BIO 262 Resource Partitioning, Predation, + Mutualisms

Resource partitioning

ways in which species differ in their use of resources

Types of resource partitioning

I. Food: size, hardness, and type

II. Space (or habitat): 14.7-14.8

a. Broad (macrohabitat): organisms live in different ecosystems.

b. Narrow (microhabitat): organisms live in the same vegetation type but eat in different places within that habitat type.

III. Time

a. Daily: When organisms eat during the day (nocturnal, diurnal).

b. Seasonal: When organisms eat during the year (spring, summer, fall)

The ecological niche

The set of environmental conditions within which an organism can maintain a viable population

Fundamental niche:

the total range of environmental conditions that are suitable for existence IN THE ABSENCE OF interspecific competition, predation, or other interspecific interactions

Realized niche:

that part of the fundamental niche occupied IN THE PRESENCE OF interspecific competition, predation, and other interspecific interactions

Niche lab examples

I. Experiments with Paramecium (Gause): closely related species of paramecium could not coexist.

II. Gause's competitive exclusion principle: Species similar in resource use (i.e.,with identical niches) cannot coexist.

Niche in the field examples

I. Terns on Christmas Island (Ashmole) (resource partitioning by prey size)

a. Species differed in beak size and in body size.

b. The bigger the beak, the bigger the prey.

II. Warblers (MacArthur) (resource partitioning by microhabitat)

a. Species have very similar beak and body sizes.

b. Even though they appear very similar, different warbler species foragein different parts of the tree

III. Conus mollusks (Cohn) (resource partitioning by prey type and microhabitat)

a. Conus mollusks stab prey with their radula, inject toxins, and eat it.

b. Many different species coexist together.

i. Some species specialize in a few prey types.

ii. Other species feed in subtidal versus intertidal

IV. Dendrobates, the poison arrow frog (Toft 1981) (resource partitioning by prey taxon and food size)

a. Species differ in body sizes and prey types.b. Bigger frogs eat bigger prey.c. Some frogs specialize on ants, others on grasshoppers, etc.

V. Anolis lizards in Puerto Rico (Schoener) (resource partitioning by macrohabitat, microhabitat, and food size)

a. Different species in the rainforest, scrubby forest, and desert.

b. Different species inhabit tree crowns, tree trunks, and ground habitats.

c. There is also a "giant" Anolisspecies found in all of these habitats that specializes in much larger prey

How different must species be in order to coexist?

A. Limiting similarity: That degree of similarity in resource use that just allows coexistence; any greater similarity would result in one of the species becoming extinct.

B. Limiting similarity is measured in units of d/w (it is dimensionless):

I. d is the distance between the means of the curves

II. w is the standard deviation, or niche width, roughly the distance from themiddle to the side at the inflection point.

C. The niche width w tells how "fat" the curves are:

D. The shaded area (overlap here) can be visualized as related to the α of the Lotka-Volterra model: the bigger the shaded area, the bigger the α.

- More different than limiting similarity(overlap is small)

- Limiting similarity(overlap is medium-sized)

- No coexistence:species are too similar(overlap is large)

E. For Fenchel's Hydrobia mud snails (see below), d/w ≈1 when sympatric:

F. The higher the d/w, the less species compete. A d/w ≈1 is expected from some theoretical treatments. Others give less or more. Less is expected when there are predators of the competitors. More is expected when there are more species or niches are box-shaped.

Mechanisms producing resource partitioning.

A. Competitive extinction: If species are too similar, one drives the other to extinction.

B. Co-evolution: species are initially very similar to each other, but diverge over evolutionary time (thereby reducing similarity).

Evidence for limiting similarity and resource partitioning being produced by interspecific competition

A. Character displacement: species are more different from each other when in sympatry (geographic ranges overlap) than when in allopatry (no range overlap)

Predation:

Predator kills prey relatively quickly

Herbivory:

Plants eaten but generally survive

Pathogens:

Infect host, cause disease as means of reproduction/transmission

Parasitism (host/parasite):

Host is not killed quickly, but somehow exploited for its resources-can affect host's health, body weight, number or size of offspring

Endoparasites (exist inside host):

Tapeworms, liver flukes, etc

Ectoparasites (exist outside host):

Ticks, lampreys, etc

Types of ectoparasitism

I. Brood parasitism

- egg mimicry

- nestling mimicry

- mafia behavior

Brood parasitism:

Parasite lays eggs in nest of host species, host raises parasite's young

Egg mimicry:

Parasite egg looks like host spp egg (Cuckoo)

Parasite young can kill host spp young, thereby gaining a greater share of the _______ (Cuckoo & Honeyguide)

food

Nestling mimicry:

Parasite young looks like host spp young, tricking the host into feeding it (Widow-bird & Finch)

i. Most brood parasites are in the tropics - why? Possible reasons:

ii. Tropics are older, so more time for co-evolution

iii. Tropical birds are less territorial, less territorial birds are more vulnerable.

Lotka-Volterra predator-prey model (simplest)

A. Prey (victim): dV/dt = rV - aVP

B. Predator (or parasite): dP/dt = caVP - qP

V =

number of prey (food)

P =

number of predators

r =

intrinsic rate of increase of prey

a =

capture efficiency (probability that a predator-prey interaction will result in the prey being eaten)

c =

conversion constant (number of prey to make a single predator)

q =

death rate of the predators

Assumptions of the Lotka-Volterra model

A. Growth of the victim population is limited only by predation.

B. The predator is a specialist that can persist only if the victim population is present.

C. Individual predators can consume an infinite number of victims.

D. Predator and victim encounter one another randomly in a homogeneous environment.

A. Cyclic progression of V and P

B. V and P are __________ out-of-phase with one another:

oscillating

Mutualism

interactions between individuals of different species that benefit both partners; a(+,+) relationship

Mutualisms can:

A. Increase birth rates

B. Decrease death rates

C. Increase equilibrium population densities

D. Raise the carrying capacity for each species

Degree of dependence:

The necessity of the interaction for one or both partners

Obligate mutualism:

Organisms cannot survive and/or reproduce without the mutualism

- ex: pollination + termites

Facultative mutualism:

Organisms benefit from, but can survive and/or reproduce without, the mutualism

- ex: cleaner fish + marine organisms, mycorrhizae

+ plants

Degree of specialization:

The necessity of, or involvement of, one species in the interaction

Specialist:

Only two species can participate in the interaction.

- ex: I. Ant-acacia symbiosis (Janzen) + II. Comet orchid - Morgan's sphinx moth

Generalist:

There are a variety of suitable partner species.

- ex: I. Most bee-flower pollinator mutualisms. + II. Cleaner wrasses and attending fish

Benefits emerging from mutualisms

A. Trophic

B. Transport

C. Protective

D. Nutritional

E. Energetic

Trophic

mutualists rely on each other for food (Honey guides/humans)

Transport

Movement of gametes or seeds of one mutualist by another (pollination and/or seed dispersal)

Protective:

active or passive defense of one mutualist by another (gobies and shrimp...although gobies also feed the shrimp by pooping in their shared burrow. A rare counter-example to the generally-true statement that you shouldn't shit where you live)

Nutritional:

Interactions in which nutrients such as nitrogen and phosphorus are transferred from one mutualist to another (fungi in mycorrhizal symbioses)

Energetic:

Interactions in which energy obtained by one mutualist is made available to another mutualist (transfer of photosynthate from symbiotic bacteria to coral polyps)

each partner in a mutualism may get __________ types of benefits (groupers get cleaned and cleaners get food)

different

If one of the mutualistic partners dies or goes extinct, the other mutualist may still _______ in doing apparently 'irrational' things (like producing large fruits that only large [and now-extinct] herbivores can disperse)

persist

What separates mutualism from parasitism or competition?

A. The ability to reward 'friends' and punish 'cheaters'

B. Degree and type of density dependence

I. Mutualistic per-capita benefits can be independent of population density, or they can increase or decrease with population density.

II. Mutualism is different than competition--competition always increases at higher population densities