community ecology & functional roles Flashcards
ecological community
- all pops of all species living close enough for actual (or potential) interaction
- includes direct & indirect interactions
direct and indirect interaction example
direct: catapillar grazing on leaf
indirect: effect of catapillar parasites on plant
5 interaction examples
- Competition
- Predation
- Herbivory
- Parasitism
- Mutualism -> both species are mutually benefited
interspecific competition
2 or more species competing for the same limited resource
keystone species
- not most abundant species
- helps define ecosystem
-> without species: ecosystem would be dramatically diff / cease to exist!! - eg. sea otters
functional groups of communities examples?
- canopy community
- grazer community
- decomposer community
- tree community
sp interactions
- help
- no effect
- hinder
interspecific interactions
interactions between species in a community
interspecific competition
2+ sp competing for same limited resource
- resource limits survival & reproduction of both individs
- competition has a -ve impact on both/all interacting sp
What happens in community when 2 species compete for limited resources?
include example
competitive exclusion
-> strong competition can lead to exclusion of a sp (Gause 1934)
example: lab experiments on 2 protozoa species:
- Grown independently both sp thrive
-> rapidly increase then level off at carrying capacity - Grown together, 1 sp driven to extinction
-> inference: 1 sp had a competitive edge in obtaining food
-> CONCLUSION: 2 sp who compete for same limiting resources cannot coexist permanently in same place
ecological niches
(the type of niches possible)
set of biotic & abiotic resources that a sp uses in its env
- tolerances e.g. temp, salinity
- habitat e.g. substrate on which it grows, timing of active
- resource requirements e.g. type & size of prey it eats
suggest how so many species can co-exist despite competition?
(use niches)
sp can co-exist if…
-
suff diff in niche requirements
OR - if their niches can change
fundamental niche
niche sp could potentially occupy
realised niche
niche sp actually occupies
7 sp of Anolis lizards all live in the same area and all feed on insects and other small arthropods.
How do they all survive?
niches are differentiated
-> competition is ↓ as they all have diff perches
suggest 2 ways niches can be partitioned
- space
- time
example of niches partitioned in time
common spiny mouse (nocturnal) & golden spiny mouse (diurnal) co-exist
- ‘golden’ is naturally nocturnal -> changes biological clock to be diurnal when ‘common’ present
- this behaviour change suggests sp were competing & partitioned niches to co-exist
how can 2 closely related sp occur?
- allopatry -> geographically separate
^pops are morphologically similar & use similar resources
- sympatry -> geographically overlapping
^pops show diffs in morphology & resource use – would otherwise potentially compete
character displacement
(indirect evidence of effects of competition)
- tendency for characteristics to diverge more in sympatric (same env) than allopatric pops. of 2 sp
aka…
- change that occurs when 2 similar sp inhabit same env
adaptations of predators
-
sensory apparatus
-> forward-facing eyes
-> heightened visual & auditory acuity
-> heat sensing organs -
catching, killing, subduing prey
-> claws
-> teeth / fangs / beaks
-> stings
-> poisons
-> behaviours
-> webs / traps
adaptations of prey
-
behavioural adaptations
-> fleeing
-> group living
-> self / group defense
-> hiding -
morphological / physiological adaptations
-> swift & agile
-> horns & spines
-> noxious secretions
-> bright colours
-> autotomy (self-amputation)
colour adaptations
- crypsis colouration -> makes prey difficult to see
- aposematic (warning) colouration -> predators avoid bright colours
Batesian Mimicry
palatable / harmless sp mimics unpalatable / dangerous sp
e.g. caterpillar mimicking a snake
evolves via natural selection…
- individs in harmless sp that happen to more closely resemble harmful sp are avoided by predators that have learned to avoid harmful ones
- closer resemblance evolves via this selection pressure
Müllerian Mimicry
2+ unpalatable sp mimic each other
eg. Heliconid Butterflies & Poisonous (Cyanide) Aposematism
- shares cost of predation as predators learn avoidance…
- the more unpalatable prey there are, the faster predators learn to avoid prey with that appearance
- mimic each other’s honest warning signals, to their mutual benefit
dom species
- most abundant / have highest biomass in a community
- exert strong ecological effect as result of being highly abundant
-> e.g. impacting light levels, nutrient levels and water availability to other sp
What causes a species to become dominant within a community?
2 main hypotheses:
- dom sp are more competitive at obtaining resources
- dom sp are better at avoiding predation / disease
invasive / alien sp example
Signal crayfish
- In Europe, crayfish plague (caused by water mould Aphanomyces astaci) was damaging European crayfish stocks
- Signal crayfish were imported from
N America->Europe to allow recreational & commercial crayfish capture - Signal crayfish: unknown carrier of crayfish plague, but suffers low mortality from pathogen
- to European sp: infection is fatal
- Signal crayfish acted as disease reservoir from which European sp were infected – is now a problematic invasive
We can measure the impacts a dom sp has on a community if it is removed.
example?
American chestnut -> dom sp in N. American deciduous forests up to 1910 (>40% of mature trees)
- chestnut blight: fungal infection introduced into US via imported timber from Asia
-> 1950 ~ all American chestnut trees gone
mixed effect on other species…
- Oak, Hickory Beech & Red Maple ↑ abundance
- mammals & birds unaffected
- 7/56 moth & butterfly sp that fed on American chestnut became extinct
How to research species removal?
- natural experiments (e.g. Zostera)
- humans removing dom. sp e.g. clearing land for agriculture
- mathematical modelling
- microcosm experiments
evidence of sea otters being a keystone species
In Alaska, sea otters are predator of sea urchins
- sea urchins eat kelp roots
- where sea otters abundant: kelp forests abundant
- where sea otters less abundant: kelp is v rare
BUT… Orca predation becoming ↑ common on Sea Otters…
- ↓in Harbour Seal & Steller’s sea lion (Orcas typical prey) -> sea otter pop ↓
- sea urchin pop ↑
- loss of kelp forest?
foundation sp / ecosystem engineers
animals that physically alter their env rather than via trophic interactions
eg. beavers…
- fell trees & create dams
- clearing forest & creating large areas of flooded wetlands
Beavers can have a cyclic effect on rivers and streams.
explain this
foundationn sp
- abandoned Beaver ponds “silt up”
- eventually dams breach leaving wetland habitat
- Riparian tree sp re-colonise & beavers return
knowledge of top-down and bottom-up control enables us to solve ecological problems.
what ecological problems?
- many freshwater lakes in/near industrial / urban areas suffer from pollution (sewage & fertilizer run off)
^result in poor water quality
- ↑ nutrient levels => growth of algae and cyanobacteria (harmful algal blooms)
Knowledge of Top-Down and Bottom-Up control enables us to solve ecological problems.
case study?
Lake Vesijärvi in Finland
- highly polluted from industrial & household waste
- in 1976, industrial regulation stopped pollution entering lake
- water quality started to ↑ BUT later huge blooms of cyanobacteria (blue- green algae) began
MORE INFO IN BOOK NOTES
biomanipulation
- adding / removing sp from ecosystem…
- to achieve a +ve change in env
