BIOL 4120: Principles of Ecology
Lecture 11: Species
Interaction
Dafeng Hui
Office: Harned Hall 320
Phone: 963-5777
Email: dhui@tnstate.edu
An example of species interaction: Prickly pear cactus population is
controlled by its predator, the cactus moth
Prickly pear cactus was introduced into Australia as ornamental plant,
and out of control.
Cactus month was introduced in 1920s
Now prickly pear cactus maintain a low level of equilibrium, mosaic
isolated inlands.
Species interactions
Consumer-resource interactions: fundamental ecological relationship
between species, organize biological communities into food chains;
include predator-prey, herbivore-plant, parasite-host.
Competition: two consumers share the same resource, each reduces
the availability of resources of the other.
Mutualism: interactions benefit both species (pollinator-plant)
Commensalism: benefit one, but do no harm on another (bird nests on
a tree)
Amensalism: elephant crushes a grasshopper under foot.
Topics (Chapter 14)
11.1 All organisms are involved in consumerresource interactions
11.2 Dynamics of consumer-resource interactions
reflect mutual evolutionary responses
11.3 Parasites maintain a delicate consumerresource relationship with their hosts
11.4 Herbivory varies the the quality of plants as
resources
11.5 Competition may be an indirect results of
other types of interactions
11.6 Individuals of different species can
collaborate in mutualistic interactions
11. 1 All organisms are involved in
consumer-resource interactions
Consumer-resource interactions are the most
fundamental interactions, as all nonphotosynthetic organisms must eat, and all
organisms are at risk of being eaten.
Consumer organisms: Predator, Parasite, Parasitoid,
Herbivore, Detritivore
Resource organisms: plants, animals etc
Predation


Consumption of all or part of one living organisms by another
Serve as energy transfer; Predators are agents of mortality and
feed on organisms
• Carnivory

Direct taking of animal prey for immediate consumption
• Hawk or an owl taking a mouse
• Decrease prey population, gain nutrition to support
reproduction.
• Parasitism

Predator lives in or on a host and consumes, consumers
part of a living host, but does not usually kill the host
• Ticks on mammals
• Parasites that can cause disease symptoms: pathogens
• Parasitoidism

Predator lives in or on a host and eventually kills to provide
a food source
• Parasitic wasps
• Herbivory



Consumption of whole or parts of plant material
Consumption of nuts and seeds (predator) or leaves of plants
(parasite)
Grazing (when apply to grasses and herbaceous vegetation) or
browsing (wood vegetation)
• Detritivores: consume dead organic material – such as leaf litter,
feces, and carcasses
•No direct effects on the populations that produce resource
(commensal interaction)
11. 2 Dynamics of consumerresource interactions reflect mutual
evolutionary responses
From evolution point of view, resource organisms should develop
many tactics to avoid being eaten (for consumer-resource
relationships).
Consumers (like predators) should develop better ways to hunt prey.
Plants: produce thorns and defensive chemicals that dissuade
herbivore.
Animals: hide or seek refuge in a safe microhabitats; produce foulsmelling or stinging chemical secretions (scorpions) to dissuade
predators; armored body covering (armadillos).
Boomnardier beetle sprays a noxious liquid at the temperature
of boiling water toward a predator.
Avoiding predators may result in reduced
growth rates: Bullfrog experiments by
Relyea and Werner, 1999
Grew tadpoles in aquaria with caged dragonfly larvae or fish. Fish and
dragonfly larvae are predators here.
11. 3 Parasites maintain a delicate
consumer-resource relationship with their
hosts




Parasitism: a relationship of two organisms living
together (symbiosis) and one derives its
nourishment at the expense of the other
Parasite and host
Parasitism has
• Negative effect on hosts
• But do not usually kill hosts
Parasite consists of a wide range of organisms,
including
• Virus, bacteria, protists, fungi, plants, and
invertebrates (include arthropods)
• 50% of the species on Earth (typically feed on
only one or a few host species).
Hosts provide diverse habitats for
parasites


Hosts are the habitats for parasites
Depends on the places:
• Ectoparasites: live on the skin within the
protective cover of feathers and hair
• Endoparasites: live within the host
Examples:
Fleas, ticks, are ectoparasites
Liver flukes, lung flukes, flatworms, are endoparasites
Parasite life
cycles
Many parasites
have complex life
cycles
Life cycle of the
malaria parasite
Plasmodium
Two hosts:
mosquito and
Human (or other
mammal, bird or
reptile)
Malaria: 300-500m
cases/yr, 1 Millon
died.
Parasite virulence and host resistance



Virulence: a measure of the capacity of a parasite to
invade host tissues and proliferate in them
Balance between parasite and host populations is
influenced by the virulence of the parasite and the
immune response and other defenses of the host.
Virulence can be reduced by actions of the host’s
immune system, including inflammation responses
and production of antibodies.

Inflammation response (produce certain chemical,
increase flood flow)

Immune response. White cells produce anti-body:
bind to foreign proteins, helping counter infects.
11. 4 Herbivory varies with quality
of plants as resources
Nutrient quality and digestibility of plants is critical
to herbivores.
Herbivores usually select plants according to
nutrient content, preferring young leaves (low
cellulose), fruits and seeds.

Defenses of herbivory:
 Inherently low nutrient value of most plant tissue
 Toxic compound
 Structure defenses: spines, hairs, tough seed
coats, sticky gums and resins
Digestibility: secondary compounds such as
tannin.

Secondary compounds

Three major classes based on chemical
construction



Nitrogen compound (derived from
amino acid), such as lignin, alkaloids
Terpeniods: include essential oils, latex,
and resins.
Phenolics: simple phenols have antimultimicrobial properties (carbolic
acid).

Two type of defenses

Constitutive defenses
• Fixed features of the organisms


Some type of defense chemicals are maintained at
high levels in plant tissues at all times
Induced defenses
• Defenses are brought about or induced by the
presence or action of predators, herbivores
 Chemical defense
 Behavior defense
Structure and chemical defenses protect the stems and leaves
(catus and milkweed plants) (constitutive defenses)
Induced defenses
Plant defenses can be induced by
herbivory
Mean number of the mite were
lower on cotton plants that have
previously exposed to a closed
related mite species.
Cost to produce.
11.5 Competition may be an indirect
result of other types of interactions

Direction interaction: direct relationships between two
species (e.g., predator and prey)
Consumer (+)  resource (-)
Indirection interaction:
Ex1.:
predator (+)  herbivore (-)  plant (+)
Multiple trophic levels in a food web, trophic cascade

Ex.2: Consumer 1 (+)  resource (-)  consumer 2(+)
seems like
consumer 1 (-)  consumer 2(-)
Exploitation competition or indirect competition
A competitionfacilitation continuum
Facilitation: nurse plants
Individuals of one species
facilitate the germination and
growth of a second species
An example: ironwood in
desert provides protected
sites for the establishment of
cacti (later competition for
nutrient, water and light)
11.6 Individuals of different species can
collaborate in mutualistic interactions
Mutualism: interaction benefits both species involved
honeybee and plants
(plants provide honeybee with nectar, bees carry pollen between
plants)
Can be symbiosis: lichens (algae and fungi)
or non-symbiosis: seed dispersal (birds and plants)
Could involve more species
Humans extract honeycombs (for honey)
Birds eat the wax left behind
Bacteria in the guts to digest the wax
Three categories
Trophic, defensive and dispersal mutualisms
Trophic mutualisms: feeding relationship, bacteria in rumens of cows
Defensive mutualism
Food and shelter,
defend partners
against their
consumers
Cleaning fish or shrimp
A wonderful story of Acacias plants and ants in Central America,
see textbook (298).
Some mutualists need their partners to survive and grow. Ants can’t
survive without plants; and plants can’t survive without ants.
Adaptation improved the efficiency of their association: Ants work day
and night to protect plants. Acacias retain leaves all year.
(both unusually)
Dispersive mutualism:
Birds and mistletoe
The End