STUDIES ON THE INSECT FAUNA ON SCOTCH BROOM
197
and can be used in considering the speciea living on Sarothamnue 8wpariwr. Geier (1966) said “in a life system, neither populations nor
environments are taken aa entitiee in their own right, but as constituent
elements of the system”. The ooncept ia not a new one and reeembles
that of an “ecosystem”, but I find it 8 very convenient one in thinking
about the complex of species on broom, aa it unifies the habitat provided by a shrub growing in a tempemte climate with its fauna of
phytophagous speciea, their constellations of pertusitea and the more
diffuse assembly of predators. The life system is a dynamic one, since
the plant is relatively short lived and the resources provided by it are
continually changing (Waloff, 1968).
Broom bushes rarely live for more than 10-16 years and their initial
rapid growth in the fbt 4-6 years is succeeded by 2-3 years of relative
stability which ia followed by degeneration accompanied by increase
in the ratio of wood to green material, reduction in seed production and
finally death (see Section 11). Bushes rarely die in one year, but as the
habitat begins to disintegrate, a mosaic of dead, partly dead and Living
plants is formed. The fauna concentrates on the living parts and may
suffer increased predation, aa we have found in our studies on
Phytdeda.
Broom often oolonises disturbed soils and then the stands of bushes
tend to be of a fairly uniform age. Thus, both in plantations and in
many self-sown plote of broom, the eventa tend to be cyclical, not only
in the plltnt itself, but also in the fauna that livea on it.
Seedlings and young bushes are colonised rapidly and most of the
common insect species arrive in the first two yeam As yet, we know
very little about the attractive qualities of this host plant and much
remains to be found out. Smith (1966b) experimented with Sparteine,
an alkaloid in broom which may aid host aelection, at least for the aphid
Acyrthmiphon and Makings (1966) pointed out that the choice of the
oviposition sites by the moth, Chesiae kgateUa waa reinforced by the
odour of broom.
The bushes and the insect populations on them grow and expand
simultaneously, but it seems probable that within the life span of any
area of broomland of more or less uniform age, many of the species will
reach a single peak of abundance, after which their numbers decline.
This limitation is imposed on the fauna by the relatively short life of
the host plant and consequently by the local reduction in the size of
the habitat, accompanied by its slow regeneration. Thus in 12 years
(1948-5,9), the population of Phytdectu reached a single peak of abundance in 1960 and finally declined together with the habitat. Similarly
in Area 4, broom waa plslnted in 1967 rsnd the population of the five
species of Miridae reached their peaks of abundance in 3 Lo 6 generations
197
and can be used in considering the speciea living on Sarothamnue 8wpariwr. Geier (1966) said “in a life system, neither populations nor
environments are taken aa entitiee in their own right, but as constituent
elements of the system”. The ooncept ia not a new one and reeembles
that of an “ecosystem”, but I find it 8 very convenient one in thinking
about the complex of species on broom, aa it unifies the habitat provided by a shrub growing in a tempemte climate with its fauna of
phytophagous speciea, their constellations of pertusitea and the more
diffuse assembly of predators. The life system is a dynamic one, since
the plant is relatively short lived and the resources provided by it are
continually changing (Waloff, 1968).
Broom bushes rarely live for more than 10-16 years and their initial
rapid growth in the fbt 4-6 years is succeeded by 2-3 years of relative
stability which ia followed by degeneration accompanied by increase
in the ratio of wood to green material, reduction in seed production and
finally death (see Section 11). Bushes rarely die in one year, but as the
habitat begins to disintegrate, a mosaic of dead, partly dead and Living
plants is formed. The fauna concentrates on the living parts and may
suffer increased predation, aa we have found in our studies on
Phytdeda.
Broom often oolonises disturbed soils and then the stands of bushes
tend to be of a fairly uniform age. Thus, both in plantations and in
many self-sown plote of broom, the eventa tend to be cyclical, not only
in the plltnt itself, but also in the fauna that livea on it.
Seedlings and young bushes are colonised rapidly and most of the
common insect species arrive in the first two yeam As yet, we know
very little about the attractive qualities of this host plant and much
remains to be found out. Smith (1966b) experimented with Sparteine,
an alkaloid in broom which may aid host aelection, at least for the aphid
Acyrthmiphon and Makings (1966) pointed out that the choice of the
oviposition sites by the moth, Chesiae kgateUa waa reinforced by the
odour of broom.
The bushes and the insect populations on them grow and expand
simultaneously, but it seems probable that within the life span of any
area of broomland of more or less uniform age, many of the species will
reach a single peak of abundance, after which their numbers decline.
This limitation is imposed on the fauna by the relatively short life of
the host plant and consequently by the local reduction in the size of
the habitat, accompanied by its slow regeneration. Thus in 12 years
(1948-5,9), the population of Phytdectu reached a single peak of abundance in 1960 and finally declined together with the habitat. Similarly
in Area 4, broom waa plslnted in 1967 rsnd the population of the five
species of Miridae reached their peaks of abundance in 3 Lo 6 generations