- 1 -

AN INTRODUCTION TO TERRESTRIAL ECOLOGY

by D. A. Eng l i s h and R. H. Ward.

During the l a s t f i f t y years ecology has advanced from a merely observational study, i n t o a science that incorporates a l l that i s basic to b i o l o g y . The extent of ecology becomes apparent when a simple d e f i n i t i o n i s considered: - Ecology is the study of animals and plants in their natural habitats, and the investigation of their inter-relation­ships, and their dependence on their environment.

In order to study any organism i n i t s n a t u r a l h a b i t a t i t must be c o r r e c t l y i d e n t i f i e d , which involves a knowledge of taxonomy. The dependence on the environment i s r e f l e c t e d i n the organism's e x t e r n a l and i n t e r n a l s p e c i a l i s a t i o n . This can only be assessed when one i s f a m i l i a r with morphology and anatomy. Furthermore to understand the processes underlying the s p e c i a l i s a t i o n brought about by environmental and hereditary f a c t o r s a groundwork i n physiology and genetics i s necessary. The i n t e r - r e l a t i o n s h i p s of organisms comprise one of the most e x c i t i n g f i e l d s of e c o l o g i c a l study. As a r e s u l t of s p e c i a l i s a t i o n i n zoology and botany the importance of these i n t e r - r e l a t i o n s h i p s i s not r e a l i s e d . These i n t e r - r e l a t i o n s h i p s are used i n the f i e l d of applied ecology, which i s becoming an ever more important science. The prime example of t h i s i s b i o l o g i c a l c o n t r o l . Moreover the dependence of organisms on t h e i r environment involves both p h y s i c a l and b i o t i c f a c t o r s of the environment.

With the r e a l i s a t i o n of the above f a c t s , ecology becomes more than casual observation and plays an ever i n c r e a s i n g r o l e i n the b i o l o g i c a l sciences.

SOME ECOLOGICAL CONCEPTS

Ecology being a science must base i t s study around a framework of concepts. The concepts of environment, h a b i t a t and ecosystem can be reg rded as b a s i c a l l y important.

The environment

The environment is a continuously changing complex of factors which are interacting directly and indirectly with the organism. These environmental f a c t o r s can be described as those that a f f e c t the f e r t i l i t y , l o n g e v i t y , growth and s p a t i a l p o s i t i o n of an organism. Environmental f a c t o r s may be grouped as follows (Browning 1963): -

1. Climate: - e. g., L i g h t , humidity, temperature, wind, r a i n , e t c . 2. Resources: - e. g., M i n e r a l s , water, food, substrate, gases, s h e l t e r ,

e t c . 3. Members of the same species: - Competition, gregariousness, e t c . 4. Members of other species: - e. g., Predators, p a r a s i t e s , competition,

symbiosis, e t c . 5. Hazards: - e. g., Floods, f i r e , e ruptions, e t c

- 2 -

A l l environmental f a c t o r s , however, do not n e c e s s a r i l y comprise the environment of an organism as only some of them enter i n t o the r e a c t i o n system. Environmental f a c t o r s i n d i r e c t contact with the organism are known as d i r e c t f a c t o r s , some of which, termed l i m i t i n g f a c t o r s , r e s t r i c t growth and d i s t r i b u t i o n of an organism. L i m i t i n g f a c t o r s operate by exceeding the tolerance of the organism to that f a c t o r . Probably the best example of a l i m i t i n g f a c t o r i s water. When there i s i n s u f f i c i e n t water, plants and animals that cannot t o l e r a t e droughts may d i e , while i f there i s too much water, organisms may p e r i s h due to waterlogging or drowning. Factors that are not i n d i r e c t contact with the organism, and are thus no part of the d i r e c t environment, may a f f e c t those that are, e. g., fa c t o r s causing shading. These f a c t o r s are known as modifying f a c t o r s , and modify the environment.

Even i f one can d i v i d e the environment i n t o a number of c a t e g o r i e s , i t i s . extremely important to remember that the environment i s a vast complex of f a c t o r s which do not act separately but as a whole.

The Habitat

The habitat i s the space occupied by an organism containing the direct environmental factors at any particular time.

The term habitat may be employed i n a number of d i f f e r e n t ways. I t can be applied with respect to a s i n g l e organism or a group of the same species i n a p a r t i c u l a r l o c a t i o n . This i s sometimes c a l l e d the micro-h a b i t a t . A Species may occupy many d i f f e r i n g microhabitats depending on i t s tolerance to l i m i t i n g f a c t o r s . E. g., the p l a n t , Hebe striata or koromiko, which has a wide range of tolerance to l i m i t i n g f a c t o r s , can be found i n a v a r i e d range of microhabitats i n such widely d i f f e r i n g l o c a l i t i e s as tussock grasslands and c o a s t a l f o r e s t .

The combination of the t o t a l range of microhabitats c o n s t i t u t e s the macrohabitat f o r the organism. Hence koromiko has only one macro-ha b i t a t that incorporates a l l the c h a r a c t e r i s t i c s of i t s d i f f e r i n g micro­h a b i t a t s .

The term habitat may also be applied to a community (an aggregation of organisms characterised by i t s dominant s p e c i e s ) . A community of organisms, may be spoken of as l i v i n g i n a l e a f l i t t e r , s o i l or even f o r e s t h a b i t a t .

The Ecosystem

The Ecosystem is the functioning together of the community and the environment and forms the basic unit of ecology. It is the sum total of all the interactions between the environmental factors, animals and plants. For example a simple ecosystem may be a r o t t i n g l o g or, more complex, one region of f o r e s t .

One person's study i s u s u a l l y l i m i t e d to i s o l a t e d parts of the ecosystem, but the system as a whole may only be understood with the

- 3 -

synthesis of many such s t u d i e s . The concept of the ecosystem i s a broad one and should serve to emphasise the i n t r i c a t e r e l a t i o n s h i p s and i n t e r ­dependences that e x i s t w i t h i n i t .

THE ACTION OF SOME ENVIRONMENTAL FACTORS

Environmental f a c t o r s may be grouped under separate headings f o r convenience (see above), but such a c l a s s i f i c a t i o n has only l i m i t e d u s e f u l ­ness. To assess the a c t i o n and importance of these f a c t o r s with respect to the organism each f a c t o r must f i r s t be studied s i n g l y . This i s a necessary stage on the way to understanding the complexities of the environ­ment.

A number of examples have been sel e c t e d to show the e f f e c t and mode of a c t i o n of some of these f a c t o r s . I t must be r e a l i s e d that these separ­ate e f f e c t s are only part of a f a r greater and more complex system.

Of the c l i m a t i c f a c t o r s light i s a v i t a l and l i m i t i n g one, f o r without t h i s form of energy p l a n t s , the primary producers, would not be able to e x i s t and without these no other form of l i f e could s u r v i v e . In the t e r r e s t r i a l environment intensity and duration of l i g h t can be import­ant l i m i t i n g f a c t o r s , but t h i s i s not n e c e s s a r i l y so f o r the q u a l i t y (wave length). At high and low i n t e n s i t i e s l i g h t can r e s t r i c t the rate of photosynthesis l i m i t i n g growth and d i s t r i b u t i o n of plants and hence the d i s t r i b u t i o n of animals. The duration of l i g h t or day length i s now r e a l i s e d to be a major f a c t o r c o n t r o l l i n g the rhythms of organisms. For example i t has been shown that the reproductive cycles of both animals and plants are c o n t r o l l e d by day length.

Temperature, an e a s i l y measured f a c t o r , can l i m i t growth and d i s t r i b u ­t i o n of organisms and cause t h e i r zonation and s t r a t i f i c a t i o n . For example f r o s t tender species, (such as the New Zealand mangrove which w i l l not grow i n areas which have 4 degrees of f r o s t ) are confined to areas above t h e i r lower temperature l i m i t s .

Precipitation a f f e c t s the environment i n two ways. F i r s t l y i t det mines the humidity and thus the evaporating power of the a i r . The l a t t e r a f f e c t s the t r a n s p i r a t i o n of plants and dehydration i n animals. Secondly i t i s a source of available water (a resource), which i s a b a s i c necessity f o r l i f e . Water on the surface can be imbibed by animals while plants u t i l i s e s o i l water which also d i s s o l v e s and transports s o l u t e s .

The i n t e r a c t i o n of temperature and water is- a common one and shows how the e f f e c t of one f a c t o r may influence another. A v a i l a b l e water becomes scarce at extreme temperatures (deserts and a r c t i c r e g i o n s ) , while the e f f e c t of temperature i s greatest when there i s a d e f i c i t of water.

Gases c o n s t i t u t e another resource. Under normal conditions gases are not l i m i t i n g as they e x i s t i n constant proportions i n the atmosphere. However, i f the atmospheric e q u i l i b r i u m were disturbed n e i t h e r photo­synthesis or r e s p i r a t i o n could proceed e f f i c i e n t l y and t h i s would have a severe e f f e c t on growth of l i v i n g organisms.

- A -

Carbon dioxide and oxygen are u t i l i s e d by plants to manufacture n u t r i e n t s (e. g., sugars). These are combined with inorganic salts derived from the available sources i n the substratum to form a l l the classes of compounds found i n plant c e l l s . On the other hand animals derive t h e i r nutriment from the breakdown of n u t r i e n t compounds prev i o u s l y formed i n other organisms {food).

Besides organic compounds, inorganic compounds are also necessary to s u s t a i n l i f e , the most important being N, P, K, Ca, S, Mg. In a d d i t i o n small q u a n t i t i e s of Fe, Mn, Cu, Zn, B, Na, Mo, CI, V and Co, are e s s e n t i a l for healthy growth. With a l l the above fac t o r s i t i s the availability that i s important. I f s u i t a b l e nutriment i s not present, death or migration w i l l occur, while i f i t i s a v a i l a b l e i n i n s u f f i c i e n t q uantity growth d e f i c i e n c i e s w i l l r e s u l t .

Further environmental f a c t o r s , classed as resources, are substrate and shelter* Most trees and shrubs need a s t a b l e substratum to become e s t a b l i s h e d , and hence are not able to colonise many rocky h i l l s i d e s (an important f a c t o r i n the unstable New Zealand h i l l country). S h e l t e r i s a c r i t i c a l f a c t o r f o r animals when they are i n a defenceless stage of t h e i r l i f e c y c l e , e. g., young mammals and pupating i n s e c t s .

So f a r only p h y s i c a l ( a b i o t i c ) f a c t o r s have been discussed; these are u s u a l l y easy to measure and d e l i n e a t e , but i t must be emphasised that b i o t i c f a c t o r s are j u s t as important. The b i o t i c environment can be due to the presence and a c t i o n upon an organism of members of i t s own species or of members of other species. The e f f e c t of b i o t i c f a c t o r s can be negative, e. g., competition, or p o s i t i v e , e. g., aggregation and gregariousness. Competition must i n e v i t a b l y occur between members of the same species, as each member requires s i m i l a r environmental c o n d i t i o n s . When the population density i s such that competition becomes intense then only the i n d i v i d u a l s best s u i t e d f o r competition w i l l s u r v i v e . However both plants and animals can experience advantages by grouping together w i t h members of t h e i r own kind or with others. The aggregation of tussock plants i n t o clumps aids establishment and prevents i n d i v i d u a l s s u f f e r i n g from erosion, while the gregariousness of herd animals such as the Himalayan Thar affords some p r o t e c t i o n to the i n d i v i d u a l . Thus the population density of any species i s c o n t r o l l e d by the e q u i l i b r i u m between competition and aggregation.

Competition between members of d i f f e r e n t species i s demonstrated by the New Zealand Rata (Metrosideros robusta). By competing f o r l i g h t , space, n u t r i e n t s , e t c , i t eventually k i l l s the host p l a n t . Or the Shining Cuckoo, which deposits i t s eggs i n another b i r d ' s nest and as a n e s t l i n g competes f o r food and space with the young of other b i r d s .

Besides competition there are many va r i e d ways by which members of d i f f e r e n t species may i n t e r a c t :

1. Parasites may be a v i t a l f a c t o r l i m i t i n g the growth and d i s t r i b u t i o n of the host organism. The fungus Phytophthora cinamani. a serious patho­gen of many p l a n t s , e s p e c i a l l y Pinus radiata, can cause complete devastation

- 5 -

of whole stands of the host. The health of the Kiw i and of sheep and other introduced mammals s u f f e r s with heavy i n f e s t a t i o n s of t i c k s .

2. Symbiosis or Che l i v i n g together of two organisms to t h e i r mutual b e n e f i t , can be s i g n i f i c a n t i n the l i f e of many animals and p l a n t s . The l i c h e n , a combination of an alga and a fungus, i s a c l e a r example of t h i s . Rumen micro-organisms l i v i n g i n the caecum of cows and other herbivores, a s s i s t i n n u t r i t i o n , while the micro-organism receives s h e l t e r i n return. In both these cases the cooperation of each member i s e s s e n t i a l to the wellbeing of both.

3. Predation i s important to many small animals, an unless they have some form of p r o t e c t i o n , may r e s u l t i n t h e i r e l i m i n a t i o n from the area. Thus the population of small b i r d s and r a b b i t s can be severely a f f e c t e d by the depredations of hawks. Grazing (a form of predation) may l i k e w i s e deplete populations of e d i b l e plant species.

4. Another example i s oommensalism, where one organism derives b e n e f i t from another with n e g l i g i b l e e f f e c t on i t . The tuatara uses the burrows of p e t r e l s f o r s h e l t e r without s e r i o u s l y d i s r u p t i n g the l i f e of the p e t r e l , while epiphytes are another example, t y p i c a l of New Zealand vegetation.

Important environmental f a c t o r s not yet mentioned are those grouped under hazards. The e f f e c t of f l o o d s , f i r e , eruptions, e t c . are obvious and do not need to be elaborated.

The d i s c u s s i o n has included j u s t a few of the many and v a r i e d examples demonstrating the a c t i o n of i n d i v i d u a l environmental f a c t o r s . However i t must be r e a l i s e d that every organism i s subject to a complex of environment­a l f a c t o r s forming a r e a c t i o n system which contains the organism. This r e a c t i o n system includes the m o d i f i c a t i o n of the environment by the organism.

To show t h i s , an example of the a c t i o n of a known complex of environ­mental f a c t o r s can be seen i n the accompanying diagram. I t must be s t r e s s ­ed that i n nature a l l these f a c t o r s w i l l be i n t e r a c t i n g .

E c o l o g i c a l studies have an important economic value. Man can achieve a higher standard i n growth and health f o r h i s crops and f l o c k s by changing and modifying t h e i r environment. This i s t y p i f i e d i n New Zealand with the development of topdressing to re p l e n i s h n u t r i e n t s i n the s o i l s leading to good pasture and healthy l i v e s t o c k .

A s o p h i s t i c a t e d example of environmental m o d i f i c a t i o n i s that of b i o l o g i c a l c o n t r o l where pests may be regulated by the i n t r o d u c t i o n of b i o t i c f a c t o r s . This i s exemplified i n the measures taken to protect New Zealand's e x o t i c f o r e s t s against the depredations of Sirex noctilo, Sirex, a wood wasp, deposits i t s eggs i n holes d r i l l e d i n the tree by the female. Each egg i s i n f e c t e d by a fungus (Amylostereum) which causes white rot disease. This fungus predigests the timber f o r the l a r v a e , and renders the wood useless f o r production. Sirex was kept i n c o n t r o l by i t s n a t u r a l enemies i n i t s n a t i v e Europe, but i n New Zealand where i t had none, i t

SUN

Tha action of scrrw known environmental factors on an individual Kauri (Agathis australis).

- 7 -

spread r a p i d l y threatening the country's timber economy. In order to combat t h i s menace Rhyssa persuasoria was introduced. This wasp seeks out Sirex larvae with i t s long o v i p o s i t o r and lays her eggs which develop at the expense of the lar v a e . In t h i s way c o n t r o l of Sirex i s achieved.

However the i n d i s c r i m i n a t e i n t r o d u c t i o n of b i o t i c f a c t o r s may very r a p i d l y upset the f i n e balance of nature. A s t r i k i n g example was the uncontrolled devastation of manuka (Leptospermum scoparium manuka b l i g h t . Manuka, a pest to p a s t o r a l farmers, became known as a weed i n New Zealand. In 1942 i t was noticed that Eriococcus an introduced mealy bug attacked manuka and allowed i n f e c t i o n by Capnodium spp. a sooty mould fungus. The i n f e s t a t i o n was allowed to proceed u n t i l manuka was th r e a t ­ened with e x t i n c t i o n . However with the depletion of manuka there was a rapid increase i n erosion and subsequent damage to plant communities, which became a more serious threat than manuka i t s e l f . Later i t was noticed that another fungus (Myrangium spp. ) attacked the mealy bug and rendered i t innocuous, thus r e s t o r i n g the balance of nature.

Man by sound knowledge of ecology may, with care, c o n t r o l i n t e r ­actions between organisms and thus obtain a u s e f u l and potent force i n the m o d i f i c a t i o n of the environment. The future increase i n man's primary production w i l l depend on h i s a b i l i t y to manipulate the b i o t i c and a b i o t i c f a c t o r s of the environment.

Although t h i s a r t i c l e contains the minimum of concepts and examples the complexities of the environment have been c o n t i n u a l l y s t r e s s e d . The complex of i n t e r a c t i n g f a c t o r s must be observed and comprehended i n the f i e l d before an i n s i g h t can be gained i n t o the b i o l o g i c a l processes present i n nature.

REFERENCES

ALLAN, H. H, I960. New Zealand F l o r a . Govt. P r i n t e r .

BIELESKI, R. L. 1959. Factors a f f e c t i n g growth and d i s t r i b u t i o n of Kauri (Agathis a u s t r a l i s S a l i s b ) . Aust. Jour. Bot. 17, p. 252.

BRAUN-BLANQUET, J . 1932. Plant Sociology: the study of Pla n t Communities. Trans, by F u l l e r and Conrad. McGraw H i l l .

BROWNING, T. O. 1963. Animal Populations. Hutchinson & Co.

CARPENTER, J . R. 1938. An E c o l o g i c a l Glossary. Norman.

CHAPMAN, V. J . and RONALDSON. 1958. The Mangrove and S a l t Marsh F l a t s of the Auckland Isthmus. N. Z. D. S. I . R. B u l l . No. 125.

ENGLISH, D. A. 1965. M. Sc. Thesis ( i n preparation) Auck. Univ.

LITTLE, E. C. S. 1960. The Ecology of some New Zealand woody weeds, i n Biology of Weeds. Symp. No. l of B r i t . E c o l . Soc.

- 8 -

MAELZER, D. A. 1965. A discussion of Components of environment in Ecology. Jour. Theor. Biol. 8(1) p. 153.

MASON & LANGENHEIM. 1957. Language Analysis and the Concept of Environment. Ecology 38, p. 325.

McINTOSH, R. P. 1963. Ecosystems, Evolution and relational patterns of living organisms. Amerc. Sci. 51(2), p. 246.

MIRAMS, R. V. 1957. Aspects of the natural regeneration of the Kauri (Agathis australis). Trans. Roy. Soc. N. Z. 84(4), p. 661.

NEWHOOK, F. J. 1960. The Association of Phytophthora spp. with mortality of Pinus radiata and other conifers. N. Z. Jour. For. VIII(2), p. 266.

ODUM, E. P. 1959. Fundamentals of Ecology. Saunders.

COSTING, H. J. 1950. The study of Plant Communities, an introduction to Plant Ecology. Freeman.

PETERSON, P. J. 1960. Mineral Nutrition of Kauri Seedlings. M. Sc. Thesis Auck. Univ.

PLAIT, R. B. 1958. Ultimate subdivisions of the environment and species adjustment* Bull. of Georgia Acad. Sci. XVI, p. 84.

1960. Environment* Enc. of Sci. & Tech* McGraw H i l l .

POOLE, A. L. 1962. New Zealand Forestry. Govt. Printer*

ROACH, R. W. 1954* Observations on Kiwis from L i t t l e Barrier Is. Tane 6, p. 153.

YAPP, 1922. The concept of Habitat. Jour, of Ecol. 10, p. l .