Ecology/Evolution 3

Competition

any use or defense of a resource by one individual that reduces the availability of that resource to other individuals

intraspecific competition

members of the same species compete

interspecific competition

different species compete

Exploitative (resource) competition

populations depress each other by using up a shared resource

Interference competition

one population (or both) disrupts the ability of the other to exploit the resource base

Allelopathy

ex: plants secrete chemicals in the soil

Preemption

ex: barnacles grow first to prevent others from growing

Territoriality

ex: elf fights others to protect territory

The competitive exclusion principle

Conducted by Gause with paramecium species in simple environments with a single resource. Was found that the species affected the growth of each other. Two species requiring the same resources cannot coexist. The superior competitor will exclude the inferior species

Niche

represents the range of conditions and resource qualities within which an individual or species can survive and reproduce. multidimensional.

overlap of these of two species determines how strongly the two species might compete with each other.

4 dimensional niche

1) What you eat

2) Where you nest

3) Type of forest

4) When you hunt

Fundamental niche

the total range of resources a species can use under ideal conditions

Realized niche

the resources a species actually uses within the community

Resource partitioning

reduces competition to a level that allows coexisting

Symbiotic relationships

any prolonged close relationship between different species

Competition symbiosis

neither species are benefitted

Amensalism

one species is harmed while the other is neutral

Exploitation

one species benefits while the other does not.

Commensalism

one species benefits while the other is neutral

Mutualism

both species are benefitted

Exploitation includes

1) Predation: predator vs prey

2) Parasitism: pulling resources from a host

3) parasitoidism: internal predator

4) herbivory: eating vegitative material

Plant defenses against predation

1) Chemical: produce noxious chemicals

2) Mechanical: develop structures that make it hard to be eaten

3) Nutritional: growing structures that are less nutritious

4) Tolerance: adaptations to regrow

Parasitoids

internal parasites that will virtually always kill their hosts. Consume their prey from the inside

Animal defenses against predation

1) Chemical: produce noxious chemicals

2) Physical: develop physical barriers (shells)

3) Aposematism: warning colors and sounds

4) Crypsis: camouflage

5) Mimicry: mimicking species to avoid

6) Behavioral: minimizing risk with behavior

Reasons why exploitation is interesting

1) Coevolution

2) Population cycles

Why sex?

sexual reproduction results in greater genetic diversity. greater genetic diversity increases resistance to parasites

Community

a group of species interacting directly or indirectly. linked by space and time. May be composed of several different guilds

Guild

a group of organisms interacting directly or indirectly that exploit a common resource

Communities are determined by several factors

1) Diversity and abundance of the species within them

2) Stability

Comparative community ecology begins with diversity which is a combination of two measurements

1) Richness

2) Evenness

Richness

the number of species present

Evenness

the relative abundance of present species. A measure of the spread or proportion of individuals of these species

Simpson's D index

A quantitative assessment of richness and evenness comes in the form of diversity indexes.

D= the sum of the number of individual species (i) divided by the total number of individuals of all species) squared

1/D

has the advantage of being somewhat more "intuitive" because it represents the "average" number of species you'd expect to encounter in that community.

How are populations dynamic

the number of individuals change over time

How are communities dynamic

the species change over time

Succession

the sequence of changes initiated by disturbance

Primary succession

succession on virgin substrates (glacier movement)

low tolerance for shade, high seed number, small seed size, low root:shoot, small mature size, short lifespan

Secondary succession

succession on non-virgin substrates (prairie burning)

high tolerance for shade, low seed number, large seed size, high root:shoot, large mature size, long lifespan

Low root to shoot ratio

lots of stem. sacrifices nutrient/water acquisition and capitalizes on fast growth to beat competitors for sun

High root to shoot ratio

less stem. maximize nutrient/water acquisition and sacrifices rapid growth

Pioneer species

colonizers that change the environment. environmental changes may favor later successional species at the expense of these

Intermediate disturbance hypothesis

a little bit of disturbance is a good thing for community diversity. Not too much that the more stable long-term species can't establish but just enough that superior competitors can not dominate the community.

Those interested in community stability are interested in

1)How big of a change in the community did the disturbance cause?

2) How quickly did the community recover from the disturbance? 3) How closely did the post-recovery community resemble the pre-disturbance community?

Resistance

how much a community changes due to a particular disturbance

Return/Recovery time

how long it takes a community to return to a stable state after being disturbed. Man made events result in a longer time. (includes war, but meteor strikes result in the longest recovery time)

Resilience

how close the post-recovery community resembles the pre-disturbance community. Communities with low resilience can return to an alternative stable state.

Why are some communities more stable than others?

1) bio diversity

2) complexity or species connectance

Why might biodiversity matter?

1) More niches are filled in diverse communities

2) If conditions change (i.e. drought), there is a greater chance there will be species whose niches include the new conditions

Connectance

the number of actual links between species divided by the number of species squared.

A high level of species connectance may lead to community stability.

Can remove more species from communities with high connectance than those with low connectance without causing additional species to go extinct.

Dominant species

very important, but this is because they are so abundant (ex: trees)

Keystone species

very important, but due to what they do more than how many there are

Keystone modifiers/ecosystem engineers

determine the prevalence and activities of many other species by dramatically altering the environment (ex: beavers)

Trophic structure

a food chain that shows some of the relationships in communities. Goes from bottom with energy flow.

primary producer-primary consumer-secondary-consumer

Trophic cascade

shows the direct, negative, and indirect, positive effects of a trophic structure

Food webs

made of multiple, often intertwined food chains. essentially a "who ate whom" within the community

Gross primary productivity

total rate of energy captured by autotrophs. Some absorbed energy is re-radiated as heat; the rest powers this. The plant consumes some of this to produce energy during respiration. this energy is lost as heat.

Net primary production

the difference between the GPP and respiration. the rate at which plant stores energy as biomass (available for plant growth and reproduction).

Terrestrial systems limitations

limited by water and temperature

Aquatic systems limitations

limited by nutrients

Water cycle

1) water evaporates

2) warm, moist air rises up the mountains

3) water vapor cools and condenses to form clouds

4) precipitation falls on the windward side of the mountain

5) air mass is now dry with no water vapor

6) dry air falls and a desert forms

Secondary productivity

primary production fuels secondary production.

1) energy ingested by a heterotroph can be assimilated or lost as waste (egested)

2) Energy assimilated is either used for maintenance (respiration, including heat) or production (growth, storage, reproduction)

Consumption efficiency

how much out there is consumed.

The ingestion divided by the production

Assimilation efficiency

how much of that consumed is assimilated (not lost as waste)

Assimilation divided by ingestion

Production efficiency

how much of that assimilated is used to make more consumers (and not lost to respiration/heat)

production divided by assimilation)

Trophic efficiency

how much of the total out there ends up as new consumers

production of sheep divided by production of plants

Greenworld hypothesis

the world is green because herbivores keep consumers in check. All species have the same impact on the system they're in. some species are more equal than others.