Community and environmental management

Question 1

what are communities?

Answer 1

> An interacting group of various species, in a common location
communities are more than just a collection of interacting species
community processes can be multiplicative - more than the sum of their parts
not random

Question 2

what are the different types of interspecies interactions?

Answer 2

>competition  -/-
> predation +/-
  -animals : predators (+), prey (-)
  - herbivory: herbivores (+), plants (-)
>parasitism and disease +/-
> mutualism +/+
  - pollination
> commensalisms 0/+

Question 3

what are the important questions in need of consideration when looking at the emergent properties of communities?

Answer 3

1) why do higher diversity communities have higher productivity?
2) why are higher diversity communities more resilient to disturbance?
3) why are higher diversity communities more resistant to invasion?
4) what are reinforcing effects?
5) how do individual species affect community dynamics?

Question 4

1) why do higher diversity communities have higher productivity?

Answer 4

> higher number of niches filled
meaning that resources that might not have been used are now being used
interspecies relationships
INTRA -species interactions
less competition of individuals of each species
Slight differences in resource utilisation leads to less competition
Intraspecific competition should be stringer than interspecific competition
when found in same area - more species = more resource utilisation

Question 5

what is the implication of competition differential? i.e., why does arrangement of species matter?

Answer 5

> if intraspecific competition is stronger than interspecific competition then the way species are arranged will affect productivity.
i.e., many of the same species grouped together is not productive, as more intraspecific competition.
the most beneficial arrangement is to have a random mix of all species
- evens out species going for different nutrients

Question 6

how is the idea of arrangement important when thinking about agriculture?

Answer 6

> commercial crops are typically planted in monoculture,

> yields could be higher is multispecies are planted.

Question 7

2) why are higher diversity communities more resilient to disturbance?

Answer 7

> higher diversity means that greater number of species performing the same function
able to fill the void if one becomes extinct due to a disturbance.
low diversity means that if one species goes extinct, the function it performs could also stop happening is there isn’t another organism to take its place.
this is called functional redundancy.

Question 8

3) why are higher diversity communities more resistant to invasion?

Answer 8

> high diversity communities are harder to invade than low diversity communities
lower number of niches available in highly diverse communities
think of the seat analogy.

Question 9

How stable are communities?

Answer 9

> through resilience and reinforcing effects.

> resilience is a community property

Question 10

what are reinforcing effects?

Answer 10

> resident communities maintain environmental conditions that discourage the formation of new communities
ecosystem engineers

Question 11

what is an ecosystem engineer?

Answer 11

an elephant for example.
> an organism that changes the landscape of a communities environment.
> elephants converts dense woodland to grasslands
> grasslands burn more readily, further favouring grasslands
> grasslands support more ungulates (i.e., elephants, zebra, grassing animals)
Other examples include:
> fire promoting species
> shade tolerant species

Question 12

5) how do individual species affect community dynamics?

Answer 12

> most species are rare
keystone species and dominant species
- keystones have a large impact disproportional to their biomass
- dominants have impacts that are proportional to their biomass
example of keystone = wolves in yellow stone
predators are often keystones, as they promote mutualism.
just because one species is disproportionally important, it DOES NOT means that other species combined are not equally important.

Question 13

what are ants an example of?

Answer 13

ecosystem engineers as well as keystone species
> nutrient recycling
> create large structures

Question 14

how are indigenous people ecosystem managers?

Answer 14

> a study in 2008 monitored foraging and land use of Martu people
remote part of Australian Western Desert
hunters burn spinifex
correlated foraging (burning) activities with habitat diversity
aboriginal fires differed from lighting fires
smaller patches with more diverse vegetation
more diverse patches meant higher productivity
burning little patches every now and then creates a heterogeneous area, more diversity of plant species
NOT burning for long periods of time homogenises the land and leads to uncontrollable fires.

Question 15

how will the adoption of aboriginal fire regimes benefit the environment?

Answer 15

> enhance conservation practises
Avoid devastating hot fires
early season burnings by aboriginal rangers is expected to reduce greenhouse gas emissions by 100,000 tonnes per year

Question 16

why does fire promote higher diversity?

Answer 16

> adaptations of species
- nutrient releases
intermediate disturbance
different successional stages of plants.

Question 17

what is the intermediate disturbance hypothesis?

Answer 17

> highest species diversity associated with intermediate levels of disturbance.
kind of like a bell curve, not enough disturbance = homogenisation, too much disturbance = homogenisation (as only certain species can recover quickly enough)
intermediate disturbance = highest species richness.

Question 18

what is disturbance and succesion?

Answer 18

> a change to the environment (fire, storm, tidal wave etc)
succession = the successive turnover of species following disturbance.
early and late succession

Question 19

what are early successional species?

Answer 19

opportunistic
> lots of seeds
> grow faster
> more energy into leaves
> wind or animal (external) dispersal
> better suited to large scale frequent disturbances

Question 20

What are late successional species?

Answer 20

Equilibrial
> fewer, larger seeds
> grow slower 
> more energy into stems and roots
> gravity or animal (internal) dispersal
> better suited to no disturbances.

Question 21

how do intermediate disturbances increase the diversity of organisms? ( in terms of early and late successional species)

Answer 21

> no disturbance = more late successional species
lots of disturbance = more early successional species
therefore intermediate disturbances are a mixture of both of these types of organisms to flourish, therefore, a higher diversity of organisms exist.

Question 22

define net primary productivity

Answer 22

net primary productivity of an ecosystem is equal to the gross primary productivity minus the energy used by the primary producers for respiration.

Question 23

what are the two food chain theories?

Answer 23

> dynamic stability hypothesis

> energetic hypothesis

Question 24

what is the dynamic stability hypothesis?

Answer 24

> population fluctuations at lower trophic levels due to disturbance are magnified at higher levels.
the longer the chain the harder it is for the top predators to recover from the disturbances.
predicts that longer chains will be found in more stable environments

Question 25

what is the energetic hypothesis?

Answer 25

> the length of the food chain is limited by the inefficiency of energy transfer along the chain
only 10% of energy consumed is transferred along the food chain.
predicts that food chains will be longer in more productive system
90% of energy is lost.
in terms of biomass, food chains can’t have a greater biomass as you go up the trophic levels.

Question 26

what are trophic controls on communities?

Answer 26

> bottom-up control
top-down control
can change with conditions in the community