Local patterns of biodiversity

• Energy source e.g. sunlight
• Solvent e.g. water
• The 'right conditions' e.g. temperature, pH
• Raw materials e.g. soil nutrients such as nitrates, phosphorus, potassium, carbon, oxygen
• All of these will impact how plants and animals behave and therefore, where they are found.
• We would expect organisms to follow environmental gradients.

• An organism can survive across a range of environmental conditions, this is called its niche breadth. But it does best in optimal conditions (might expect to have the greatest number of organisms within a species at this optimum).
• Limiting factors are environmental factors that slow down population growth.
  • 'Law' of the minimum (Liebig, 1840) - productivity, growth or reproduction of an organism will be constrained if one or more environmental factors falls below its limiting level.
  • 'Law' of the maximum - population growth may be curtailed by a factor exceeding its upper limit, not usually used.
• Ecological stresses are the external contraints limiting the rates of resource acquisition, growth or reproduction of organisms.
• Need to consider light, water levels/nutrients in water etc... it is rarely one factor that leads to the law of the minimum.

• The entire area in which a species can be found, regardless of whether it is common or rare.
• Differences in abundance across a species' range can be referred to as its density e.g. numbers of individuals per square metre, hectare or km, or per cubic metre in aquatic environments.
• Highest densities are often found in the central portion of a species' range and lower densities at the peripheries This is because density is greatest where the environment provides the best conditions producing the highest carrying capacities.
• It is possible for species' ranges to expand and contract.
  • This can be naturally e.g. Little Egret first appeared in UK in sig. numbers in 1989, first bred in Dorset in 1996 and is now found along the south coast of England but also in northern and western France.
  • It can also occur in response to environmental change e.g. global warming and cooling. Forced to retreat into areas due to interglacials for examples.
  • Conservation strategies might lead to range expansion, but this may need to focus on peripheries as it is from these areas that expansion might occur.
  • Range expansion might also occur due to increaseddeposition of nitrogen (nitrogen fixing), the influence of tourism (seeds might be carried from lower elevations to higher elevations on people's shoes) or grazing. But climate change is the favoured explanation -The Conservation.com, why some plants and animals thrive under climate change.
• This happens to avoid extinction - if a species is not able to expand or contract its range it will go extinct.
• Other species that are expanding their range into the British Isles include the glossy ibis and the spoonbill.

Has a variety of different meanings...

• Determined by the habitat in which a species lives
• The relationship of that species to its environment, especially to other species which share its habitat e.g. as prey/predators, with different species occupying that niche in different habitats. i.e. the role a species plays in its community.
• Related to the availabilty of resources. The configuration of those resources determines which species are present and where a species can live.
• Consider a niche as three dimensional - we have to consider multiple different environmental gradients.
  • Species exist in multidimensional space defined by all the different physical environmental factors that affect their physological functioning and ultimately their abundance.
  • E.g. for a plant these variables might include site elevation, maximum annual temperature, minimum annual temperature, total annual precip, soil nitrogen/organic matter/water capacity/depth/pH etc...
  • The dimensional representation of a species' environment is its niche. It is defined by the total range of environmental variables to which a species must be adapted.
    • Fundamental niche - the entire set of optimal conditions which a species can occupy in the absence of competition. Its geographical equivalent is its potential geographical range.
    • Realised niche - actual set of conditions in which a species normally lives.

• It has been argued that no two species can coexist in the same place, eventually one will outcompete the other.
• Competing species may appear to occupy the same n-dimensional space but frequently they are using resources in different ways so as to avoid competition.
  • This may be related to structure of habitat, temporal use of resources etc...
• If they are competiting for the same resources, then one will overcome the other, leading to extinction, or evolutionary shift towards a different ecological niche.

• Succession usually implies a progressive sequence through time and/or place
• One of the earliest ecological concepts, word first used in 1806 to describe how lakes and ponds turn into meadows and mosses
• Clementsian ideas are at the forefront of vegetation succession
  • Idea that plant communities are somehow more than the sum of their individual species
  • Driven by 6 forces (not all of which are now recognised in the same way)
    • Nudation creates bare land e.g. eruption of lava, glacier retreating
    • Migration and ecesis are the arrival and establishment of organisms at a site e.g. wind blown seeds
    • Competition from interactions of species
    • Reaction leads to modification of the site by organisms
    • Stabilisation is the development of a stable endpoint (i.e. climax community, usually woodlands/forests)
• The word succession implies a direction - a series of 'seres' pr a continuum from an initial or pioneer community to a well developed, mature and perhaps stable community.
  • Might get increasing complexity
  • Will probably get greater biomass
  • May or may not get floristic stability

• Gleason - reductionist
  • Stated it wasn't possible to treat a community of species as a community; you needed to look at each individual species, treated independently and see how it disperses across a variable landscape.
  • This means that predictability is less likely.
• Polyclimax
  • Idea that vegetation will stabilise in different ways into edaphic (soil), physiographic, biotic or anthropogenic climaxes i.e. climate is not all dominant
• Maybe not applicable to a range of environments
• Dominated by European/North American ideas of equilibrium
• Not uniformly agreed, widely contested

• At a local scale, distributions are controlled by...
  • Environmental factors
  • Ecological processes e.g. migration, competition etc
  • Interaction with environmental factors and other species
• Species ranges are dynamic and respond to external forcing factors e.g. climate change, on a variety of timescales