C.1 Species and Communities Flashcards
Factors affecting animal distribution
Territory Food Water Competitors Parasites Human influences Predators Temperature Day length Breeding sites
Factors affecting plant distribution
Parent material Soil salinity/pH/minerals: Mg, K, Cl, P, N, S Light intensity Day length Temperature Rainfall Human influences Competitors
Uses of quadrating
Measuring population size/density/percentage coverage/biodiversity
- Compare populations of different species in the same area
- Compare populations of the same species in different areas (along a line transect)
Consistency in quadrating
Decide which borders are “in” and “out”. Individuals on the “out” border should not be counted, whereas those on the “in” border should be counted.
How to count in quadrating?
Count plants only if they are attached to the soil within the quadrat (flat-laying foliage may need to be lifted out of the way to see roots)
For abundant populations (e.g. grass), percentage cover should be counted instead.
Estimates of uncertainty should be included (e.g. plus or minus one)
Data should then be processed and tested for significance (chi-squared).
Transect
Line transects can be used to correlate the distribution of a species over a set distance with an abiotic variable (e.g. human disturbance, light intensity).
Quadrats can then be placed at regular intervals along the transect. The data can be presented in a kite diagram (where the verticle distance equal the size of population).
Shelford’s law of tolerance
Graph of population size (number of individuals) against a biotic/abiotic factor (from low to high).
Shows the zones of intolerance, limits of tolerance, zones of stress, and optimum range
Limitations of Shelford’s law of tolerance
- Symmertric graph in real life the graph may not be necessarily symmetrical, as sometimes scarcity may impose a more accute effect on the population size than abundance or vice versa (upper limit of tolerance for toxin, but no lower limit)
- Different individuals of a popultion have different tolerance to the same factor –> difficult to quantify the limits
Interspecific interactions
Competition Parasitism Herbivory Predation Mutalism Commensalism
Competition
Where two species acquire similar niches (require the same resource) and consumption by one species reduces the availability of the resource to the other species.
Ex: bluebells and bracken competing for light –> bluebells minimized competition by adapting to growth earlier than taller-growing bracken.
Parasitism
When one organsim (parasite) feeds off another but does not normally kill it. In this situation the host is harmed whereas the parasite is benefited.
Ex: tapeworms in human
Herbivory
Primary consumers feeding on producers.
Ex: cane beetle feeding on sugar cane
Predation
A consumer feeding on another consumer.
Ex: dingo in New South Wales feeding on red kangaroo
Mutualism
Two species live closely and mutually benefit from their interactions.
Ex: zooxanthellae and reef-building corals
Commensalism
Two organsims interact, with one benefiting from the interaction while the other is neither harmed nor benefited.
Ex: The Hawkfish living in fire corals, gaining protection from the coral.
Zooxanthellae and corals
Zooxanthellae are benefited:
Support and protection from Calcium Carbonate skeleton from coral
Nutritions for photosythethesis (CO2)
Corals are benefited:
Products of photosythesis: glucose, O2
Zooxantehllae helps corals to remove wastes (CO2)
Keystone species
Species that have a more than proportionate effect on the structure of an ecological community. The presence of keystone species prevents species from monopolising critical resources.
Ex: sea otters feeding on sea urchins, controlling their numbers, so that kelp and other plant species would not be over-consumed by urchins –> maintains kelp forests as a habitat for other species.
Outline the effects of removing the seastar Pisaster from the community
Biodiveristy reduced rapidly from 15 to 8 in just one year, because the remaining species immediately compete with each other to occupy the newly available space and resources.
Within 3 months, Balanus glandula had become dominant in the area.
9 months later, B. glandula was replaced by another barnacle Mitella and the mussel Mytilus. The population size of Mytilus increases because it was consumed by Pisaster before its removal.
The succession continues until Mytilus becomes the dominant species –> wiped out populations of benthic algae.
Some species of limpets emigrated to other habitats due to lack of food/space.
In whose experiment is Pisaster removed?
Robert Paine’s
Niche
The unique ecological roles fulfilled by each species in an ecosystem, including its spatial habitat, its interactions wih other species, and its impacts on the ecosystem.
Fundamental niche
The full range of environmental conditions under which a species can potentially survive and reproduce.
Realized niche
The specific set of environmental conditions udner which a species can actually survive and reproduced, taking the biotic limiting factors into consideration.
Smaller than the foundamental niche.
Gause’s experiment
Cultured two species of paramecium separately and in a mixed population.
P. aurelia and P. caudatum
When grown separately, each population grew to a high maximum, showing its foundamental niche.
When grown together in a mixed population, interspecific competition occurs: one species would dominate (P. aurelia), causing the other to declien/extirpate.
The competitive exclusive principle states…
Species with identical ecological niches cannot survive in the same area indefinitely.
Result:
1. One dominates, the other decline/extirpates
2. Both narrow their niches to avoid competition (e.g. bluebells begining growth earlier than bracken, avoiding competition for light).
