L1 - Global Patterns of Biodiversity
Biodiversity: variety + variability of life on earth
➔ Prioritise conservation efforts
➔ Simplest measure = species richness: number of species in an area nhyi;
Latitudinal gradient of species richness:
Increasing number of species in each taxonomic group from poles to tropics
- Except bats
- Harder to collect data on marine biodiversity patterns -> experience smaller change in
species richness
Poles = Antarctica, Arctic/alpine, Tropics = temperate deciduous forests, temperate grasslands
Low latitude = tropics high latitude = poles
Reverse Latitudinal Patterns:
1. Seabirds: greatest abundance + diversity at high latitudes
2. Lichens: mx diversity in cold regions of boreal forest
3. Microbes = cosmopolitan: live everywhere -> not restricted by geographical barriers
Control of Latitudinal Gradients Hypotheses:
1. Geographical Area Hypothesis: larger surface area in tropics = more species than poles
2. Energy-Species Hypothesis: resource availability + climate -> allows co-existing species
• More energy in tropics = can be used by more organisms
• AET = Annual Evapotranspiration AET > PET
• PET = Potential Evapotranspiration: sum of evaporation + plant transpiration from
earth’s land
• Increasing latitude decreases PET
• decreasing solar radiation decreases PET
a. Productivity Hypothesis: availability of resources dictates number of co-existing
species in an area
More major resources = solar energy + nutrients -> higher plant biomass ->
herbivores -> carnivores
b. Ambient Energy Hypothesis: availability of high temperatures dictates number of co-
existing species in an area
• Low temperature reduces population growth + lowers survival
• Water, temperature, rainfall = limiting factors
• Diversity often declines when resources added to community -> Paradox of
Enrichment: dominant species outcompetes + excludes other species ->
reduces diversity
o Examples: algal blooms in aquatic environments due to
eutrophication, N fertilisation reduces diversity in plant communities
3. Heterogeneity Hypothesis: general increase in environmental heterogeneity towards tropics
Heterogeneity: diversity in habitats
Disproven:
o Only takes place in amphibians
o Latitudinal biodiversity patterns in sea even though there is little heterogeneity
variation
4. Rapoport’s Rule: geographical range of species decreases poles -> tropics
, Low latitudes: narrow range of environmental tolerance
Niche packing: few species with narrow niches
High latitudes: wide range of environmental tolerance
3 Explanations:
a. Climatic variability: greater variability at high latitudes -> more diverse
b. Glaciation: species with high dispersal ability populate north -> wide range
c. Interspecific Competition:
i. Tropics = restricted habitat = more competition = smaller niches + fine
adaptations
ii. Poles = limited by environmental factors = less competition = broader niches
5. Evolutionary Speed Hypothesis: tropics = stable for long time -> allows faster evolution rate
3 traits character
a. Long evolutionary history -> more populations
b. Lack of glaciations -> stable existence of populations
c. Constant warm temperatures
L2 – Measuring Biodiversity
Measures of biodiversity:
1. Species Richness = Alpha Diversity:
= number of species + number of endemic species in each area
2. Species Composition = Beta Diversity:
Compares similarity + differences between areas
Change in species composition between places = opposite of Jaccard Index
3. Phylogenetic Diversity:
How related species in an area are to each other
Find areas with more unique species
Longer branches in phylogenetic tree = higher phylogenetic diversity = more distantly related
4. Functional Diversity:
Diversity in species traits related to function in a community
Elements of biodiversity which influence how ecosystem functions
Hotspots of Species Diversity:
Biodiversity hotspot: geographical location with high species richness
Considering areas of conservation -> overlapping species richness, endemic + threatened species
richness, species agreement
Complementary Approach: conserving as much biodiversity as possible in a limited area of land
available
Uses Jaccard Similarity Index
➔ Higher Simpson index = more even species richness -> higher conservation priority
Ecosystem function: all species have function/dynamics/interactions e.g. stocks of materials, rates of
processes, energy fluxes between trophic levels
➔ Positively related to species richness
Ecosystem service: provides things to humans = life possible + worth living
, 2 species have same function -> one can be removed without affecting ecosystem = lowers species
richness + not functionality
Ecosystem service = functional diversity + ecosystem functioning
L3 – Causes of Local Biodiversity
Regulation of Local Diversity: enable coexistence
1) Equilibrium Theories: evolution + competition develops into stable state
a. Niche Concept: specialisation enables more species to coexist in an area
Different species used different resources -> don’t compete
Tropic community = many species with narrow niches -> resources don’t overlap
Temperate community = species with broad niches -> resources overlap -> increased
competition
b. Heterogeneity Concept: more diverse habitats have more niches
e.g. as tree height increases = more space for insects, plants, birds = tree biodiversity
increases
Problems:
- Mainly followed by animals -> plants compete for same resources
- Resources + conditions not partitioned into discrete packages/niches
- Doesn’t account for most of biodiversity
c. Island Biogeography Theory: Macarthur + Wilson
Central paradigm of island biogeography = determined by extinction + migration
• Discrete, quantified, numerous + bounded communities
Species diversity in oceanic island = island area + distance to mainland
➔ Maximum species richness = when 2 forces overlap = extinction+ immigration =regulated by
area + isolation
- Mainland = Large area = can support larger populations
- Island = Small area = more genetic similarities = more likely to go extinct
• Area -> extinction
• Isolation -> immigration
Biodiversity: variety + variability of life on earth
➔ Prioritise conservation efforts
➔ Simplest measure = species richness: number of species in an area nhyi;
Latitudinal gradient of species richness:
Increasing number of species in each taxonomic group from poles to tropics
- Except bats
- Harder to collect data on marine biodiversity patterns -> experience smaller change in
species richness
Poles = Antarctica, Arctic/alpine, Tropics = temperate deciduous forests, temperate grasslands
Low latitude = tropics high latitude = poles
Reverse Latitudinal Patterns:
1. Seabirds: greatest abundance + diversity at high latitudes
2. Lichens: mx diversity in cold regions of boreal forest
3. Microbes = cosmopolitan: live everywhere -> not restricted by geographical barriers
Control of Latitudinal Gradients Hypotheses:
1. Geographical Area Hypothesis: larger surface area in tropics = more species than poles
2. Energy-Species Hypothesis: resource availability + climate -> allows co-existing species
• More energy in tropics = can be used by more organisms
• AET = Annual Evapotranspiration AET > PET
• PET = Potential Evapotranspiration: sum of evaporation + plant transpiration from
earth’s land
• Increasing latitude decreases PET
• decreasing solar radiation decreases PET
a. Productivity Hypothesis: availability of resources dictates number of co-existing
species in an area
More major resources = solar energy + nutrients -> higher plant biomass ->
herbivores -> carnivores
b. Ambient Energy Hypothesis: availability of high temperatures dictates number of co-
existing species in an area
• Low temperature reduces population growth + lowers survival
• Water, temperature, rainfall = limiting factors
• Diversity often declines when resources added to community -> Paradox of
Enrichment: dominant species outcompetes + excludes other species ->
reduces diversity
o Examples: algal blooms in aquatic environments due to
eutrophication, N fertilisation reduces diversity in plant communities
3. Heterogeneity Hypothesis: general increase in environmental heterogeneity towards tropics
Heterogeneity: diversity in habitats
Disproven:
o Only takes place in amphibians
o Latitudinal biodiversity patterns in sea even though there is little heterogeneity
variation
4. Rapoport’s Rule: geographical range of species decreases poles -> tropics
, Low latitudes: narrow range of environmental tolerance
Niche packing: few species with narrow niches
High latitudes: wide range of environmental tolerance
3 Explanations:
a. Climatic variability: greater variability at high latitudes -> more diverse
b. Glaciation: species with high dispersal ability populate north -> wide range
c. Interspecific Competition:
i. Tropics = restricted habitat = more competition = smaller niches + fine
adaptations
ii. Poles = limited by environmental factors = less competition = broader niches
5. Evolutionary Speed Hypothesis: tropics = stable for long time -> allows faster evolution rate
3 traits character
a. Long evolutionary history -> more populations
b. Lack of glaciations -> stable existence of populations
c. Constant warm temperatures
L2 – Measuring Biodiversity
Measures of biodiversity:
1. Species Richness = Alpha Diversity:
= number of species + number of endemic species in each area
2. Species Composition = Beta Diversity:
Compares similarity + differences between areas
Change in species composition between places = opposite of Jaccard Index
3. Phylogenetic Diversity:
How related species in an area are to each other
Find areas with more unique species
Longer branches in phylogenetic tree = higher phylogenetic diversity = more distantly related
4. Functional Diversity:
Diversity in species traits related to function in a community
Elements of biodiversity which influence how ecosystem functions
Hotspots of Species Diversity:
Biodiversity hotspot: geographical location with high species richness
Considering areas of conservation -> overlapping species richness, endemic + threatened species
richness, species agreement
Complementary Approach: conserving as much biodiversity as possible in a limited area of land
available
Uses Jaccard Similarity Index
➔ Higher Simpson index = more even species richness -> higher conservation priority
Ecosystem function: all species have function/dynamics/interactions e.g. stocks of materials, rates of
processes, energy fluxes between trophic levels
➔ Positively related to species richness
Ecosystem service: provides things to humans = life possible + worth living
, 2 species have same function -> one can be removed without affecting ecosystem = lowers species
richness + not functionality
Ecosystem service = functional diversity + ecosystem functioning
L3 – Causes of Local Biodiversity
Regulation of Local Diversity: enable coexistence
1) Equilibrium Theories: evolution + competition develops into stable state
a. Niche Concept: specialisation enables more species to coexist in an area
Different species used different resources -> don’t compete
Tropic community = many species with narrow niches -> resources don’t overlap
Temperate community = species with broad niches -> resources overlap -> increased
competition
b. Heterogeneity Concept: more diverse habitats have more niches
e.g. as tree height increases = more space for insects, plants, birds = tree biodiversity
increases
Problems:
- Mainly followed by animals -> plants compete for same resources
- Resources + conditions not partitioned into discrete packages/niches
- Doesn’t account for most of biodiversity
c. Island Biogeography Theory: Macarthur + Wilson
Central paradigm of island biogeography = determined by extinction + migration
• Discrete, quantified, numerous + bounded communities
Species diversity in oceanic island = island area + distance to mainland
➔ Maximum species richness = when 2 forces overlap = extinction+ immigration =regulated by
area + isolation
- Mainland = Large area = can support larger populations
- Island = Small area = more genetic similarities = more likely to go extinct
• Area -> extinction
• Isolation -> immigration
