Ecosystems – what are they ?

(Refer to Essentials of Ecology,G. Tyler Miller)

Ecosystems Levels of organization

Individual/OrganismPopulationCommunityEcosystemBiosphere

an Ecosystem consists of all of the organisms living in a community (or communities) together with the abiotic factors with which they interact

Rocky Shore community – an example• the mix of barnacles, algal mats, herbivorous snails

on rocks etc.• the physical environment (dessication, temp, wave

action) leads to a vertical zonation pattern• predation and competition influence distribution

eg. snails grazing algal spores, predatory snails eating herbivores

• disturbance opens spaces, allows establishment of new species

• different communities result in different locationsRocky Shore

community

Structure of a community is usually the result of many interactions

results from:

– many competitive interactions– complex mutualisms– predators increasing and decreasing– variety of disturbances through time– environmental fluctuations and more!

Biomes – ecosystems & communities on a global scale (Miller Ch 4 Fig 4.8)

• vegetation structure in different parts of the world is similar in similar environments - even though species are different

• biomes are communities with similar structure

Biosphere (ecosphere) - the biosphere (i.e. all ecosystems on earth) is an additional level of organization

• Existence of life depends upon– an energy source (the sun)– oxygen, carbon, nitrogen and other elements,

all of which are part of worldwide geological and chemical cycles

• All ecosystems on Earth are linked via global biogeochemical cycles.

• an ecosystem is all of the organisms living in a community (or communities) together with their abiotic factors

Ecosystem functionthrough

Energy flow Cycling of materials

• A systems approach attempts to understand– the way energy is passed through the system– how nutrients are cycled

• Individual organisms or species can be considered in terms of the function they perform

What does biodiversity actually do ?

biological diversity allows the different ecosystem functions to be carried out

the primary ecosystem functions are to

• Capture• Store• Transfer

Energy Carbon dioxide Nutrients Water

ECOSYSTEMS

ecosystems are a network ofinteractions, beginning withthe PRIMARY PRODUCERS(the PLANTS) andconnecting to herbivores,carnivores, parasites,decomposers

...energy, nutrients & waterare cycled through thenetwork by these differentgroups

Miller Ch 4 Fig 4.6

Flow of energy and materials through an ecosystem

Systems approach to ecosystem function

Essential characteristics of ecosystems

1. Energy flow

Energy flows in a unidirectional way (it does not cycle!) fig 4.13 Miller Ch 4

This requires a continuous input of energy into an ecosystem

Energy source autotrophs heterotrophs

Essential characteristics of ecosystems

1. Energy flow

• Autotrophs (e.g. plants, algae)

organisms capable of synthesizing all their required organic molecules from simple organic substances and an energy source

Essential characteristics of ecosystems

1. Energy flow• Heterotrophs (e.g. animals) organisms that cannot

synthesize complex organic compounds and must feed on organic material formed by other organisms to obtain energy and necessary molecular building blocks for metabolism and growth

Essential characteristics of ecosystems2. Cycling of materials

• Materials (e.g. carbon, nitrogen, phosphorus) are cycled from the abiotic environment, through living organisms, and back to the abiotic environment

• This results from metabolic activities of plants and animals, and organisms such as bacteria and fungi that break down organic matter

Energy in ecosystems• All organisms require energy

– maintenance, growth, reproduction, (and movement)

• The energy driving the biosphere (and all ecosystems) is solar radiation, captured via photosynthesis by autotrophs

• about 1% of visible light converted to chemical energy• about 120 billion tonnes of new organic material produced

each year• about 99% of all organic matter in the biosphere is autotrophs

(i.e. mostly plants)

Sunlight - the source of energy for the biosphere

Miller Ch 4 Fig 4.14

Photosynthesis

Photosynthesis

6 CO2 + 12 H2O C6H12O6 + 6 O2 + 6H2O

Respiration

Energy (from photosynthesis) is released and used by the organism when the complex molecules are subsequently broken down during metabolism

(+ solar energy)

Productivity in ecosystems(Refer to David T. Krohne ;Pg 358-366)

Primary productivity - the rate at which solar radiation is converted into chemical energy by autotrophs (plants) (amount of material or energy per unit time, e.g. g/m2/yr)

Secondary productivity - the rate at which heterotrophs (animals) convert the chemical energy of their food into new tissue

Productivity in ecosystems• However, not all of the energy is converted into

new living tissues– respiration (metabolism) accounts for a large part

• Gross primary productivity - energy fixed in photosynthesis per unit time

• Nett primary productivity - energy fixed in photosynthesis minus energy used in respiration (that is, it is the amount available for harvest at next level)

Productivity in ecosystems

A measure of nett primary productivity is the change in biomass per unit time(but be aware of what may have been lost)

Biomass - the weight of living tissue per unit area (e.g. kg/ha)

What limits primary productivity?

(The factors that limit rate of photosynthesis limit production)

• light• water• temperature• nutrients (N, P, trace elements)

• all are essential - the resource in shortest supply will be the one limiting biomass production

Which are the most productive ecosystems on Earth?

Which are the most productive ecosystems?

Ecosystem Nett primary World primary production production (g/m2/yr) (billion t/yr)

Tropical rain forest 2200 37.4Woodland/shrubland 700 6.0Temperate grassland 600 5.4Desert and scrub 90 1.6Swamp and marsh 2000 4.0Open ocean 125 41.5Upwelling ocean zones 500 0.2Algal beds and reefs 2500 1.6

Productivity through time• Primary productivity will vary seasonally depending

on environmental conditions - ‘growing season’ in agriculture

- tropical vs temperate forests

• Productivity may change with the age of an ecosystem (regenerating vs older)

Young ecosystems - often a greater proportion of young actively growing tissue