FUNDS 4

Competition?

Is an interaction between two or more organisms using the same limited resource.

Competition often occurs when fundamental niches overlap

Resource?

anything an organism consumes or uses that causes an increase in population growth rate when it becomes more available.

The role of resources?

Ecological factors that cannot be consumed, and thus monopolized, (e.g., temperature) are not considered resources.

Resources for plants can include sunlight, water, and soil nutrients.

Resources for animals can include food, water, and space.

Exploitative competition?

Resource competition

Competition in which individuals consume and drive down the abundance of a resource to a point that other individuals cannot persist

Indirect competition because it occurs through a shared resource

Interference competition?

when competitors do not immediately consume resource but defend them, preventing establishment of a competitor

Direct competition because it is an interaction directly with the competitor

Types of interference competition?

Allelopathy (only plants)

Territoriality (only animals)

Preemption

Allelopathy?

a type of interference competition that occurs when organisms use chemicals to harm their competitors

Allelopathy can be an effective strategy for invasive plants

Plants

Preemption?

A type of interference competition determined by who finds and occupies a place first

Territoriality?

Active defense of a resource that excludes other organisms

Animals

Niche?

The constellation of environmental conditions under which a species can survive and reproduce

Often considered a multi-dimensional box that defines the limits to survival for each environmental factor (i.e. each dimension)

Any environment that falls within the multi-dimensional "space" defined by the niche can potentially host the species.

Factors of niche?

temperature, rainfall, nutrient levels, and so on.

They might also include requirements such as the existence of nesting sites

Fundamental Niche?

Complete set of environmental conditions in which the species can potentially survive and reproduce.

This includes both abiotic factors like temperature and precipitation as well as biotic factors like food availability

Realized Niche?

The set of environmental conditions in which the species is actually found in nature.

A subset of the species' fundamental niche

Restricted by BIOTIC interactions (i.e., interactions with other living things

BIOTIC interactions?

Competition

Predation

Parasitism

The realized niche is restricted by biotic interactions

Competition?

Competition results in a negative effect on all parties involved

Even when one party “wins”, they would have gained more of the resource if competition were not there in the first place

Competition interactions?

(-/-)

Predation interactions?

(+/-)

Amensalism interactions?

(-/0)

Mutualism interactions?

(+/+)

Commensalism interactions?

(+/0)

Intraspecific competition?

Intra = within

Competition among members of the same species

often the result of density-dependent effects

High densities result in limited resources

Interspecific Competition?

Inter = between

Competition between members of different species

Competition: related species?

Darwin suggested that competition is most intense between related species because they have similar traits and consume similar resources

For related species that compete strongly, natural selection should favor differences in habitat use.

Predation and herbivory?

There are often trade-offs between competitive ability and resistance to predators or herbivores; the most competitive organisms are often the most susceptible to predation or herbivory.

Thus, the presence of predators can reverse the outcome of competition.

Other types of interspecific interactions?

Mutualism

Commensalism

Ammensalism

Competitive exclusion principle?

No two species can coexist in the same niche

If two species are using the same resource, one would win and outcompete the other

Resource partitioning?

species after their use of the niche to avoid competition, by dividing resources among them

Exemption to Competitive exclusion principle?

The competitive exclusion principle does not hold up in all situations

Paradox of plankton: many species of plankton appear to coexist within a single niche (competing for the same resources: light and few nutrients)

Don’t know why

What can’t be a resource?

Things that can’t be consumed or monopolized

Temperature

Two predators consume the same prey species. Because each predator reduces the availability of this prey organism for the other, we can refer to the interaction between the two predators as one involving __________.

Competition (-/-)

What type of population growth would intraspecific competition result in?

Logistic

Can competition lead to adaptation by natural selection?

Yes

Common garden experiment?

Experiment of growing two organisms together with manipulating resources to see the presence of competition

What can alter competitive interactions?

Disturbances

Predation and Herbivory

Interactions

Consumer?

predator, parasite, or herbivore

Resources?

Prey or food?

Predators?

Consumer of animals

Herbivores?

Consumer of plants

Grazers?

eat herbaceous plants (grass, forbs, herbs)

Browsers?

eat woody plants

Granivores?

eat seeds

Frugivores?

eat fruit

Browsers/grazers and the cellulose problem?

Fruits and seeds are high quality foods, but grasses and woody plants are primarily made of cellulose which mammals can’t digest (we lack the appropriate enzyme).

Browsers/grazers and the cellulose problem: Mammals will often?

Target young plants and new growth, because they have lower cellulose content.

Increase mechanical digestion time (e.g., “chewing cud”).

Mutualistic associations with symbiotic microorganisms that have cellulose digesting enzymes.

Endoparasites?

internal parasites

Harder to detect and remove

Inside organs, lack of protection

Ectoparasites?

external parasites

Easier disease transmission

Why is it harder to treat most parasite infections than bacterial infections?

Parasites are usually eukaryotes, like humans.

Bacteria are prokaryotes (no membrane-bound organelles).

Difficult to create medicine that just targets parasites (not us also)

Consumer-resource dynamics?

Populations of consumers are self-limited

Populations of resources are limited by consumers

Populations of consumers are self-limited?

as they grow, their resources become scarcer

Consumers are limited by density dependent factors

Populations of resources are limited by consumers?

Resources tend NOT to be limited by density-dependent factors.

Predator-prey and carrying capacity?

In the presence of the predator, prey populations remained low

Predators can reduce prey below prey’s carrying capacity?

Predator-prey cycle?

Many predator and prey populations increase and decrease in regular cycles

1. Predators eat prey and reduce their numbers

2. Predators go hungry, and their numbers are reduced

3. With fewer predators, prey survive better and their numbers increase

4. With more prey, predator populations increase

Population cycles?

The synchrony of population cycles between consumers and the populations they consume suggests that these oscillations are the result of interactions between them.

What causes time delays in predator-prey interactions?

Predators have a slower life history

longer gestation

longer parental care

longer to sexual maturity

Lotka-Volterra model?

Simple mathematical model that reproduces cyclic predator-prey interactions

Lotka-Volterra model: Prey growth with predation?

aNpreyNpredator

Lotka-Volterra model: Predator growth with death?

Lotka-Volterra model: Prey population growth with predation?

Prey population growth (change in number of prey over time = instantaneous rate of change)

Per capita growth rate of prey (intrinsic growth rate)

Number of prey

Search efficiency of predator

Number of predators

Mortality due to predation

New parameter for prey population growth?

a

a?

search efficiency

– Also known as “attack rate”

– Probability of predators encountering and attacking prey

– If there was constant attack (extremely high search efficiency) this would be 1 (for every search there is attack)

If predators are limited only by prey, what would influence predator population growth?

New babies

Mortality

New babies?

How efficient predators are at finding prey, and converting it into baby predators?

Lotka-Volterra Model: Predator population growth with death?

Predator population growth (change in number of predators over time = instantaneous rate of change)

b?

Conversion rate (converts encounter rate to number of new predators produced)

– # of predators produced per prey item

– If one prey = one offspring, this would be 1

– If 6 prey = 1 offspring, this would be 1/6

Mortality rate of predators

r?

a * b * Nprey?

per capita growth rate of predators

Lotka-Volterra Assumptions?

• Closed system (one predator, one prey, no immigration)

• No refuges for prey

• No handling time for predators

• Prey grow exponentially in the absence of predators

• Predators consume infinite amounts of prey

Without consumers, what type of population growth would resources (i.e., prey) have?

– Assume resources have unlimited food, space, etc…

Exponential or geometric

Can consumers reduce resource populations below the resource’s K (carrying capacity)?

Yes

Herbivore and predator strategies put selective pressure on “prey”?

Prey have evolved numerous defenses to thwart predators and herbivores at each of these events.

Some of these are phenotypically plastic (occur only when predators are around)

Hunting?

a series of events, including detecting, chasing, and handling / consuming prey.

Nutritional defenses?

Predominantly in plants

Nutrients stored away from available parts of plants. Areas exposed to herbivores are not nutritionally dense.

Tolerance defenses?

Predominantly in plants

changes to plant growth in response to herbivory

• Rapid growth following browsing/grazing

• Rapid flowering and seeding following herbivory

• Increased investment in root and woody stem growth

Behavioral defenses?

Predominantly in animals

• Alarm calling

• Reduced activity

• Mobbing

• Schooling/flocking

• Growing/flowering when herbivores are scarce