188
#. WALOFF
birds is typically S-shaped (Fig. €9, aa is general of vertebrate p d f o r s
(Holling, 1961).
Flocks of Blue Tits were usually observed in the b m m Area 4 in
spring, and Agwu (1967) recorded that birds preyed on caterpillars of
Lewptera. In the spring the 1arv.ae moult into their final instar and the
mines then bulge and become conspicuous. It is at this stage that
Leucqtera suffers considerable mortality from birds which slit open the
mines and remove the larvae. The density of the bulging mines was
greatest in 1966 and it was then that bird preda,tion was particularly
intense.
E. UENERAL CONSIDERATIONS
Broom is a plant which grows readily on disturbed soils and for this
remon stands of bushes of fairly uniform age are not uncommon. The
growing bushes become rapidly colonised by the broom fauna and as
populatims of phytophagous insects develop they form focal points in
the hunting grounds of predators. We have seen such a development of
prey and predator populations in the broom plantation in Area 4. The
assemblage of arthropod predators on broom is large (Table LII) and
they are particularly effective because moat of them are only facultative.
Only a few species living in the sheltered microhabitats of broom pods,
stem mines, or root nodules, temporarily escape the onslaught of the
predacious arthropods.
As broom bushes grow, characteristic litter accumulates under them.
This provides shelter for many predators, especially in the winter
months. Earwigs frequently hibernate in the curled-up dehisced pods
on the bushes, or in litter, so does Anthocoris sarothmni and the highly
predacious mite Anystis baccarum. In this connection, it is interesting
that even in the severe winter of 1962-63, temperature in the broom
litter never fell below 0.5' (Danthanarayana, 1965).
Most predatory species feed on any available prey, but some show a
degree of selectivity. Thus two species of anthocorids feed preferentially
on psyllids. The closest relationship is established by Anthocork 8umthmni and the Psyllidae on broom, but both the predator and the prey
are confined to the same host plant. Again, syrphid larvae feed on
aphids and the behaviour of the ovipositing adults appears adapted to
that end. Blue Tits select alatae and the larger aphids, while Miridm
feed on prey of small size, for instance the early instars of their kin.
In specialised microhabitats new predators appear; within the broom
pod larvae of Lestodiplosis feed on those of Clidipbsi.8, while the wood
boring beetles are preyed on by the larvae and adults of Limophhus
ater which lives within their mines.
Immediate (functional) responses of predators to increase of prey
#. WALOFF
birds is typically S-shaped (Fig. €9, aa is general of vertebrate p d f o r s
(Holling, 1961).
Flocks of Blue Tits were usually observed in the b m m Area 4 in
spring, and Agwu (1967) recorded that birds preyed on caterpillars of
Lewptera. In the spring the 1arv.ae moult into their final instar and the
mines then bulge and become conspicuous. It is at this stage that
Leucqtera suffers considerable mortality from birds which slit open the
mines and remove the larvae. The density of the bulging mines was
greatest in 1966 and it was then that bird preda,tion was particularly
intense.
E. UENERAL CONSIDERATIONS
Broom is a plant which grows readily on disturbed soils and for this
remon stands of bushes of fairly uniform age are not uncommon. The
growing bushes become rapidly colonised by the broom fauna and as
populatims of phytophagous insects develop they form focal points in
the hunting grounds of predators. We have seen such a development of
prey and predator populations in the broom plantation in Area 4. The
assemblage of arthropod predators on broom is large (Table LII) and
they are particularly effective because moat of them are only facultative.
Only a few species living in the sheltered microhabitats of broom pods,
stem mines, or root nodules, temporarily escape the onslaught of the
predacious arthropods.
As broom bushes grow, characteristic litter accumulates under them.
This provides shelter for many predators, especially in the winter
months. Earwigs frequently hibernate in the curled-up dehisced pods
on the bushes, or in litter, so does Anthocoris sarothmni and the highly
predacious mite Anystis baccarum. In this connection, it is interesting
that even in the severe winter of 1962-63, temperature in the broom
litter never fell below 0.5' (Danthanarayana, 1965).
Most predatory species feed on any available prey, but some show a
degree of selectivity. Thus two species of anthocorids feed preferentially
on psyllids. The closest relationship is established by Anthocork 8umthmni and the Psyllidae on broom, but both the predator and the prey
are confined to the same host plant. Again, syrphid larvae feed on
aphids and the behaviour of the ovipositing adults appears adapted to
that end. Blue Tits select alatae and the larger aphids, while Miridm
feed on prey of small size, for instance the early instars of their kin.
In specialised microhabitats new predators appear; within the broom
pod larvae of Lestodiplosis feed on those of Clidipbsi.8, while the wood
boring beetles are preyed on by the larvae and adults of Limophhus
ater which lives within their mines.
Immediate (functional) responses of predators to increase of prey