Lecture 23 Flashcards
Communities
Two or more species that occur together in space and time. They may interact with each other. Includes all biota.
Assemblages
A group of species that live together with no assumptions made about how or whether they interact with each other
Over time
stable communities maintain consistent species richness and composition. However, change in species composition is the norm in nature. Change is driven by local colonisations and extinction of species. Classic models are underpinned by succession of species. Predictable patterns of change occur in response to disturbances. New communities are being assembled by human activity. New communities are often homogeneous in many parts o the world ‘biotic homogenisation’
Succession
Early ideas related to forest: tree falls down, creating gap for light. Light is unsuitable for certain species, creates high quality environment for other species. Changes in species composition and abundance, growth rates in lower canopy and ground level strata. Dominant species in system change over time. Various biogeochemical processes associated with the presence of certain species also change. New dominant species move in. Equivalent changes often seen with animals, fungi etc.
Pioneer species
Grow in sun, fix N, good dispersal, small seeds, rapid growth, short regen time, poor competitors
Climax species
shade tolerant, slow growth, long-lived, good competitors
Primary succession
Bare area without soil e.g sand-dune, bare rock
Secondary succession
In habitat modified by other species. e.g forest gaps, abandoned agriculture
Facilitation
Early arriving species make environment more favourable for later species
tolerance
Neither negative nor positive interactions between early and late species
Inhibition
Early species inhibit later species
Intermediate disturbance hypothesis
Patchy mosaic of disturbance creates highest diversity
Resiliance
How long before a community returns to an ‘equilibrium’ after disturbance.
Ecosystem
The sum of and interaction between abiotic/biotic factors
Biogeochemical cycle
Energy flows through the biosphere. Materials are recycled. Ecosystem productivity is controlled by efficiency of recycling as well as by energy available. Materials transported in the atmosphere go through global cycles. Some cations move through the soil (local cycles)
