FHSST Biology/Contents/Index/ES/Ecosystems/Resources

2. Resources Humans are separated from other animals in their extensive use of materials to make things. All these materials are derived from Earth. Our bodies use materials in the process of metabolism to facilitate growth and provide energy. Outside of our bodies, we use renewable and non-renewable resources. More abstract resources that we use but do not alter are those such as scenery, wildlife, swimming in dams etc. In every ecological system there are natural limits to the total amount of living matter that can be supported 2.1. Biotic and abiotic resources Water: Occurs in a gas, solid and liquid phase. Usually the most useful in the liquid phase and low in dissolved salts (i.e. fresh water). 97% of all the water on Earth is salt water. 3% of water is fresh water and ¾ of this is locked up in glaciers and ice caps. ¼ is ground and surface water. Surface water is continually moving through the hydrological cycle. Find a simple representation of the hydrological cycle.

The cycle can be regarded as a series of storage tanks, interconnected by the transfer process of evaporation, moisture transport, condensation, precipitation and runoff. Critical water is rainfall on land, as rainfall into the sea is not useful. The distribution of rainfall on land is uneven. Look for diagram of SA’s rainfall patterns.

Some of the rainfall on land is evaporated, some runs into the oceans, some enters the groundwater system. 2.1.1 Biotic 2.1.2 Abiotic

1.1 Ecosphere and Biosphere.

There terms are used as the idea of ‘Nature’ is very different meaning between an ecologist and the ‘man on the street’.

Biosphere: that part of the Earth in which life is permanently possible and which contains all living organisms.

Fundamental ecological variables:

Abiotic factors: Climate, Physico-chemical composition of the environment etc. Biotic factors- Paratisism, predation, food supple etc.

Can be dependant or independent of population density.

Primary periodic factors: temperature and amount of light. Secondary periodic factors: Cyclic variations derived from those primary factors. (e.g. Humidity, plant food supply etc.). Aperiodic factors: Drought, volcanoes etc.

Fundamental ecological variables:

Matter, Energy, Space, Time and Diversity.

1. Matter.

Law of tolerance – there exists a range of concentrations, called the interval of tolerances, in which all physiological processes involving that element can take place normally. E.g. Nitrates in soil.

The law of conservation of matter: In natura there is an almost perfect and permanent recycling of matter, alternating between organic and inorganic forms, which is brought about by the three categories into which living organisms can be assigned: 1. The primary photosynthetic producers, 2. The animal consumers, 3. The animal decomposers.

2. Energy: All living systems, are energy converters more than anything else. The utilisation and conversion of energy occur with more efficiency then even the most perfect human machines. Energy is essential for vital processes at every level: from elementary cellular mechanisms to that of the entire biosphere.

First law: The principle of conservation of energy. Energy can be neither created or destroyed, but only changed from one form to another.

The second law:

No process involving a transformation of energy can take place without a partial degradation of the energy, which passes from a concentrated, ordered form to one that is dilute and unusable (in other words, to heat at a low temperature).

Third law:

The unicyclic flow of energy. Can only pass once through any given trophic level of the food chain – degraded as ir progresses, so that it is gradually dispersed and lost to the surroundings in a non- usable form (entropy). The energy upon which all ecological systems function has one external source: the sun (actually no).

A law of optimisation in the use of energy: all species that occupy a particular ecological niche use the available energy more efficiently than other species having similar requirements but less well adapted to the environmental conditions appropriate to that Niche. Whole ecosystems tend to evolve towards a structure consisting of communities that use the available energy most efficiently.

Lindemann’s Law: Only a fraction of the energy reaching a given trophic level in a community is transmitted to a higher trophic level. Smaller animals generally use more energy (survace area to volume ratio).


Total mass of living organisms which can populate an ecosystem depends directly on the space available.

1. Available area determines the intensity of the competition within and between species. The density of populations can be a limiting factor by being either too high or too low. The distribution of individuals in each species over the available space also plays a fundamental role (random, clumped or uniform). Plant eating forest insects thrive in a homo-geneous distribution of their host species rather than discontinuous afforisitation. Crop monocultures offer opportunities for some pest species to thrive. 2. Time. Concerned in the evolution of every ecological system towards a state of maturity (characterised by the optimum accumulation of biomass and therefore of energy – per unit surface area). During the annual cycle, the length of time during which ecological factors have tolerable values determines the types of community capable of occupying and given environment. Get diagram of succession. Diversity:

Characterises a whole community of living organisms. ‘The richness of a population’ The greater the number of species in a given community, the greater is the degree of saturation of potential niches, and thus the greater is the structural complexity of the food web. Redundancy. – if one species is compromised. Older systems are more diverse.

Ecological principles governing the use of natural resources.

Definition of a resource.

A form of energy and/or matter which is essential for the functioning of organisms, populations and ecosystems. In the case of humans: a resource is any form of energy or matter essential for the fulfilment of physiological, socio-economical and cultural needs, both at the individual level and that of the community. Human/ecosystem use of natural resources involves a permanent transformation of matter. This transformation is the result of a continuous flow and consumption and energy (from sun for biosphere or fossil fuels in regards technological civilization). A resource may consist of one of the various forms of primary energy persent in the ecosphere. In addition, however, it may be defined as anything needed by a living organism such that an increase in its availability leads to an increase in energy flow through the organism, and thus a greater rate of energy conversion.

Principles concerning energy.

a. Production of biomass in a given ecosystem governed by solar radiation. b. Energy is transformed in food webs from one form to another but is neither created nor destroyed. Both in primary producers and in animal consumers, part of the energy available is stored in the biomass, with the remainder being used up in metabolic processes. Plants: only a fraction of the incident solar radiation is converted to biochemical energy though photosynthesis. A large proportion of biochemical energy is used for respiration while rest as biomass. In animals, the energy flow undergoes a greater number of ‘partitions’ than it does in plants. In addition to the energy needed for basal metabolism, and for growth and reproduction, there is a certain amount required for locomotion, in homeostasis, the consumption needed to maintain a constant internal temperature. Some food is never assimilated (faeces). Further consumption of energy into the shape of other excreta and of radiated heat, associated with metabolic processes occurring at all levels or organic activity. The efficiency of energy conversion in animal biomass is low and represents a small percentage of energy consumed. All organisms make optimal use of energy by adopting a energy strategy. One category devotes a high proportion of energy intake to reproduction e.g. field mouse approx ½ energy to gestation.

Large long lived organisms store the majority of the available energy in the growth and reproduction of the adult biomass, only a small fraction going to the offspring, e.g. in the blue whale: 97% of the energy ends up in the biomass of the adult while 3 %T of the energy ends up in the biomass of the child.

a. b c d Solar radiation à Lucerne à Calf à Child.

                            0,24 % * a        8% * b        0.7% *c

Therefore limit to length of food chains.

In terrestrial environments, the longest chains are generally of type:

Plant – herbivore –carnivore –top carnivore.

And the most common of all:

Grass – cattle –humans.

In an aquatic environment, we can have:

Phytoplankton ---zooplankton ---microphagus fish ---predator fish –superpredator fish.


Phytoplanton –zooplankton—anchovy—mackerel—tuna—humans.

Overall energy efficiency of a food chain is a greater the shorter it is.

Phytoplankton –zooplankton—blue whale.

NB Humans could achieve greater use of energy by being vegetarians.

Principles concerning matter:

a. In the light of human needs, no natural resource can be said to exist in unlimited quantities, whether it be mineral or biological. The availability of a resource is restricted by various abiotic and /or biotic factors. Such factors as the spatial distribution of a mineral element or biological molecule (e.g. water), the difficulties of transference from the lithosphere or from the atmosphere and many others, may combine in such a way that many chemical elements and mineral molecules which are abundant on the Earth’s surface become limiting factors for primary and secondary production because of their unavailability. No proportional relation exists between total biomass and productivity. Environments like tropical rain forests or animal species like whales do not exhibit a distinctively greater primary or secondary productivity then more modest ecosystems or species. Ignorance of this led to the almost extinction of certain whale species for example/

b. Both the scarcity of a mineral element and its excess through natural or human pollution, can act as factors limiting the take up of other natural resources. c. ‘Law of the optimum’ – An increase in the availability of a nutrient, does not produce an unlimited increase in productivity. Get graph of ‘Law of diminishing yield’ Two types: A. Stimulating type. B. B. Non-stimulating type susceptible to law of diminishing yield.

Principles concerning space:

a. The space available to any organism or person is limited as can’t use all space in distribution as not all suitable. b. The area available for ensuring that each individual is fed decreases more rapidly than the population density, as the area may be assigned to movement, nesting etc. Esp relevant for humans: roads, housing etc.

Principles governing diversity.

a. The greater the stability of ecological factors, the greater the diversity of the ecosystem. Human activity in a natural ecosystem, because it is unforeseeable and always acyclic, inevitably has the affect of decreasing the species diversity. b. Tine on species diversity: Succession. The diversity of an ecosystem increases as a function of time. c. The biomass /productivity ratio of an ecosystem is proportional to its diversity.

H = K*B/P.

Where H is diversity, B – Biomass P is productivity and K is a constant. P = flow of energy per unit time . It takes a longer time for energy to flow in long food chains and hence linked to diversity.

d. The ratio of B/P grows as a linear function of diversity and/or time up to an asymptotic limiting value. The B/P ratio is low for a field of field of cereal and max in a primitive tropical forest. e. The most diversified ecosystems are the most stable. There will be a larger number of links in the food web and more organisms with redundant functions. f. NB Grasslands and stability (check thesis) and redundancy lookup. Diversified ecosystems exploit less diversified ecosystems. Forest savanna example: Forest animals mostly seek their food in neighbouring open ground (savanna) thereby preventing savanna from evolving to the more diversified stage.

Principled concerning populations.

The law of population growth in the absence of limiting factors: Rate of growth of population with time is observed to remain constant but the speed of growth increases exponentially with time.

The law of population growth with limiting factors: The max speed of growth is attained when the size of the population is half the limiting capacity of the environment.

Stability of populations.

In the stable environment subject only to small fluctuations in its ecological factors, the populations themselves are stable. High diversity carries with it very low levels of wastage because of the great variety o niches occupied by the species forming the community. Such high efficiency in the utilisation of energy in mature and highly diversified ecosystems leaves no room for wastage of resources and there is therefore no surplus which would permit great fluctuations in species populations. Only in species belonging to ecosystems with very simple food chains (lookup lemmings and locust plagues). That sudden explosions of population are experienced.