BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 11: Species Lecture 11: Species InteractionInteraction

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: 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)Topics (Chapter 14)

11.1 All organisms are involved in consumer-11.1 All organisms are involved in consumer-resource interactionsresource interactions

11.2 Dynamics of consumer-resource interactions 11.2 Dynamics of consumer-resource interactions reflect mutual evolutionary responsesreflect mutual evolutionary responses

11.3 Parasites maintain a delicate consumer-11.3 Parasites maintain a delicate consumer-resource relationship with their hostsresource relationship with their hosts

11.4 Herbivory varies the the quality of plants as 11.4 Herbivory varies the the quality of plants as resourcesresources

11.5 Competition may be an indirect results of 11.5 Competition may be an indirect results of other types of interactionsother types of interactions

11.6 Individuals of different species can 11.6 Individuals of different species can collaborate in mutualistic interactionscollaborate in mutualistic interactions

11. 1 All organisms are involved in 11. 1 All organisms are involved in consumer-resource interactionsconsumer-resource interactions

Consumer-resource interactions are the most Consumer-resource interactions are the most fundamental interactions, as all non-fundamental interactions, as all non-photosynthetic organisms must eat, and all photosynthetic organisms must eat, and all organisms are at risk of being eaten.organisms are at risk of being eaten.

Consumer organisms: Predator, Parasite, Parasitoid, Consumer organisms: Predator, Parasite, Parasitoid, Herbivore, DetritivoreHerbivore, Detritivore

Resource organisms: plants, animals etcResource organisms: plants, animals etc

PredationPredation Consumption of all or part of one living organisms by anotherConsumption of all or part of one living organisms by another Serve as energy transfer; Predators are agents of mortality and Serve as energy transfer; Predators are agents of mortality and

feed on organismsfeed on organisms

• Carnivory Carnivory Direct taking of animal prey for immediate consumptionDirect taking of animal prey for immediate consumption

• Hawk or an owl taking a mouseHawk or an owl taking a mouse• Decrease prey population, gain nutrition to support Decrease prey population, gain nutrition to support

reproduction.reproduction.• ParasitismParasitism

Predator lives in or on a host and consumes, consumers Predator lives in or on a host and consumes, consumers part of a living host, but does not usually kill the hostpart of a living host, but does not usually kill the host

• Ticks on mammalsTicks on mammals• Parasites that can cause disease symptoms: pathogensParasites that can cause disease symptoms: pathogens

• ParasitoidismParasitoidism Predator lives in or on a host and eventually kills to provide Predator lives in or on a host and eventually kills to provide

a food sourcea food source• Parasitic waspsParasitic wasps

• HerbivoryHerbivory Consumption of whole or parts of plant materialConsumption of whole or parts of plant material Consumption of nuts and seeds (predator) or leaves of plants Consumption of nuts and seeds (predator) or leaves of plants

(parasite)(parasite) Grazing (when apply to grasses and herbaceous vegetation) or Grazing (when apply to grasses and herbaceous vegetation) or

browsing (wood vegetation)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 consumer-11. 2 Dynamics of consumer-resource interactions reflect mutual resource interactions reflect mutual

evolutionary responsesevolutionary 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 foul-smelling 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 Avoiding predators may result in reduced growth rates: Bullfrog experiments by growth rates: Bullfrog experiments by

Relyea and Werner, 1999Relyea 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 11. 3 Parasites maintain a delicate consumer-resource relationship with their consumer-resource relationship with their

hostshosts Parasitism: a relationship of two organisms living Parasitism: a relationship of two organisms living

together (symbiosis) and one derives its together (symbiosis) and one derives its nourishment at the expense of the othernourishment at the expense of the other

Parasite and hostParasite and host Parasitism has Parasitism has

• Negative effect on hostsNegative effect on hosts• But do not usually kill hostsBut do not usually kill hosts

Parasite consists of a wide range of organisms, Parasite consists of a wide range of organisms, includingincluding• Virus, bacteria, protists, fungi, plants, and Virus, bacteria, protists, fungi, plants, and

invertebrates (include arthropods)invertebrates (include arthropods)• 50% of the species on Earth (typically feed on 50% of the species on Earth (typically feed on

only one or a few host species).only one or a few host species).

Hosts are the habitats for parasitesHosts are the habitats for parasites Depends on the places:Depends on the places:

• Ectoparasites: live on the skin within the Ectoparasites: live on the skin within the protective cover of feathers and hairprotective cover of feathers and hair

• Endoparasites: live within the hostEndoparasites: live within the host

Examples:Examples:Fleas, ticks, are ectoparasitesFleas, ticks, are ectoparasitesLiver flukes, lung flukes, flatworms, are endoparasites Liver flukes, lung flukes, flatworms, are endoparasites

Hosts provide diverse habitats for parasites

Parasite life cycles

Many parasites have complex life cycles

Life cycle of the malaria parasitePlasmodium

Two hosts: mosquito and Human (or other mammal, bird or reptile)

Malaria: 300-500m cases/yr, 1 Millon died.

Virulence: a measure of the capacity of a parasite to Virulence: a measure of the capacity of a parasite to invade host tissues and proliferate in theminvade host tissues and proliferate in them

Balance between parasite and host populations is Balance between parasite and host populations is influenced by the virulence of the parasite and the influenced by the virulence of the parasite and the immune response and other defenses of the host.immune response and other defenses of the host.

Virulence can be reduced by actions of the host’s Virulence can be reduced by actions of the host’s immune system, including inflammation responses and immune system, including inflammation responses and production of antibodies.production of antibodies.

Inflammation response (produce certain chemical, Inflammation response (produce certain chemical, increase flood flow)increase flood flow)

Immune response. White cells produce anti-body: bind to Immune response. White cells produce anti-body: bind to foreign proteins, helping counter infects.foreign proteins, helping counter infects.

Parasite virulence and host resistance

11. 4 Herbivory varies with quality 11. 4 Herbivory varies with quality of plants as resourcesof plants as resources

Nutrient quality and digestibility of plants is critical Nutrient quality and digestibility of plants is critical to herbivores.to herbivores.Herbivores usually select plants according to Herbivores usually select plants according to nutrient content, preferring young leaves (low nutrient content, preferring young leaves (low cellulose), fruits and seeds.cellulose), fruits and seeds.

Defenses of herbivory:Defenses of herbivory: Inherently low nutrient value of most plant tissueInherently low nutrient value of most plant tissue Toxic compoundToxic compound Structure defenses: spines, hairs, tough seed Structure defenses: spines, hairs, tough seed

coats, sticky gums and resinscoats, sticky gums and resins

Digestibility: secondary compounds such as Digestibility: secondary compounds such as tannin.tannin.

Secondary compoundsSecondary compounds

Three major classes based on chemical Three major classes based on chemical constructionconstruction

Nitrogen compound (derived from Nitrogen compound (derived from amino acid), such as lignin, alkaloidsamino acid), such as lignin, alkaloids

Terpeniods: include essential oils, latex, Terpeniods: include essential oils, latex, and resins.and resins.

Phenolics: simple phenols have anti-Phenolics: simple phenols have anti-multimicrobial properties (carbolic multimicrobial properties (carbolic acid).acid).

Two type of defensesTwo type of defenses

Constitutive defensesConstitutive defenses• Fixed features of the organismsFixed features of the organisms

Some type of defense chemicals are maintained at Some type of defense chemicals are maintained at high levels in plant tissues at all timeshigh levels in plant tissues at all times

Induced defensesInduced defenses• Defenses are brought about or induced by the Defenses are brought about or induced by the

presence or action of predators, herbivorespresence or action of predators, herbivores Chemical defenseChemical defense Behavior defenseBehavior 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 competition-facilitation continuum

Facilitation: nurse plantsIndividuals 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 involvedhoneybee 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 categoriesTrophic, defensive and dispersal mutualismsTrophic mutualisms: feeding relationship, bacteria in rumens of cows

Defensive mutualism

Food and shelter, defend partners against their consumers

Cleaning fish or shrimp

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)

A wonderful story of Acacias plants and ants in Central America, see textbook (298).

Dispersive mutualism:Dispersive mutualism:Birds and mistletoe

The EndThe End