levels of organisation and interactions

what is a population

a group of individuals of the same species

what are biological communities

assemblages of species populations - population of each species present in a specific area

what are communities usually classified by

plant components

why is this

Easy to recognise

Understand dynamics

Appropriate conservation

Can ID major biomes

draw a diagram that represents a niche (think cube on a graph)

what did tansley say was included in an ecosystem

self contained unit

biological community

abiotic environment

trophic levels

energy flow

biogeochemical cycles

what is the difference between interspecific and intraspecific

Intraspecific - within the same species

Interspecific - different species

give some examples of direct biological interactions

Physical contact

e.g. consumption of another individual (predation, herbivory, cannibalism), to mutual benefit (mutualism), & everything between

give some examples of indirect interactions

e.g. by shared resources, common enemies

how do we understand whether a biological interaction is benefiting or harming an individual

look at the effect on the fitness of each individual after the interactions

what are some considerations we should be aware of when using fitness as a measure of this

Level of benefit or harm is continuous, may vary

Interactions not always static - change as environment change

Levels are not discrete - there can be a big continuous range

give 6 interactions between species

mutualism, commensalism, competition, antagonism, amenalism, neutralism

what is mutualism and examples

both species benefit from the interaction

Cleaner fish, birds removing parasites, plant pollination and pollinators, nitrogen fixation by bacteria

what is commensalism

one species benefits, the other is unaffected

what is competition

both species are negatively affected

“Competition is an interaction between individuals brought about by a shared requirement for a resource in limited supply and leading to a reduction in the survivorship, growth and /or reproduction in the competing individuals concerned”

what is antagonism

one species benefits and one is disadvantaged

what is amensalism

one species disadvantaged, one benefits

whats neutralism

both individuals not affected by interaction

what is symbiosis

One or both species may be obligate (necessary)

i.e. cannot survive in the short or long term without the other species

what is endosymbiosis

symbiotes where one lies inside another

why is commensalism rare

close interaction of two organisms is unlikely to be completely neutral

E.g. epiphytes on plants may intercept  nutrients that otherwise would go to host plant; may shade host tree

E.g. Ramora on shark

give some other features of competition

Can be interspecific or intraspecific

Competitive interactions generally:

Need spatial and temporal co-occurrence

when does competition increase in intensity

as the

• Density

• Phylogenetic similarity

• Niche overlap

Of competing species increases

what are the 3 types of competition

Interference, exploitation and apparent

what is interferance competition

direct

Between individuals if interfere with other’s foraging, survival, reproduction

what is exploitation competition

indirect

e.g. use of resources depletes the amount available to others

explain apparent competition

Occurs indirectly between two species which are both preyed upon by the same predator

For example

• Species A and species B are both prey of predator C

• An increase in species A will cause the decrease of species B because the increase of A’s would increase the number of predator C’s which in turn will hunt more of species B

This can occur even if no direct interaction between A and B

what are the 2 competition outcomes

Contest

• Leads to regulation to carrying capacity

• Individuals compete for resource but one outcompetes the other and monopolises the resource

• The outcome is unequal asymmetrical

• Winners obtain all needs for survival and reproduction

• Losers get less than needed for reproduction and even survival

• So surviving individuals represent those that remain as a result of the population being regulated and the population being at the stable/steady level at or around the carrying capacity ‘K’

Scramble

• As population size increases all individuals have access to and acquire food resource

  All are affected in the same way

  Reaches a point where population gets very high and resources are very limited

  Leads to growth, reproduction and survival drop and population crashes

  Boom and bust where the carrying capacity is exceeded and then can drop below the potential K

  Populations can even go locally extinct in extreme examples

  So scramble competition occurs when all individuals in the population can acquire resource and all suffer the negative effects of competition

which outcome do we usually see for inteferance competition

contest

what outcome do we usually see for exploitation competition

scramble

features of a stable environment

K-selected organisms

Higher competitive ability

Contest outcomes

features of an unstable environment

disturbed and less predictable

r-selected organisms

Lower competitive ability

Scramble outcomes

what is a niche

n-dimensional hyper volume

reflects all the different facets of a species needs

can only carry a single species

what is the competition exclusion principle

competition between multiple species for a single niche can lead to exclusion

what is resource partitioning

differentiation of niches enabling species coexsistance

what is niche seperation or differentiation

resource partitioning over evolutionary time

can be over spacial or temporal scales

what is bottom up control

The amount of resource at the bottom of the food chain is determining population size

The more limited the resource, the more intense the competition

give some examples of antagonism

predation, parasitism, herbivory, cannibalism, etc.

what does predation influence

phenotypes over evolutionary time

diversity

distrubution

abundance

what is a trophic cascade

Abundance of what top predators eat and when can have ripple effects on population sizes of species in trophic levels below them

what is top down control

Where predation influences prey numbers

can top-down and bottom-up control happen at the same time in an ecosystem

yes,both bottom-up & top-down work together to drive changes in populations

give examples of how predation can be complex

Predator feeding on a competitively dominant prey species, reduces its numbers, and releases suppression of competitively inferior prey

Predator suppressing a competitive dominant species can be a good thing for species diversity

Predator feeding preferentially on competitively inferior prey species, reduces the number of species in community

why are predator prey graphs not usually smooth curves

A species is not necessarily cyclical throughout its range

Not all similar species in an area fluctuate cyclically

Different populations of a species may not cycle in phase

Larger amplitude than expected

Cycle not symmetrical

what extrinsic and intrinsic factors affect the fluctuation of lemming populations

Extrinsic factors

• Weather, food, predators, parasites

• Overcompensation and delayed density dependence

Intrinsic factors

• Hormonal change and behavioural change

• Aggressiveness varies throughout the cycle

• Dispersal rate depends on population density

what happens in early and late stages of lemming cycles

Early stage

• Plants abundant, high in nutrients with low toxins

• Populations increase rapidly

Later stages

• Increased dispersal, increased aggression, reduced lemming health, more disease transfer, higher predator abundance

• Heavily grazed plants respond and decline in quality (become toxic or unpalatable), lemming populations crash