2.1 Individuals, populations, communities, and ecosystems

• Ecological system composed of individuals, populations, communities, ecosystems

• Parts of Earth where life exists

• Individual organism is member of a species

• Biological species concept: can interbreed and produce fertile offspring

• Allows efficient identification and prediction of characteristics

• Binomial nomenclature: genus (capitalized) + species (lowercase)

• Dichotomous keys, specimen comparison, DNA surveys

• Same species in same area at same time, capable of interbreeding

• Abiotic: non-living physical factors

• Biotic: living components

• Temperature, sunlight, pH, salinity, dissolved oxygen, soil texture

• A niche describes the particular set of abiotic and biotic conditions and resources upon which an organism or a population depends

• An ecological niche is the role of a species in an ecosystem

• The niche comprises all biotic and abiotic interactions that influence the growth, survival and reproduction of a population, including how food is obtained

• Include: some of the parameters of a niche for a named species

• Populations interact in ecosystems by herbivory, predation, parasitism, mutualism, disease and competition, with ecological, behavioural and evolutionary consequences

• Consider: one example of each relationship and consider how the relationships influence the population dynamics of the interacting populations and the selective pressures involved

• Carrying capacity is the maximum size of a population determined by competition for limited resources

• Include: examples of resources that may affect carrying capacity, including biotic and abiotic factors

• Population size is regulated by density-dependent factors and negative feedback mechanisms

• Density-independent factors may influence population size, but density-dependent factors tend to regulate populations around carrying capacity

• In addition to competition for limited resources, include the increased risk of predation and the transfer of pathogens in dense populations

• These are examples of negative feedback returning a population to equilibrium

• Population growth can either be exponential or limited by carrying capacity

• If there are no limiting factors, population growth follows a J-curve (exponential growth)

• When density-dependent limiting factors start to operate, the curve becomes S-shaped

• Consider S-curves and boom-and-bust patterns, such as reindeer on St Matthew Island

• Limiting factors on the growth of human populations have increasingly been eliminated, resulting in consequences for sustainability of ecosystems

• Include: the effects of elimination of natural predators, technological advances, and degradation of the environment

• Carrying capacity cannot be easily assessed for human populations

• This is because of the broad and changing ecological niche of humans

• Include: the idea of populations achieving equilibrium within ecosystems, but human populations being less limited due to mobility of resources

• The expansion of the human niche also takes place through technological advances and changes in consumption

• Population abundance can be estimated using random sampling, systematic sampling or transect sampling

• Estimate population size for non-mobile organisms

• Measures: percentage cover, frequency, abundance

• Estimate population size for mobile organisms

• Lincoln index: Population = (M × N) / R

• Collection of interacting populations within ecosystem

• Location where community, species, population, or organism lives

• Energy and matter can enter and exit

• Community + physical environment interactions

• Natural property of ecosystems

• Inputs balanced by outputs in steady-state

• Some persist for millions of years (e.g., tropical rainforests)

• Can lead to tipping points

• Example: Amazon deforestation reduces transpiration → reduced rainfall

• Keystone species have a role in the sustainability of ecosystems

• There is a disproportionate impact on community structure of keystone species and the risk of ecosystem collapse if they are removed

• Consider: two examples

• For example, purple sea stars controlling mussel populations on the North Pacific coast that would otherwise overwhelm the ecosystem; elephants feeding on shrubs and trees

• The planetary boundaries model indicates that changes to biosphere integrity have passed a critical threshold

• There is an interrelationship between ecosystems and species diversity

• Disturbance of ecosystems due to human activity has led to loss of biosphere integrity

• Extinction rates provide evidence that the planetary boundary for biosphere integrity has been crossed

• To avoid critical tipping points, loss of biosphere integrity needs to be reversed

• Ecosystem damage and loss of species can be slowed by protecting the integrity of ecosystems

• Protecting ecosystems ensures the preservation of the niche requirements essential for the ongoing survival of a species