Interspecific competition 

May be a result of exploitation of resources or of direct interference. Give an example of each and compare their consequences for the species involved.

How do the fundamental and realized niche concepts help us to understand the effects of interspecific competition.

1) Even if there are two shared resources, two species could either have enough of the resource to each have a realized niche, or if one resource is more plentiful the superior competitor will exclude the other species.

2) If two competing species coexist in a stable environment, then they do so as a result of niche differentiation of their realized niche.

3) potential competitors that coexist in a community should exhibit niche differentiation.  This will manifest itself as morphological differentiation.

4) Within a community, potential competitors with little or no niche differentiation should not coexist, so each should tend to occur only where the other is absent.

What is the “ghost of competition past?

Why is it impossible to prove an evolutionary effect of interspecific competition?

  Meriones vs Gerbalis

Ecologists want to know what is governing the distribution of species.

Mariones

- Fundamental niche is in N-dunes and inland

- realized niche in S-inland

Possible experiment:

Remove gerbillus from the dunes and Mariones fail to colonize the dunes where gerbillus was removed.

Why? Perhaps past competition led to niche partitioning.

Provide one example each of niche differentiation involving physiological, morphological and behavioral properties of coexisting species. How may these differences have arisen?

Exponential Growth formula: 

Logistic Growth formula:

G=(r)N(pop)

G=10(1)=(10+1)=11

Three types of predators?  Characteristics?

True Predators

Grazers

Parasites

Intraspecific (density dependent)

- predation

- grazing

- disease

True predators, grazers and parasites can alter the outcome of competitive interactions that involve their prey populations: discuss using one example from each category.

Grouses principle of Competitive Exclusion. 

if two competing species coexist in a stable unchanging environment, they do so as a result of niche differentiation (partitioning). If there is no such partitioning (differentiation), one species will exclude the other.

Inter-specific Competition

individuals of one species suffer a reduction in fecundity, survivorship or growth as a result of exploitation of resources or interference by individuals from another species, affect the pop dynamics of the competing species, influencing the species distributions and evolution.

The Lotka-Volterra mathematical model of inter-specific competition:

Two competing species:      N₁, N₂, K_1, K₂

r₁, r₂

Competition coefficient links them together.  Inhibitive effects of species 2 on species 1

You can define carrying capacity arbitrarily to play w/model:

dN₁/dt= r₁ N₁ (K₁ -N₁ –(fish)₁₂ N₂/K₁)

dN₂/dt= r₂ N₂ (K₂ –N₂ –(fish)₂₁ N₁/K₂)

Verbal result of model: According to LV model of inter-specific competition, two species coexist stably ONLY when intra-specific competition exceeds inter-specific competition. If opposite, one species will exclude the other species.

Capled Oscillations

Discuss the various ways that plants may compensate for the effects of herbivory.

With the help of an example, explain why most prey species may be found in communities subject to an intermediate intensity of predation.

Econcern: Forest Tent Caterpillars

Disease Dynamics and Cycles

tendency for predators and prey to exhibit cycles in abundance.

- Crowding of either predator or prey is likely to have a damping effect on any predator-prey cycles.

- Many possibilities of pred/prey exist as a metapopulation, asynchrony and dispersal in population dynamics tend to dampen underlying pop cycles.

Define characteristics of Parasitism

lives on host, but doesn’t kill it.

The cuckoo is a parasite larger than its host (parasites live off of income) Parasites have a type III mortality rate

Scramble Competition

whichever got to the resources first and starts growing first will keep the resource from others.

Allelopathy

Interference competition (regular pattern) such as scrub jays and their piece of earth or a chemical in plants

The Niche

profession (how you fit in your world and what you do). The sum total of all environmental factors affecting fitness in population of a species.

The Habitat

is your address

Brachycentrus Americanus (catisfly) are filter feeders

Struggle for existence

Competition among plants, “self thinning rule”

Low density high per capita biomass/

high density low biomass

Obligative

Facultative

Mutualism

Mutualism is not necessarily 50/50 but is usually beneficial to two unrelated species.

Obligate Mutualism

Both partners require each other.

example:

In Cleveland exposed lab termites died as if they’d starved. 

- They survived if trophallaxis feeding was permitted (feeding from the rear end the microbes from other termites).

Ecocern Etopic: Mojave desert, new exotic plants crowd out native plants and provide fuel for flames to damage the delicate ecosystem. Charred creosote bushes dot the mesa where there hadn’t been a fire in 1000 years. There usually isn’t a lot of fuel for a fire b/c vegetation is so sparse. Now the grasses are everywhere and choking out the wildflowers and killing off shelter and food that they rely on. Esque of the USGS  roped off 12 experimental sites and burned six in 1999 to see how quick invasive species re-establish themselves. The results showed unpredictability and he was left uncertain as to whether he was looking at co-existence or competition.

Coevolution

Classic Case

Parasite: myxoma virus

Host: rabbit

Fenner et al established strains/lines of myxoma virus to control the rapid spread of rabbits.  In 1951, myxoma was released inAustralia. The virus evolved over time and then stabilized around grade III. Rabbits also evolved by responding to the virus. The early release virus was too weak and couldn’t carry in the mosquitoes to the rabbits. Perhaps the strongest virus was to strong and killed the mosquitoes?

Rp: SBL

Rp: mean number of new infections from a single infected individual in a population of susceptible hosts.

S: number of susceptible hosts

P: transmission rates

L: latency, mean period of time over which the infected host remains infections.  If any of the factors go up then Rp goes up

When Rp is <1, disease dies off

When Rp is >1, disease spreads

When Rp=1, transmission threshold is met (balanced)

We can assume that if: 1=SBL, then SBL=1, and S_t=1/BL (S_t defined as a critical population threshold size)

S_t = 300,000 (approx) critical threshold for measles

Parasites evolve to be nice to their hosts unless the population is big enough so that the virus can hop from person to person, even if it kills the host.

Genet 

Anthropogenic

Disturbance

A discreet event that occurs over time ultimately disrupting a community. 

Coevolution of parasites and hosts

Example:

Plague of rabbits infected australia because 12 pairs of placentals were introduced for sport.

Pathogens can be lethal if the host population is large enough.

The pocket gopher acts as a mediator in plant communities. It can mediate competition between species of plants. It churns, digs and burrows allowing new species to pop up.

Gall sharing

A function of foundress (gall inducers) density. It is costly to individual foundresses. Hypothesis: kinship mediates costs and benefits of sharing galls. Prediction: foundresses sharing galls likely to be clones.

When gall-inducers are clone-mates, any pay-offs for sharing galls go to a single genotype (clone mate is an animal with same genotype).

When gall-inducers are unrelated, gall inducers are acting selfishly and suffer reduced fitness on a per capita basis.

When all inducers are shoved in a space overall fitness is reduced for all. Even if each animal takes a hit, the whole genotype benefits.

“Arms Race”

Coevolution of predators and prey

Example: fox is hungry and chases hare, response hare is faster, fox must become faster, hare becomes faster

This is a positive feedback loop, one species is exerting pressure on another species.

Evolutionary Ecology

Example: Acorns, Lyme Disease:

Outstanding problems in molecular ecology:

- differ between species and populations, e.g., carris spp.

maternity/paternity analysis to reveal kinship.

- forensic applications in the protection of endangered taxa, e.g., salmon.

- Distinguishing clonal and sexual reproduction.

Two species that look the same but are not the same via DNA (like siblings).

Ch8: 5

Account for the decline in virulence of the myxomatosis virus in European rabbits after its initial introductions in Australia and Europe.

Ch9: 2

Population census data can be used to establish correlations between abundance and external factors such as weather. Why can such correlations not be used to prove a causal relationship that explains the dynamics of the population?

Fundamental Niche: (in the absence of competition): combinations of conditions and resources that allow a species to exist, grow and reproduce when considered in isolation from any species that might be harmful to it. All the values of n (undefined, n-dimensional hypervolume) environmental factors.

- Even in a location providing a fundamental niche, one species may be excluded by another that denies it a realized niche there.

True predator

Invariably kill their prey and do so more or less immediately after attacking them; consume several or many prey in the course of their life.

Attack, eat or ingest more than 1 prey item but they don’t usually kill them. Grazers live off of income.

Parasites:  consume only part of each prey item (host); do not usually kill their prey; attack one or vry few prey items in the course of their life.

Parasatoid: destroys the host from the inside out.

macro parasites: grow w/in host but multiply outside the host, be releasing tapeworms, proglotids (infective stage).

Micro parasites: bacteria, fungi protozoans (malaria) grow w/in host and multiply directly w/in the host, pathogenic (cause illness or symptoms in the host)

Obligate Species

Reciprocal Exploitation Mycorrhizae

fungi living on the roots of plants, fungi gets carbs from plant, plants get water from hydrofungi, gains fungal nitrogen and phosphorus.

Arbuscular mycorrhizae

- genus glomas associated w/95% of vascular plants.

Plants obtain 75% of their required nitrogen for 15% of their carbon.  Fungi obtain 100% of their carbon for 40% of their nitrogen.

non-seasonal, directional, and continuous pattern of colonization and extinction. Species in a community following a disturbance. New species show up old species disappear.

Introduced competition

limited by abiotic factors

- desiccation

Environmental heterogeneity in time and space mediate outcome in interspecific competition

Ch8: 6

Compare and contrast the mutualistic associations of ants with plants they protect and aphids they farm.

Ch8: 10

Leguminous plants are a perfect example of a mutualistic association that can only be understood in the context of the ecological community within which it normally exists. Discuss.

Ch9: 5

What is meant by a "metapopulation" and how does it differ from a simple population?

Ch9: 6

Define founder control and dominance control as they apply to community organization. In a mosaic of habitat patches, how would you expect communities to differ if they were dominated by founder or dominance control?

Ch9: 7

What factors are responsible for changes in species composition during an old field succession?

T or F

The fundamental niche of a species is the realized niche, restricted by the presence of competitors.

T or F

Most natural environments are not subject to disturbance and have reached a state of climax or equilibrium.

T or F

The realized niche is the combination of conditions and resources that allows a species to exist, when considered in isolation from other species acting as competitors or natural enemies.

T or F

The fossorial (digging) activities of pocket gophers can mediate th.4e coexistence of colonizing vs competitive species of plants?

T or F

Gause's competitive exclusion principle states that two species with identical reqs for existance cannot coexist indefinitely.

T or F

Host population sizes equal to the critical pop size. S_t tend to favor the spread of pathogens among susceptible hosts in a given population.

T or F

Counting the number of clonal subunits (ramets) in a pop of asexual organisms such as aphids tends to underestimate the number of evolutionary individuals (genets).

T or F

In a bizarre example of parasite manipulation of host behavior, the horse-hair worm, a nematomorph is capable of inducing its intermediate host, a cricket, to swim. Once the cricket jumps in the water, the worm exits the cricket's body to compete its life cycle, having consumed most of the cricket's internal tissues. The cricket then dies.

T or F

According to the Lotka-Volterra model of competition, two species coexist stably only when the strength of intraspecific competition exceeds that of interspecific competition.

T or F

In secondary succession of old fields to forest, species richness tends to reach its peak during the climax phase.

T or F

Saguaro cactus facilitates the establishment of palo verde shrubs