Ecological community Flashcards
Ecological communities
A community is a group of potentially interacting species that occur together in space and time
bioregions
- communities can be defined by plants occurring there/ The endemic species of each area are low but different in relative abundance and dominat is the main driver.
key processes in ecological communities
-Selection = changes in community structure caused by non-random(“deterministic”) fitness differences between taxa
Selection pressure:
• Varies over space / time
• Constant
• Density-dependent
-Drift is random changes in the relative abundances of different taxa within the community through time“Neutral processes”
-Diversification is the evolution of new lineages (including new genotypes, forms, varieties, sub-species and species) from existing lineages
-Dispersal is the movement of individuals from one place to another, as propagules (seeds and spores), larvae, juveniles or adults
• Immigrating \ emigrating
• Source \ receiver
• One-way (large to small)
• Linking local communities
explain the current diversity of Australian plant communities
Persistence of rainforest species that evolved prior to the breakup of Gondwana.
Persistence of species that evolved after the breakup of Gondwana in response to a trend of drying of the continent and increased frequency of fire.
Dispersal of rainforest species from SE Asia into Australia.
different form of diversity
⍺ diversity : the composition of a local ecological community with respect to its richness (number of species), evenness (distribution of abundances of the species), or both
ß diversity : the extent of change in community composition, or degree of community differentiation, across a region.
Shannon index
S = total number species Pi = proportion for i th species H = Shannon diversity index Hmax = maximum possible H if individuals completely evenly distributed among species H= -(Sum of Pi x lnPi) Equality= J= H/lnS
Simpson’s index
S = total number species Pi = proportion for i th species D = Simpson’s index 1-(Sum of P square)
Problem with measuring diversity
- detectability of species ( some species are hard to detect the present) and even if detection is possible. The richness is unknown. or it’s only possible to measure the possibility of the present. in that case, the sum of the probability is the species richness
- Taxon, many species are still unknown so hard to determine species present
G.E.Hutchinson fundamental niche
Niche of a species is a multidimensional hyperspace, containing conditions and resources that allow the species to survive
- condition are aspect of the environment that are not affected by consumtion
- resources are aspect of the environment that become less abundant as it is being consume
Realised niche
the actual niche that a species are found in is smaller - reasons include: • Competition • Dispersal limitations • Disturbances • Stochasticity
Environmental gradients
- Variation in the condition and resources of the environment • Cover • Aspect • Solar radiation • Temperature
Environmental variables
Terrestrial Climate: annual precipitation, minimum temperature of coldest period;
temperature seasonality, potential evapotranspiration; humidity or vapour
pressure deficit; solar radiation adjusted for topography; snow cover; frostfree days; topographic: slope roughness (variation); soil: type, depth, water
holding capacity
Freshwater Variables characterising upstream (catchment), local watershed, riparian
zone and downstream conditions, including flow magnitude and variability,
frequency of flood and drought events, temperature, water quality (N, P),
streambed conditions (bedrock type, surface complexity, substrate particle
size)
Marine Depth, seabed topographic features, temperature, salinity, dissolved
oxygen, currents, productivity (e.g. chlorophyll-a)
How are communites shaped based on their interaction
- Competitive exclusion
- Resource partitioning
Spatial and temporal variability allows co-existence
Competitive exclusion
If two species compete for the same limited resource, one will dominate in the long term
the growth of two species of Paramecium when cultured separately and together. The P.aurelia out compete the P.caudatum
Resource partitioning
-species change morphology (size and shape) to reduce competition = character displacement
Mud snails, Hydrobia, two species change size when they are in a same community even though they have similar when they are separates
-species change behaviour
golden spiny mouse and common spiny mouse, both are nocturnal but when together , golden become diurnal
Measuring community patterns in space
Objective methods
Based on data
Pattern analysis
• association (how similar they are via cluster analysis and bray-curtis similar scale)
• classification (examining the composition of species at sites. those that have the same species are pooled together into a class. then, predict the effect of present or absence of those species in the comunity
• ordination (difference in condition and resources)
Mapping a distibution of species
- look at a community in regard to their environment
-define a community that occur in an area
-model base on measurement
-map it out the community to their enviroment
Two steps: classify the organism there, then predict the map
interspecific interactions
Community interactions are classified by whether they help, harm, or have no effect on the species involved \+/+ mutualism \+/0 comenialism -/- competition \+/- paratism or predatism
Parasites
- Smaller than host
- Live on or in host for extended time
- Usually don’t kill host
- Host may recover from parasite
- The habitats of parasites are themselves alive
- Grow
- Respond
- Evolve
- Move
Abundant of parasites
• Protozoans • Animals • Fungi • Plants Relative abundance of different taxa, and proportion of parasitic species in those taxa Host species > 1 parasite the total biomass of parasites often equalling or exceeding the biomass of some tropic levels.
Predation
Feeding of one organism on another
• Predators
• Animals that capture and eat other animals
• Herbivores
• Animals that consume plants / plant parts
Keystone predator
A keystone predator has such an important role in the community that it helps to define the community. If it is removed, the community will be drastically different, or cease to exist
Indirect effects of predation
- Developmental, morphological, physiological, behavioural
- Significant costs
- Meta-analysis = systematic analysis of results of published research
- clear evidence that the impact of intimidation on prey demographics was at least as strong as direct consumption
example of Indirect effects of predation
Nursery web sipder
• Forest in Connecticut, USA
• Hiding: 18% reduction in daily activity
time
• Change of diet: 70% grass if no spider;
42% grass if spider
Impact spatial arrangements
- Finland forest bird community
- Sparrowhawk (predator)
- Predation risk closest to nest
- Birds of preferred prey size avoided nests
Herbivory & Australian vegetation
Native herbivores: • wombat, kangaroos, bettongs, possums… • grasshoppers, beetles, termites.. Introduced: • Cattle, goats, camels, deer, rabbits.. Change composition and structure Increase cover Increase exotic weeds Decrease plant species richess
Structure classification
