Global patterns of biodiversity

• Drives everything that we have in terms of life on Earth
• It is the net amount of energy fixed by plants (which are autotrophs) but also consider algae which contain chlorophyll
• Relationship between gross primary productivity (total amount of energy fixed by plants) and respiration
• NPP = GPP - respiration
• Can be measured using satellite imagery which is based on the strong reflectance pattern of leaves at differentwavelengths of the elctromagnetic spectrum
• NPP varies based on the season - some areas e.g. tropical rainforests stay highly productive throughout the year
• Controls on NPP
  • Respiration increases as temperature increases
  • Gross photosynthesis doesn't show a linear increase with temperature, there is a plateau above 20 degrees C
  • Net photosynthesis is not a linear relationship with temperature - it increases to around 18 degrees then declines
  • Photosynthesis and light intensity is not linear
  • For grasslands, temperate and boreal environments there is almost a linear relationship - the wetter it gets, the greater the NPP
  • In tropical environments there isn't a linear relationship

• Plants are relatively inefficient in terms of energy fixation through photosynthesis
• Only around 4.5% of light hitting a leaf is transformed into chemical energy in the form of simple carbohydrates
• Maximum efficiencies are reached at low light levels
• At higher levels, photosynthetic efficiency is limited by the amount of CO2
• Not all light is trapped by chloroplasts - it may not reach them but be absorbed by soil or reflected by the plant
• Even if a photon of light reaches a leaf its energy may be used to warm the leaf rather than photosynthesis

• Animals are completely dependent on plants as plants are primary producers
• Primary producers > primary consumers > secondary consumers > tertiary consumers > decomposers
• On average only 10% of energy in any trophic level is passed onto the next level
• But this varies based on the type of organism - birds and mammals are least efficient as they use energy to maintain a constant temperature (around 3% of energy received is assimilated), insects have an energy efficiency of 39% and fish 10%

• Energy fixed by plants in their growth
• Organic material derived from living organisms (plants and animals)
• Consider both above and below ground biomass

• AKA Human Appropriation of Net Primary Production (HANPP)
• 36% of Earth's bio-productive surface is entirely dominated by people
• 40% of terrestrial NPP is apprpriated by humans
• Most HANPP is consumer in wealthy/most populous areas of the world
• But these aren't necessarily the areas where the most energy is produced, so they have to import
• Humans appropriate the biosphere in many ways - land transformation, water use, nitrogen fixation, bird extinction, marine fisheries, CO2 concentration etc
  • Natural capital - all of the benefits we take from ecosystem services
  • Can't put a price on it. but Costanza et al, (2014) estimate between $125 and 145 trillion per year

• AKA latitudinal (global) patterns of biodiversity
• High degree of congruence between mammal and bird diversity (in terms of level of biodiversity in different locations in the world). Low ddegree of congruence between amphibian diversity and mammal/bird diversity
• Latitudinal gradient in species diversity is one of the most universal patterns in global biodiversity
• Lower the latitude, greater the number of species in any given area
• Pattern is found in most taxonomic groups and features persistently through the geological record
• There is not one single causal mechanism

• Biodiversity differences are a product of modern biological and ecological processes
• The Tropics have a large land area so can support more species
• They also have more complex topography and complex community (vegetation) structure present, meaning there are more habitats
  • Greater habitat diversity correlates positively with greater resource gradients and greater available niche space
• Environmental stability also promotes higher biodiversity (if temps are stable, food is likely to be the same all year round which benefits animals looking for food)
  • At lower latitudes, several species can be more specialist and therefore more can be supported by the given resources
• Higher energy is available at lower latitudes
  • This promotes high NPP which promotes high plant species richness which promotes high animal species richness
  • However, the NPP-biodiversity relationship breaks down at smaller scales e.g. estuaries, swamps, marshes, suggesting something more complex is happening
• Regardless, there are strong arguments to suggest primary productivity promotes species diversity...
  • High annual evapotranspiration rates are strongly correlated with high species diversity of plants and animals
  • High evapootransporation rates occur in regions with high solar input and moisture
  • Light (to an extent), heat and moisture are key resources
  • Ability to photosynthesise year round means vegetative food and fruit are always available - many tropical birds, mammals and insects are obligate fruit eaters

• Modern geography differencesin biodiversity reflect past history species evolution and extinction
• Assume modern patterns are not in true equilibrium with modern environmental parameters
• Latitudinal pattern has existed for most of the last 600 million years (Phanerozoic), and more species evolved during this time in tropical than extra tropical regions
• During the Quaternary period there has been repeated habitat fragmentation -  expansion nd contraction of habitats. Might lead to speciation in islands and in others loss of species due to extinction

• Areas which have more species than you would expect them to have by virtue of their climatic and environmental conditions
• Concept made popular by Washington based conservation NGO, Conservation International. Key paper - Myers at al, 2000.
• Various criteria is used to define these, much of which is conservation based
• Two main criteria : endemism (species restricted in their range) and degree of threat (area of primary vegetation already lost).

Endemism criteria:

• Based on vascular plants which are more static than the animal population
• At the second level, you can look at endemics which are vertebrates (but data availability is poor at the relevant level e.g. national data

Degree of threat criteria:

• A hotspot should have already lost 70% of its primary vegetation
• The Mediterranean basin is the area that has lost the most of its primary vegetation, perhaps because it has been subject to intense human activity for at least the last 10,000 years.

Criticisms of hotspots:

• Only consider species richness, doesn't state what thresholds/criteria should be considered
• Narrow view about the 'value' of species - there are other aspects to biodiversity than that
• Missing/patchy data
• Excludes some global biomes e.g. marine
• Does it implicityly justify degredation of non-hotspot areas?