APS123 Thomas Flashcards
A community consists of…
all of the individuals of all of the species that inhabit a particular area
Species richness within sites =
a - diversity
alpha
Species richness in all sites =
y - diversity
gamma
B - diversity (beta) measures…
how different the samples are across the sites, or the turnover of species
What is the Jaccard coefficient used for?
To compare the community composition of 2 sites
What is the equation for the Jaccard coefficient?
a/a+b+c
a = number of species found in both sites (not total) b = number of species found in site 1 but not site 2 c = number of species found in site 2 but not site 1
When communities are identical, the Jaccard coefficient =
1
When communities are completely different, the Jaccard coefficient =
0
Communities are often …
nested
(smaller community occurs in a larger community, which may occur within an even larger community etc.)
- but communities can also not be nested (no species in common)
What does SARs stand for?
Species area relationships
You expect … islands to have more species, as they contain more …
larger, niches
SARs are …-…
non-linear (due to limitations e.g. of potential niches)
S =
cA^z
S = number of species A = area c = intercept z = exponent
If you take a log of both axes when plotting number of species against area of island, you get a …
straight line relationship
y =
c + mx
SARs are useful when thinking about habitat….
fragmentation (e.g. in forestry and logging)
The slope of SARs is remarkably …
consistent (order of 0.25-0.3)
- typically equates to doubling of richness with tenfold increase in area
Intercept is highly …
variable
- we require this information (as well as the slope) to calculate species richness
Mountain peaks create “…” of habitats
islands
Highest elevation montane habitats of…
mixed coniferous forest
Mid altitudes of…
pinion-juniper woodland
Alpha diversity was surveyed in pinion-juniper woodland…
on different isolated mountain tops
What relationship was found between number of species and area in pinion-juniper mountain woodland?
Clear positive relationship as expected
There is a predicted … shift in habitat types with a 3 degree increase in temperature
altitudinal - p-j woodland pushed up and restricted to mountain tops (therefore reduction in habitat area)
- decrease in diversity assumes inability to disperse to other mountain tops and migrate
Rare species tend to occur…… and are predicted as more likely to … …
where species richness is high (there are lots of other species), go extinct
Mainland SARs tend to have…
shallower slopes than island SARs
Why do islands have fewer species than mainland areas of equivalent size?
Saturation decreases further away from mainland, smaller proportion of species shared with mainland
Saturation by isolation suggests that…
area (and by extension habitat diversity) is not the only, or even main, factor driving alpha diversity in island-like systems
Many systems display Species Isolation relationships -
alpha diversity declines with isolation from the mainland
Who put forward the Island Biogeography theory?
MacArthur and Wilson (1963)
- thought that the habitat-area relationship was incomplete - developed a model predicting species richness on islands
How are island communities formed?
- Species must arrive on an island (immigration)
- Species must persist on an island (extinction)
- Species richness is a balance of immigration and extinction
As immigration rate to an island increases,
species richness decreases
- consider island with no species - most colonising individuals will be from unrepresented species
- consider island with many species - most colonising individuals will be from species already present on the island
As number of resident species increases,
extinction rate increases
- increased competition suppresses population sizes so species extinction rates increase
In 1883…
a catastrophic volcanic explosion devastated the island of krakatoa - its flora and fauna were completely exterminated
Number of species on an island reaches…
equilibrium
- dynamic - species change, but number of species remains more or less constant
Macroecology focuses…
over wide spatial and temporal scales
- SARs, island biogeography and latitudinal gradients are examples of macroecology
Who first discussed the latitudinal diversity gradient?
Alexander von Humboldt
Von Humboldt broadly suggested that biodiversity was higher at..
lower latitudes (nearer tropics)
Understanding global distribution of species focuses on predicting causative factors that drive variation in rates of immigration, extinction, emigration and speciation. There are 100s of hypotheses but two main categories:
- climatic/environmental factors (ecology)
2. Historical factors (evolution)
The environment filters the species that can occur in a given area and may determine upper limits on species richness. A couple of these environmental filters are to do with…
- energy/ productivity
2. spacial and habitat hetergeneity
PET is
potential evapotranspiration
- amount of water that would evaporate or be transpired from a saturated surface - crude measure of available energy or productivity
In general, as energy availability increases,
species richness increases
- for ectotherms, extra atmospheric warmth enhances intake and se of food resources
- for endotherms, extra warmth means less use of resources to maintain body temperature and more available for growth and reproduction
- not always clear positive correlation, sometimes u-shaped, negative, no correlation etc.
Habitat heterogeneity often is positively correlated to..
species richness
Climate and environment determine..
the number of species that can co-exist, and govern the movement of species into and out of an area (immigration and emigration)
What are the 3 hypothesised processes for historical determination of diversity?
- Tropical cradles of diversity - tropics home to young, rapidly speciating lineages (speciation rate peaks in the tropics + extinction rate invariant with latitude)
- tropical museums of diversity - tropics are home to old, relictual species (speciation rate invariant, extinction rate declines in the tropics)
- Out of the tropics - species form in the tropics and move to extratropics (speciation rate peaks in the tropics and extinction rate declines in the tropics)
What are the 3 hypothesised processes for historical determination of diversity?
- Tropical cradles of diversity - tropics home to young, rapidly speciating lineages (speciation rate peaks in the tropics + extinction rate invariant with latitude)
- tropical museums of diversity - tropics are home to old, relictual species (speciation rate invariant, extinction rate declines in the tropics)
- Out of the tropics - species form in the tropics and move to extratropics (speciation rate peaks in the tropics AND extinction rate declines in the tropics)
Speciation rate =
Extinction rate =
Net diversification =
birth rate
death rate
speciation rate - extinction rate
In reality, speciation rates are … in the tropics, and extinction rates are … in the tropics, and transitions … the tropics are much more frequent than transitions … the tropics - consistent with…
higher, lower,
out of, into,
the out of the tropics model
In marine fish, speciation rates are higher…
outside of the tropics
- don’t know, but extinction rates may be particularly low in tropics
Evolutionary history at the … level determines … … … (e.g. tropics vs temperate
regional, gross diversity patterns
Processes of speciation and extinction govern…
species available to form local communities
What are ecogeographical rules?
variation in the traits of organisms over geographical or environmental gradients
e.g. bergmann’s rule describes changes in body size with latitude/ temperature
Bergmann observed that…
body size increases with HIGH latitudes in mammals
- suggested advantageous as reduces heat loss from lower SA:V ratio
- observation based on latitude but proposed mechanism based on temperature gradient
In birds, higher species richness with
lower body mass
What is Allen’s rule?
Length of appendages in closely related vertebrates increases in hotter environments
e.g. fennec fox vs red fox vs arctic fox
Bird’s bills are a major source of…
heat loss
Bill size declines with…
latitude and altitude
- consistent relationships within multiple bird families
- data support both pattern and process
For the example, several small reserves accumulate..
species faster than 1 large island of equivalent area]
- even though the data are nested they are not perfectly nested
- if species are complementary
… of global land surface is in protected areas
- 5%
- but many (20% of) protected species receive no protection at all - worst for amphibians
Typically, protected areas have been set up…
opportunistically - often on land nobody else wanted
Unfortunately, people and biodiversity often like the same places (low …, highly productive …) - and existing reserves are not effectively positioned to protect biodiversity
elevation, soils
When deciding which areas to protect, choosing sites based only on local species richness (a-diversity) ignores…
the important role of community dissimilarity (B-diversity) - instead we should pick the sites that would protect complementary sets of species
Random is better than using..
hotspots
apart from threatened species
Complementary sites much better than
random and hotspots
Hotspots don’t take … into consideration
turnover
It is argued that minimising edge-area ration in reserve design is desirable to…
protect as much core habitat as possible given onging habitat fragmentation
SLOSS:
Several small sites are better for…
But single large site is better for…
Strategy depends on focus.
- Maximum diversity, and persistence of populations if disturbances to sites are independent and especially where individuals disperse between sites
- Minimising negative impacts of edge effects, and supporting larger populations and allowing long term persistence
