in a given area,
interacting with each other, and also with the
abiotic environments
❖ E.g. terrestrial ecosystems (forest
ecosystems, grassland ecosystems, desert
ecosystems, etc.) and aquatic ecosystems
(freshwater ecosystems, brackishwater
ecosystems, coastal ecosystems, marine
ecosystems, etc.)
❖ It is the functional unit of the ecology.
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Definition of hierarchy/levels cont’d
❖ Community - different populations inhabiting a
common environment and are interdependent
❖ Could be described by:
✓Type of environment, e.g. forest community,
marine community, lake community, etc.
✓subset of populations within the bigger
community, e.g. fish community, reptile
community, mammal community, plant
community, etc.
❖ A forest community is reflection of co-
existence and interactions of a variety of
populations – trees, shrubs, herbs, grasses,
animals and microorganisms.
What ecosystem is this?
 What ecosystem is this?
How many habitats?

How will you distinguish a forest community from a

forest ecosystem?
ECOSYSTEMS: COASTAL WETLANDS

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 Mangroves

Drone image of Rhizophora species at

Sawonma Picture of Rhizophora species at New
Amanful

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Mangrove forest

Picture of Rhizophora species at Old Picture of Avicennia species at

Kablenzuazo Ampain

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Species of mangrove

Laguncularia racemosa Avicennia Rhizophora mangle Conocarpus erectus

germinans

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 BIOMES / REGION
❑ A biome is a large area characterized by
its vegetation, soil, climate, and wildlife.
❑ Generally divided into two:
• Aquatic biomes
• Terrestrial biomes
❖Aquatic biomes include:
➢Marine e.g. ocean, coral reefs, and estuaries.
➢freshwater e.g. ponds, rivers, and lakes

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 BIOMES / REGION
❖Terrestrial biomes includes:
❑ Tundra (alpine or arctic)
❑ Forests
➢Boreal coniferous forest (taiga)
➢Tropical rainforests
➢Temperate rainforest
❑ Grasslands (temperate & tropical, savanna)
❑ Deserts e.g. Sahara, Khalahari, Nubian, Namib

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Figure 1:Terrestrial Biomes
 GRASSLANDS / SAVANNAHS

GRASSLANDS:
STEPPE: Russia,
PRAIRIE,/MEADOW: North America,
PAMPAS: South America
VELDT: Southern Africa
Tussocks: New Zealand

Praire: Grassland in the USA Steppe ; Russia

 SHRUBS

Chaparral biome : shrubland in California

 BIOMES / REGION
❖ Communities have boundaries, may be very
sharp (e.g. a forest and a lake) or less sharp
(e.g. a forest and a grassland community).
❖ The transitional region between two
communities is known as Ecotone
❖ Species of both adjacent communities are
found in Ecotones, and are often richer than
either
❖ Ecotones can be natural or human induced.

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Areas of ecology
❖ Molecular ecology - the use of molecular
genetic tools (DNA) to study interactions and
diversity of natural populations
❖ Organismal ecology (autecology) - the study
of evolutionary adaptations that enable
organisms to survive in their environments -
behavior, physiology, morphology, etc. in
response to environmental challenges
❖Population ecology (autecology) – the study of
population growth and factors that affect growth
(e.g. distribution, density, natality and mortality
rates) and how members of a population
coexist.
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 Areas of ecology
❖ Community ecology (synecology) – studies
how interactions between species (competition,
predation, and symbiosis) affect community
structure and organization; as well as
ecological succession

❖ Ecosystem ecology - study of cycling of

materials and energy flow among and between
communities through ecosystem

❖ Behavioural ecology – examines the roles of

behavior in enabling an organism to adapt 34to
 Population ecology
❖ Habitat: It is a natural environment of an
organism where it grows, lives and reproduces.
❖ It is an ecological area best-suited for an
organism.
❖ It is a spatial concept
❖ Habitats vary in the physical and chemical
composition.
❖ E.g. abiotic components such as water,
temperature, light and soil and biotic
components too, e.g. parasites, competitors,
pathogens and predators
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Which habitat is this?
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 Population ecology
❖ Microhabitat: a smaller part of the habitat that
possesses specific physical conditions that
are conducive for an organism.

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 Community ecology: Niche
❖ Niche –
❖ Grinnellan niche: is the sum of the habitat
requirements and behaviors that allow a
species to persist and produce offspring
❖ Eltonian niche: The 'niche’ of an animal
means its place in the biotic environment, its
relations to food and enemies.
❖ Hutchinsonian niche: a “n-dimensional
hypervolume”, where the dimensions are
environmental conditions and resources
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 Community ecology: Niche
❖ Niche – physical space occupied by an
organism as well as its functional role in the
community - e.g. a predator, a prey, or even a
scavenger
❖ Hutchinson classified niches into:
➢ Fundamental
➢ Realized
▪ Spatial (habitat); trophic (food niche); reproductive;
multifactor**

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 Community ecology: Niche
❖Fundamental niche
❖any type of environmental condition in which a
particular species can live
❖The entire biotic and abiotic community is
available as a resource without competition.
❖Realized niche
❖environmental condition in which the species
actually live
❖the resources of the biotic and abiotic elements
are under competition.
❖Factors that control the availability of these
resources are called limiting factors
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Table 3: Difference between Fundamental and Realized niche

Condition Fundamental Realized niche

Niche
Size Large Small

Competition for No Yes

resources and
predators
Limiting factors No limiting A lot of limiting
factors factors present
Nature of niche Ideal/theoretical Actual
 Community ecology: Niche
❖ The niche-based theory states that an
ecological community is made up of a
limited number of niches, each occupied
by a single species.
❖ The competitive exclusion principle
(Gause’s law) states that in an ecosystem,
two species cannot continue to occupy the
same niche forever.
❖ Two kinds of competitions according to the
competitive exclusion principle:
• Interspecific Competition
• Intraspecific Competition 43
 Community ecology: Niche
• R* Theory and P* Theory (Read about
this!)
• Resource-ratio hypothesis
• The R* theory states that multiple species cannot
rely on the same resources and eventually will have
to differentiate their niches
• The P* theory states that consumers can coexist
when the level of resources are high due to having
shared predators
• the species that can maintain the highest consumer
density (P*) under predation will have a competitive
advantage over the other species and retain the
niche.
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INTERSPECIFIC
INTERACTIONS
❖ Symbiosis: any close relationship between
two organisms in which at least of them
benefits.
❖ Three types:
➢Mutualism
➢Commensalism
➢Parasitism
➢Competition***

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ECOLOGICAL RELATIONSHIPS
❖ Mutualism: association between organisms of
two different species in which each benefits.
❖ Obligate (necessity) or facultative (by choice)
• Eg. the partnership between nitrogen-fixing bacteria and
leguminous plants;
• cows possess rumen bacteria that live in the digestive
tract that help digest the plants the cow consumes.
• Associations between tree roots and certain fungi –
Mycorrhiza
• Lichen: algae and fungi
• Corals and zooxanthellae algae

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 What about pollination?

Sea anemone and clownfish

Zebra and oxpecker

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ECOLOGICAL
RELATIONSHIPS
❖ Commensalism: relationship between individuals of
two species in which one species obtains food or
other benefits from the other without either harming
or benefiting the latter.
❖ Larger – host; Smaller individual – commensal
❖ E.g. Shark and remora
❖ great egret (Ardea alba), that feed on insects turned
up by grazing mammals or on soil organisms stirred
up by plowing.

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Shark and pilot fish
Shark and remora

Buffalo and cattle egret

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ECOLOGICAL
RELATIONSHIPS
❖ Parasitism: relationship between two species of
plants or animals in which one benefits at the
expense of the other, sometimes without killing the
host organism.
❖ Brood parasitism (birds, wasp, fish)
❖ social parasitism (ants),
❖ sexual parasitism (uses another individual's
gametes to propagate its own genome) – Amazon
molly; deep sea fish – parthenogenesis /
gynogenesis

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Brood parasitism

Can you spot the eggs of the brood

parasite?

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A European Robin feeding a Common Cuckoo chick.

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 Sexual parasitism

A female specimen of the deep-sea anglerfish species Melanocetus johnsonii of about

75 mm in size with a 23.5 mm large male fused on her belly

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ECOLOGICAL
RELATIONSHIPS
❖ Parasitoidism: a relationship in which the parasite
always kills the host.
❖ Common with insect larvae and their hosts in which the
larva feeds upon the living host tissues in an orderly
sequence such that the host is not killed until the larval
development is complete
❖ Wasps, beetle and some worms tend to be
parasitoids

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ECOLOGICAL
RELATIONSHIPS
❖ Amensalism: is any relationship between organisms
of different species in which one organism is
inhibited or destroyed while the other organism
remains unaffected. (antibiosis and competition)
❖ eg Penicillium sp producing penicillin to prevent
growth of other bacteria (antibiosis);
❖ Cattle stepping on a grass; goat vrs beetle feeding
on grass (competition)
❖ Algae blooms
❖ Predation: one (predator) captures and feed on the
other (prey)

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 A A B
B
Scenario 2: Predation /
Scenario 1: Mutualism
parasitism

A B
A B

Scenario 3: Commensalism Scenario 4: Ammensalism

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 A B
A B
Scenario 6: Neutrality
Scenario 5: Competition

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 Community ecology: Niche

George Evelyn Hutchinson Joseph Grinnell

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TROPHIC RELATIONSHIPS:
FOOD CHAINS
• The food chain assess the transfer of energy
is through a series of organisms: each
feeding on the preceding organism
❖Each stage of the food chain is called a
trophic level
❖Two types of food chain:
▪ Grazing / predator
▪ Detritus / saprotrophic food chains
▪ Parasitic***
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 TROPHIC RELATIONSHIPS:
FOOD CHAINS
❑ Grazing food chain:
❖ First trophic level producers (e.g. green plants
and algae)
❖ Second trophic level primary consumers
(rodents & ungulates – hoofed animals); crustaceans,
copepods, molluscs
❖ Third trophic level secondary consumers
(predators, carrion feeders, parasites)
❖ Four trophic level tertiary consumers etc

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TROPHIC RELATIONSHIPS:
FOOD CHAINS
❑ In a detritus (fragments of decomposing
material) food chain:
• detritus detritivore carnivore

❖Construct a simple grazing food chain for

➢ Marine
➢ seashore
➢ freshwater
➢ terrestrial

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 FOOD WEB
❖Feeding relationships are generally more complex than
that depicted by food chains
❖In ecosystems, each organism feed on more than one
organism. Eg humans feed on plants, animals and fungi
(omnivores)
❖Many interconnected food chains make up a food web.
❖A food web shows a realistic representation of the energy
flow through different organisms in an ecosystem
❖Can you think of any example???

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A typical foodweb in the terrestrial habitat
 ECOLOGICAL PYRAMIDS
❖ An ecological pyramid is a graphical
representation of an ecological parameter, like
number or biomass or accumulated energy at
different trophic levels in a food chain in an
ecosystem.
❖ The idea of ecological pyramids was developed by
Charles S. Elton (1927), so the ecological pyramids
are also called Eltonian pyramids
❖ A given organism may occupy more than one
trophic level simultaneously.
❖ Trophic level represents a functional level.

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 1. Pyramid of Numbers
❖Here the factor that is taken into account is the
number of organisms in each trophic level.
❖As we go up the levels of the pyramid, the
number of organisms decreases.
❖The producers form the largest number and
hence are at the bottom of the pyramid.
❖Pyramids of numbers can be either upright or
inverted, depending on the ecosystem

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 A B
Can you give an example of this inverted pyramid of numbers?

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 2. Pyramid of Biomass
❑ This pyramid represents the amount of biomass of
the organisms present at each trophic level.
❑ Biomass is the weight (dry) of the organisms.
❑ It can be:
(i) Upright, e.g., in grasslands.
(ii) Inverted, e.g., in pond ecosystem, sea

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 A B

Figure : Pyramid of biomass in (a) terrestrial (b) aquatic ecosystem

 3. Pyramid of Energy
❖This is an upright pyramid that represents the flow of
energy from the producers to the final consumers.
❖Pyramids of energy are always upright since energy
decreases at each trophic level.
❖Pyramid of energy can never be inverted, because when
energy is transferred from a particular trophic level to the
next trophic level some energy is always lost as heat at
each step.
❖First law of thermodynamics (conservation of energy)
❖It represents total energy of the organisms in each
trophic level.

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Each bar in the energy pyramid indicates the amount of energy
present at each trophic level in a given time or annually per unit
area.
 Limitations of Ecological Pyramids
• (i) It never takes into account the same species
belonging to two or more trophic levels.
• (ii) It assumes a simple food chain, something that
almost never exists in nature.
• (iii) It does not accommodate a food web.
• (iv) Saprophytes are not given any place in ecological
pyramids even though they play an important role in
ecosystem.

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