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2. Introduction to Ecology

Nick Reid

Learning objectives

At the end of this topic you should be able to: Explain what ecology is and its relevance to sustainability and farm and catchment

management Understand in broad terms the concept of stocks and flows of energy and matter through

ecosystems, the ways in which ecosystems can change in response to external factors, and the state and transition framework for summarising ecosystem dynamics

Appreciate the critical role of biodiversity for life on earth and a range of views about its importance for agriculture

Key terms and conceptsBiodiversity, consumers, ecoregions, ecosystem dynamics, ecosystem services, ecosystem stability, life history strategies, primary production, state and transition model.

Introduction to the topicAs outlined in Topic 1, ‘sustainability’ is the capacity to continue indefinitely. However, the concept has assumed more in the environmental, resource management and development literature than its literal definition would imply over the past three decades. The environmental concept had its genesis in the World Conservation Strategy (Anon. 1980) that promoted the need for the simultaneous productive use and conservation of natural resources:

Sustainability = Production + Conservation

The Brundtland Report (WCED 1987) elevated the concept to the world stage, defining sustainable development as seeking:

… to meet the needs and aspirations of the present without compromising the ability to meet those of the future.

In fact, many definitions of sustainable development and similar concepts exist (Pearce et al. 1989). Most express the need to consider (Young 1992):1. the effects of present day activities on the future2. the importance of maintaining ecological processes3. the benefits of improving the quality of life now without denying future generations a similar

opportunity.

Agricultural and resource use decision making is complex! Farm developments and resource use decisions all have social, economic and ecological ramifications and big developments can have political ramifications. The regulatory, policy and planning environment is important if primary producers and resource managers want to avoid contravening legal or planning requirements. In order for a particular development to be sustainable:1. Considerations in each dimension (social, economic, environmental) need to be weighed

up2. Impacts need to be deemed acceptable3. No one dimension should be afforded too great a priority in decision making.

RSNR403/503 Sustainable Land Management - 2 - 1©2009 The Australian Wool Education Trust licensee for educational activities University of New England

Deciding what constitutes an ‘acceptable’ impact and ‘too great a priority’ is, of course, part of the difficulty in deciding what development is sustainable.

Young (1992) identified three policy goals for sustainable development – the three ‘E’s:1. Environmental integrity2. Economic efficiency3. Equity (defined to include present and future generations and recognise cultural as well as

economic considerations).

Ecology, economics and sociology thus form the three pillars of sustainability (Di Castri 1995). An integrated understanding of ecology, economics and sociology is important if we are to understand, identify and implement sustainable agricultural and catchment management. This topic introduces you to basic concepts from ecology, while Topic 3 covers economics and Topic 4 deals with sociology. These topics will help you navigate and understand the subsequent unit materials.

In this topic, we define ecology and explain its relevance to sustainability. Ecological concepts important for sustainability are enumerated and illustrated with examples. Hopefully, this is a refresher and not new material for most of you, in which case you can skim this topic and move on quickly.

2.1 What is ecology?Ecology is the study of organisms (including humans) in the places where they live (their habitat or environment) and of the relationships between organisms and their environment (Attiwill and Wilson 2003). Ecology is a very broad science, and includes several well-defined disciplines partly within it, including the applied disciplines of agronomy, forestry, range management and animal science. Since ecology is concerned with the interactions of organisms with the biophysical environment, the related disciplines of soil science, hydrology, resource engineering and meteorology are often important in ecology.

Ecology is studied at a wide variety of different levels of organisation or scales. These are (Attiwill and Wilson 2003):

Organism – here, the focus is on the relationship of an individual organism with its abiotic environment (temperature, moisture, light, soil etc.)

Population – groups of individuals of the same species in a given area; ecologists are interested in the biotic and abiotic factors that affect a population’s size and distribution

Community – all the populations of different species in an area, with a focus on community structure, composition and the biotic interactions between populations, such as predation and competition

Ecosystem – a community together with its abiotic environment; here, the focus is on function, that is the pools and fluxes of energy and matter within and between biotic and abiotic components

Ecoregion – recurring patterns of ecosystems, associated with characteristic combinations of soil and landform (Brunckhorst 2000); ecosystems within an ecoregion are more similar to each other than to ecosystems elsewhere

Biosphere – all of the Earth’s organisms interacting with each other and the global environment.

Populations, communities and ecosystems are often arbitrarily defined for convenience. One researcher might define the population of European foxes (Vulpes vulpes) on several neighbouring sheep properties near Armidale, NSW, as the object of their research. Another might be interested in the population of foxes across the whole of NSW.

Recent legislative and policy initiatives have begun to formally define ecological populations, communities, ecosystems and ecoregions. For instance, recent legislation enacted federally as well as in NSW and Queensland provides for the listing and protection of ‘threatened’ ecological populations, communities and regional ecosystems (Table 2.1). Ecoregions have been defined across the country in the Interim Biogeographic Regionalisation of Australia

(Thackway and Cresswell 1995; Figure 2.1).

2 - 2 – RSNR403/503 Sustainable Land Management©2009 The Australian Wool Education Trust licensee for educational activities University of New England

Table 2.1 Some examples of threatened ecological populations, communities and regional ecosystems under Commonwealth and NSW biodiversity legislation. Source: Adapted from Anon. (1999) and Anon. (1995).

Jurisdiction and Relevant Statutes

Populations Species Communities and Ecosystems

Commonwealth: Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) – see Anon. (1999).

1. Yellow-spotted Tree Frog - endangered species listing

2. Regent honeyeater - endangered species listing

1. Narrow-leafed peppermint – endangered community listing

NSW: Threatened Species Conservation Act – see Anon. (1995).

1. Australian brush-turkey population, Nandewar and Brigalow Belt South bioregions -endangered population listing

2. Tusked frog population, Nandewar and New England Tablelands bioregions - endangered population listing

1. Black-necked stork - endangered species listing

2. Swainsona sericea (a shrub) - vulnerable species listing

Ribbon gum - mountain gum - snow gum grassy forest/woodland of the New England Tableland Bioregion - endangered ecological community listing

2. White box - yellow box - Blakely's red gum woodland

Figure 2.1 The biogeographic regionalisation of Australia into ecoregions (Thackway and Cresswell 1995). ‘Bioregions’ in the figure are more correctly referred to as

‘ecoregions’ (Brunckhorst 2000). Source: DEH (2005).


2.2 Why is ecology relevant to sustainability?Intergenerational equity lies at the heart of the Brundtland Report’s definition of sustainable development (WCED 1987). A major requirement of sustainable development is that the present generation should ensure that the health, diversity and productivity of the environment is maintained or enhanced for the benefit of future generations. Since ecology and related disciplines are the principal sciences concerned with managing the biophysical environment, ecology assumes a central role (along with economics and sociology) in understanding, explaining and predicting the results of human manipulation of the biosphere.

2.3 What ecological concepts are relevant to sustainability?

Several key ecological concepts are vital to understanding environmental management: (1) productivity, (2) biodiversity, (3) ecosystem services, (4) ecosystem dynamics, and (5) life history strategies.

(1) Ecosystem productivity The primary focus of ecosystem ecology is the stocks and flows of energy and matter between the different biotic and abiotic components of ecosystems (Smith and Smith 2003). Organisms are either primary producers or consumers. Primary producers (or autotrophs) are largely green plants which use the sun’s energy in photosynthesis to transform inorganic compounds (CO2 and H2O) into organic compounds. Consumers (or heterotrophs) use the organic compounds produced by producers for food. A class of consumers called decomposers (or detritivores) in the soil recycle the complex organic compounds in dead organisms and organic wastes back into simple inorganic compounds for re-use by producers (Figure 2.2). In addition to the decomposers, consumers are divided into herbivores (those that eat plants) and carnivores (those that eat other consumers).

Figure 2.2 Schematic diagram of the main components of a grazing ecosystem – the producers or plants (and their symbionts); the consumers or grazers and decomposers; soil, and external influences, principally climate and management. The arrows indicate

the direction of influence of the interconnections between components and external influences. Source: Hutchinson (1992).

Ecosystem production involves the fixation and transfer of solar energy and its accumulation in plant biomass (Smith and Smith 2003). The rate at which radiant energy is converted by photosynthesis to plant biomass is referred to as primary productivity. Gross primary productivity is the total rate of photosynthesis or energy assimilated by plants. Net primary productivity is the rate of autotrophic energy capture less the energy used in plant respiration:


Net primary Gross primary Autotrophic productivity = productivity ─ respiration (2.1) (NPP) (GPP) (R)

Productivity can be expressed either in terms of energy or dry organic matter accumulation through time (e.g. kJ/m2/yr or t/ha/yr). Net primary productivity accumulates over times as plant biomass (the amount of organic matter present at a given time). Biomass or primary production is usually expressed as mass of organic matter per unit area (e.g. g/m2).

Net primary production is the biomass available to consumers. The simplest method of measuring net primary production is the harvest method (Krebs 1985). The amount of plant material produced in a unit of time (ΔB) is the difference in the amount at times 1 (B1) and 2 (B2):

ΔB = B2 – B1 (2.2)

However, two possible biomass losses must be recognised, losses due to the death of plants and plant parts (L), and losses to consumers, both herbivores and detritivores (G):

NPP = ΔB + L + G (2.3)

This equation may be applied to the whole plant or just aerial production (‘tops’) or root production.

Figure 2.3 shows energy flow through a short-grass prairie in the South-West US. Note that the most conspicuous animals are the least important energetically. Birds and mammals contribute almost nothing to production and very little to consumption. Above-ground insects contribute a greater amount, but the most important consumers are the soil animals, especially nematodes which consume more than half the plant tissue in these lightly grazed grasslands. By comparison, in grazed phalaris (Phalaris aquatica)/white clover (Trifolium repens) pastures near Armidale, NSW, the ratio of NPP flowing to sheep and the invertebrate decomposer chain is reversed (Figure 2.4). Almost 60% of the NPP is consumed above-ground by the sheep stocked at 10 sheep/ha.

Figure 2.3 (a) Food web and (b) magnitude of the primary and secondary production and consumption in short-grass prairie in the south-west USA. All values are expressed as

energy. Source: Krebs (1985).

(a)


Figure 2.4 Annual energy budgets for sheep (10 sheep/ha) and invertebrates in a phalaris-white clover pasture near Armidale, NSW from 1971-74. I = intake, FU = excreta,

CG = combustible gases, R2 = heat production, and P = production. Source: Hutchinson and King (1980).

(2) BiodiversityBiodiversity means ‘the variety of life’ and refers to the variety of plants, animals, fungi and microbes at the scale of genes, species, ecosystems and ecoregions. The conservation of biodiversity is important for four reasons (SEAC 1996):

1. Ecosystem services. Biodiversity underpins the ecological processes that make life on earth possible and support and sustain us. Healthy functioning ecosystems comprised of a myriad of organisms and their physical environment, are responsible for the atmosphere, climate, fresh water, soil formation, nutrient cycling and waste breakdown. Biodiversity is also essential for controlling most pest plants, animals and diseases and for pollinating crops

2. Ethics. Some people believe that all species or organisms have an inherent right to exist. Others believe that biodiversity belongs to the future as well as to the present, and that no species or generation has the right to appropriate biodiversity for their exclusive use or to squander it


3. Human culture and aesthetics. Biodiversity can have spiritual and emotional values for people such as beauty, tranquillity and isolation. Many people place a high value on native plants and animals and the ecosystems they form, contributing to our sense of cultural identity as well as providing outdoor recreation opportunities. Biodiversity is also important to some for spiritual sustenance, enrichment, inspiration or renewal

4. Economics. Some elements of biodiversity have economic value and generate wealth. Australian plants and animals attract tourists and provide food, medicines and other pharmaceutical products, energy and building materials. Industries based on ecosystem goods such as commercial fishing, the harvest of plants and animals in the wild, and nature-based tourism are worth many billions of dollars in Australia.

Biodiversity emerged as an issue in the 1980s with the realisation of the magnitude of the global impacts of human activities (Smith and Smith 2003). Human impacts can be positive or negative on different elements of biodiversity. The challenge is to balance the exploitation and destruction of biodiversity on the one hand with its conservation, to ensure that human welfare now and in the future is not compromised. This is no easy matter, due to the many value judgements and the diversity of public and private interests involved.

(3) Ecosystem servicesOrganisms in natural and modified ecosystems sustain all life on earth through an array of ecological processes and functions operating at the scale of molecules to the biosphere. Ecological processes and conditions that sustain ecosystems, produce goods and benefits for people, and recycle wastes, are called ecosystem services.

Table 2.2 provides a list of ecosystem services common in agricultural catchments in eastern Australia. These services are generated by the management activities of some resource users and consumed by others. Industry may positively or negatively impact on the provision of ecosystem services that are required by others. While little is known about some of these, the challenge for industry and resource users is clear: to maintain or enhance ecosystem services and the biodiversity that generates them either out of self-interest or for the public good. Conflicts are likely where resource users can maximise profits by depleting the supply of ecosystem services required by others.


Table 2.2 Thirteen ecosystem services common in agricultural catchments in eastern Australia. Source: Binning et al. (2001), Reid et al. (2003).

Ecosystem Service Description1. Natural pest control Service provided by beneficial vertebrates, invertebrates and

microbes in controlling pests and pathogens2. Maintenance of soil health

Continued capacity of soil as a rich mix of mineral particles, biota, organic matter, gases, water and nutrients, to sustain biological production and control the water balance

3. Water filtration Service provided by soil, microbes and terrestrial and aquatic vegetation in filtering water of sediment, assimilating and removing nutrients, and destroying water-borne pathogens harmful to humans or livestock

4. Prevention of soil erosion

Service provided by vegetation, litter and soil biota in protecting soil from erosion, by increasing infiltration, interception and evaporation and reducing and slowing runoff

5. Waste absorption and breakdown

Service provided by decomposer chain and microbes in soil and aquatic ecosystems in breaking down organic matter, recycling nutrients in bio-available forms, and converting pesticide residues into harmless compounds (‘bioremediation’)

6. Maintenance of river flows

Service provided by mosaic of land and water uses, soils, vegetation, waterways and infrastructure in a catchment, and their management, in regulating the quantity, quality and timing of river flows

7. Maintenance of groundwater levels and quality

Service provided by mosaic of land and water uses, rocks, soils, vegetation and waterways in a groundwater catchment, and their management, in determining yield and quality of groundwater

8. Maintenance and regeneration of habitat

Ecological processes that permit the reproduction, recruitment, growth and senescence of terrestrial, riparian and aquatic vegetation suitable for dependent species of flora and fauna

9. Maintenance and provision of genetic resources

Biological processes responsible for creating and perpetuating genetic variation inherent in individuals, species and ecosystems

10. Regulation of regional and global climate

Service provided by terrestrial and marine biota in regulating atmospheric composition and evapotranspiration, affecting global and regional climate

11. Provision of shade, shelter and barrier effect

Service provided by tall vegetation, ameliorating extremes in weather and climate at paddock scale, and intercepting and filtering air-borne particles through impaction

12. Pollination Fertilisation of flowers by pollinators, allowing seed and fruit production and critical to plant regeneration

13. Life fulfilment Provision of sense of personal identity or place, existence value, cultural, intellectual and spiritual inspiration or renewal, aesthetic beauty, serenity and scientific opportunity


(4) Ecosystem dynamicsAccording to the soil scientist Hans Jenny (1961), an ecosystem (E) at a given point in space and time consists of vegetation (v), animals (z) and soils (s) and is a product of climate (cl), the organisms present (o), relief (r), parent material (p), time (t) and other unspecified factors (…):

E,v,z,s = f(cl,o,r,p,t …) (2.8)

The other factors can be both inputs (both natural, e.g. fire, dust deposition, and artificial, e.g. domestic livestock, fertilisers, pesticide applications etc.) and outputs (e.g. removal of animal products). These factors include the options for ecosystem management, such as use of fire, manipulation of grazing pressure etc. (Whalley 1994). Implicit in this concept of ecosystem function is that ecosystems can vary or change in space and time in response to a wide variety of factors. Ecosystems vary in composition, structure and function due to changes in climate, aspect and soil type. Ecosystems also vary through time, as plants germinate, grow, dominate and ultimately die. In south-eastern Australia, mountain ash (Eucalyptus regnans) lives for several hundred years. However, in the absence of fire, rainforest develops in the understorey beneath the eucalypt canopy. When the over-mature mountain ashes eventually die, the once hardwood-dominated forest turns into a self-replacing rainforest (Noble and Slatyer 1981). Change in the structure and composition of ecosystems through time is called succession.

State and transition models are used to summarise our understanding of the dynamics of particular ecosystems (Westoby et al. 1989). The state and transition framework permits the vegetation at a point in space to be described as a set of discreet ‘states’ and ‘transitions’ between states. In some instances, it is convenient to recognise ‘transient’ states where the vegetation does not persist indefinitely but changes into one or other persistent state. ‘Transitions’ between states are triggered by natural events (such as weather or wildfire) or by management (changes in stocking, burning, fertilisation, plant introduction or removal etc.). Often a combination of these may be needed to effect a transition. For instance, careful grazing management is required after sown pasture establishment on the Northern Tablelands of NSW, otherwise the sown species are lost and the pasture changes to a volunteer sward (Hutchinson and King 1999).

The state and transition framework is a practical way to organise information about ecosystem dynamics but is not based on theory (Westoby et al. 1989). Management significance rather than theoretical considerations should thus dictate what states to recognise in a given situation. An example of a state and transition model for native and sown pastures on the Northern Tablelands of NSW is shown in Figure 2.5, and other examples are provided in the readings.

(5) Life history strategies Organisms vary markedly in their life history (Begon et al. 1986). Some microbes live for a few hours, some trees live for millennia. Some organisms reproduce once in their lives, others reproduce seasonally for hundreds or thousands of years. The females of some species only ever have one or a handful of young, other species spawn millions of progeny. An organism’s life history is its lifetime pattern of growth, development and reproduction. Natural selection has favoured the co-occurrence of particular life history traits in a given habitat, and a set of adaptive traits evolved in response to a particular set of environmental conditions is called a ‘strategy’.


Figure 2.5 State and transition model for natural and sown pastures on the Northern Slopes and Tablelands of New South Wales. Arrows indicate transitions produced by:

heavy year long grazing plus increased soil fertility (———), drought or improper grazing (– – – –), seeding plus superphosphate addition (---------), regular winter burning (●●●●●●)

and heavy summer grazing (oooooo). Source: Lodge and Whalley (1989).

Grime (1979) developed a classification of habitats and plant life histories outlined in Figure 2.6. Habitats are viewed in terms of varying levels of disturbance (e.g. due to grazing, cultivation, flooding etc.) and environmental stress (e.g. shortages of water, nutrients etc.). When disturbance is rare and resources abundant, a competitive strategy is likely to be successful. When disturbance levels are high but conditions benign, a ruderal (weedy) strategy is appropriate. When resources are scarce and disturbance uncommon, a tolerant strategy is advantageous. Vascular plants find it difficult to survive in high-stress, high-disturbance environments (e.g. the sea-shore, a frequently used path etc.)


Figure 2.6 Grime’s (1979) classification of habitats and life histories. Source: Begon et al. (1986).

The importance of disturbance, stress and interspecific competition are evident in the dynamics of many grazing systems. In conservatively grazed (10 sheep/ha), well fertilised phalaris-white clover pastures on the Northern Tablelands of NSW, phalaris is highly competitive and can dominate the pasture sward for decades (Figure 2.7). Under high stocking rates (30 sheep/ha), however, severe grazing pressure combined with periodic (1 in 10 year) drought will eliminate phalaris. Under these conditions, a variety of (ruderal) annual plants almost entirely replace the phalaris. In this example, the interaction between grazing disturbance and drought stress is crucial in the replacement of a competitive plant species by ruderals.

A knowledge of the life history strategies of common pasture grasses and forbs can help to predict their response to pasture fertilisation and grazing pressure (Hill et al. 2005). For example, on the Southern Tablelands of NSW, phalaris is a stress-tolerant competitor that is abundant in infertile pastures, yet responsive to fertiliser and dominant in fertilised, laxly grazed pasture. By contrast annual brome grass (Bromus molliformis) is a competitive ruderal, doing poorly in infertile soils but responsive to fertiliser and abundant in fertilised pastures irrespective of grazing pressure. The feature that distinguishes these two competitive species from others is their tall stature, the advantage of which is evident under low grazing pressure. Sub clover (Trifolium subterraneum) is a low-stature stress-tolerant ruderal that dominates most pastures but concedes pasture dominance to the taller species in fertilised, laxly grazed systems.


Figure 2.7 Stability over 28 years of sown perennial grass and invasion by annuals in well-fertilised pastures sown to phalaris and white clover near Armidale, NSW. Sites were

set-stocked (low stocking 10 sheep/ha, high 30 sheep/ha) and experienced two major droughts. Source: Hutchinson (1992).

2.4 Biodiversity and sustainabilityOver the past three decades, ecologists have debated the role of biodiversity in contributing to functional properties such as ecosystem productivity, stability and sustainability. Here, we examine the proposition that biodiversity is important for these ecosystem properties. Subsequently, we see that ecological generalisations about agricultural and natural systems are not necessarily relevant to intensively managed paddocks where farmers and graziers routinely intervene with careful choices of species, inputs and grazing management.

The diversity-productivity debateDoes ecosystem productivity depend on its biodiversity? There are two reasons why the number of plant species in an ecosystem should influence its productivity (Tilman 1997). The first is due to a sampling-competition effect. In any given sample of species, one will be the most productive, another will be the second most productive, and so on. Because plant species compete, the most productive species will tend to dominate a stand in which it is present. All else being equal, the probability of having a highly productive plant species present will increase with plant diversity. This should cause total plant community productivity to increase, on average, with plant diversity.

The second reason for biodiversity influencing ecosystem productivity is due to species complementarity (Tilman 1997). Differences among species in resource acquisition and use allows diverse communities to more fully utilise limiting resources (e.g. soil moisture, light, temperature, nitrogen (N) etc.). For instance some plant species are physiologically and morphologically adapted to grow best during cool wet weather, whereas others grow better in hot dry weather. If a cool-season and a warm-season species grow together, their complementary features can lead to greater total primary productivity than with either species alone. Harper (1977) found the greatest increases in production in two-species plots came in mixtures of markedly different species, such as a grass and a legume.


Numerous experiments have been conducted growing two or more crop species together (Tilman 1997) and they show that intercrops can generally be designed which will outyield sole crops (Swift and Anderson 1993). The basis for these effects varies (Tilman 1997), and can be due to the provision of N in the presence of a legume, greater nutrient cycling and nutrient availability due to the greater diversity of decomposers present, a greater diversity of natural predators and parasites to attack crop pests, and more efficient spatial or temporal utilisation of limiting resources. The few experiments testing the productivity-biodiversity hypothesis in natural systems support the relationship (Figure 2.8).

Figure 2.8 (a) Average aboveground plant productivity (g/pot) in a greenhouse experiment by Naeem et al. (1995) in which random draws were used to select two, four

or eight-species subsets from a pool of 16 British grassland plant species. There were 64 monocultures (four replicates of each of the 16 species), 20 replicates of two-species

pots, 30 replicates of four-species pots, 40 replicates of eight-species pots, and 10 replicates of all 16 species. (b) The dependence of productivity as estimated by total plant cover, on plant species richness in a field experiment in which from one to 24

prairie plant species were added to plots. Values are means ± 1 s.e.m. for each level of species richness. Source: Tilman (1997).

The Diversity-stability debateDoes the stability of an ecosystem depend on its biodiversity? All ecosystems experience natural variations and disturbances such as drought, floods, unusually hot or cool growing seasons, pest and disease outbreaks, fire, and so on (Tilman 1997). Ecosystems respond differently to disturbance. Some are fairly stable, while others suffer a marked loss of productivity due to the disturbance.


A test of the diversity-stability hypothesis was provided by a severe drought in the mid-western USA in 1988. The drought caused plant productivity in 207 permanent grassland plots to fall, on average, by more than half of the pre-drought level. During the drought, the productivity of the most species-poor plots fell to about one-twelfth of their pre-drought level, whereas the most-species rich plots only suffered a reduction in production of a half (Figure 2.9). Moreover, the more diverse plots had less year-to-year variation in productivity in non-drought years. This evidence supports the notion that diversity increases the resistance of ecosystem productivity to perturbation and that biodiversity has ‘insurance value’ in helping to minimise the cost of unpredictable events (Tilman 1997).

Figure 2.9 Mid-western USA grassland production in plots in a drought year (1988) expressed as a fraction of their production in a good season (1986) and plotted against

the number of species per plot. The numbers indicate the number of plots with that species richness in 1986 and are placed on the graph at the mean value of the production

ratios (± 1 s.e.m., n = 207 plots). Source: Tilman (1997).

Diversity and

ecosystem sustainabilityTilman (1997) argued the case that biodiversity increases ecosystem sustainability, although no large-scale field tests of the hypothesis have been designed to date. We have already seen that diversity increases ecosystem productivity and stability, which are important criteria of ecosystem sustainability. The morphological, physiological and other differences between species may also allow an ecosystem containing a large number of species to more fully exploit limiting resources (Tilman 1997). The more efficient utilisation of limiting resources should decrease their availability in the environment. For soil nutrients and soil moisture, this would minimise the amounts that leach through soil and into groundwater. Thus more diverse ecosystems may also be more retentive of nutrients and moisture (less leaky) and therefore more productive. Therefore, more diverse ecosystems may well be more sustainable, all other things being equal.

Relevance of these generalisations back on the farThe generalisations about multi-species assemblages above refer to random selections of agricultural or naturally occurring plants, or to species assemblages growing naturally. Accordingly, they may be relevant in Australia’s rangelands and in native pastures in higher rainfall environments where growers are reliant on the native vegetation for production.


In higher rainfall environments, however, many graziers are interested in selecting the most productive species for a given paddock rather than relying on natural pasture composition or a random, less-productive selection of sown species. Near Armidale, NSW, well-fertilised phalaris-white clover pasture consisting of just two sown species is more productive and profitable than adjacent degraded pasture consisting of many different volunteer species (Scott et al. 2000). The phalaris-white clover pasture uses more water and leaches less nitrate, owing to the deep roots of the phalaris. Thus, although more species may lead to greater productivity, stability and persistence in agricultural and natural or semi-natural systems where the species are chosen at random or occur naturally, artificial systems based on selecting the most productive species for a given situation can produce contrary results.

Readings There are numerous textbooks and references available which deal with the detail covered in this topic. Five main readings are recommended for this topic. A number of other key resources are provided in the reference list and in the useful web links on CD.

The following readings are available on CD:1. Chapin, F.S.I., Matson, P.A. and Mooney, H.A. 2004, ‘The ecosystem concept’, in Principles

of Terrestrial Ecosystem Ecology, Springer, pp. 3-17. An expanded view of the ecosystem concept.

2. Williams, J., Read, C., Norton, T., Dovers, S., Burgman, M., Proctor, W. and Anderson, H. 2001, ‘The meaning, significance and implications of biodiversity’, in Australian State of the Environment: Biodiversity, Department of the Environment and Heritage, Canberra, pp. 9-18. Available at: http://www.deh.gov.au/soe/2001/biodiversity/pubs/part02.pdf. This report describes the significance of biodiversity to an Australian audience.

The following readings are not provided on CD:1. Commonwealth of Australia 2002, Australian Terrestrial Biodiversity Assessment 2002,

National Land and Water Resources Audit, Canberra. Available at: http://audit.ea.gov.au/ANRA/vegetation/docs/biodiversity/bio_assess_contents.cfm First ever national stocktake of selected components of Australian biodiversity.

2. Ludwig, J., Tongway, D., Freudenberger, D., Noble, J. and Hodgkinson, K. 1997, Landscape Ecology: Function and Management, CSIRO, Collingwood, 158 pp. This book describes the critical role of small-scale patchiness in the ecosystem function of semi-arid rangelands in space and time. The implications of ecological patchiness for range management, livestock production and biological conservation are emphasised.

3. Townsend, C.R., Begon, M. and Harper, J.L. 2003, Essentials of Ecology, 2nd Edition, Blackwell, Malden MA, 530 pp. An up-to- date introductory textbook on the science of ecology.

ActivitiesAvailable on WebCT

Multi-Choice QuestionsSubmit answers via WebCT

Useful Web LinksAvailable on WebCT

Assignment QuestionsChoose ONE question from ONE of the

topics as your assignment. Short answer questions appear on WebCT. Submit your answer via WebCT


Summary This topic provides a refresher to the science of ecology for those who need it. It explains its importance to the concept of sustainable agricultural and catchment management.

Ecology is the study of the interactions between organisms and their environment. Since sustainable development involves exploiting resources in the present without diminishing the opportunities available to future generations, ecological understanding is necessary for utilising and conserving the environment and its resources. Ecologists are concerned with living systems across a broad range of scales (from individual organisms to the biosphere) and with the fluxes of matter and energy between biotic and abiotic components. Changes in ecosystems due to external influences (e.g. management, climate) are often important, and a state and transition framework is used to convey information about ecosystem dynamics. The ecological responses of individual populations can be understood in terms of life history strategies and the ability of species to cope with stress, disturbance and competition. Biodiversity (the variety of life) is important for ecosystem productivity, stability and sustainability in unmanaged situations, but perennial pastures based on the most productive species in a given situation means one or a few species can also perform well in terms persistence and profitability.

ReferencesAnon, 1980, World Conservation Strategy: Living Resource Conservation for Sustainable

Development, International Union for Conservation of Nature and Natural resources, United Nations Environment Program and World Wildlife Fund, Gland.

Anon 1995, Threatened Species Conservation Act 1995 No 101, retrieved 1st November 2006 from http://www.legislation.nsw.gov.au/viewtop/inforce/act+101+1995+FIRST+0+N.

Anon 1999, Environment Protection and Biodiversity Conservation Act 1999, retrieved 1st November 2006 from http://www.frli.gov.au/comlaw/Legislation/ActCompilation1.nsf/current/bynumber/019B48F4E8C92609CA25700000090254?OpenDocument&mostrecent=1.

Attiwill, P. and Wilson, B. 2003, Ecology: an Australian Perspective. Oxford University Press, New York.

Begon, M., Harper, J.L. and Townsend, C.R. 1986, Ecology: Individuals, Populations and Communities, Blackwell, Oxford.

Binning, C., Cork, S., Parry, R. and Shelton, D. 2001, Natural Assets. An Inventory of Ecosystem Goods and Services in the Goulburn Broken Catchment, CSIRO Sustainable Ecosystems, Canberra.

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Glossary of Terms

Autotrophs Organisms that produce organic material from inorganic chemicals and some source of energy

Biodiversity The variety of genes, species and ecosystems

Competition Any interaction that is mutually detrimental to both participants, occurring between species that share limited resources

Consumer Any organism that lives on other organisms, dead or alive

DecomposerOrganism that obtains energy from the breakdown of dead organic matter to simpler substances; most precisely refers to bacteria and fungi

Detritivore Organism that feeds on dead organic matter; usually applies to detritus-feeding organisms other than bacteria and fungi

Ecosystem The biotic community and its abiotic environment functioning as a system

Ecosystem services The benefits to humans from living systems, the goods they provide and the ecological processes and conditions they mediate

HeterotrophsOrganisms that are unable to manufacture their own food from inorganic materials and thus rely on other organisms, living and dead, as a source of energy and nutrients

Life history strategy An adaptive set of traits that enhance an organism’s fitness in the environment in which the traits evolved

Primary production Production by green plants over time

RuderalOne of three principal life history strategies recognised by Grime (1979) and characterising plants adapted to frequently disturbed, low-stress habitats

State and transition model

A description of the contrasting types of vegetation that can occur in a given place and of the sets of coincidental ecological factors required to cause the succession of one type to another

Stress-tolerantCapable of surviving and reproducing under conditions of inadequate resources (e.g. light, moisture, nutrients) in which most vascular plants could not

Sustainability The capacity for a system to persist indefinitely


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