174
N. WdUlFp
Dempster (1966) obtained a very rough measure of total nymphal
mortality by subtracting the peak of adult numbers from that of the
nymphs. He then subtracted the average nymphal mortality due to
parasitism and obtained a residue of unexplained mortality including
that due to predation (Table L). The pattern shown by this residual
mortality, which must be mainly due to predators, is supported by the
resulta of the precipitin test, where mortality due to predation was
lowest in Heterocordylua and highest in 0. oirescens. Heter0Cordydu.s does
not have to contend with predation by other miride, while 0. virescens
has Heterocwdylus, Asciodema and 0. ademcarpi feeding on it. These
t h e e predatory species are greatly reduced in number by the time
0. concolot is present, while 0. viregeens ie probably not predatory on
other species.
TABLE L
Thc average ex-tent of u n a p h i d mo~&~Zity for each qecie.9 for
the yews 1959-65 (Dempster, 1966)
Average
Averege
Average
nYmPhd
due to
mortality,
mortality
paresitiam
including
predation
%
%
%
Heterooodyha
76.6
56.4
20.2
totel
mortality
unexpleined
Ai?Cbd&W
81.8
58.1
23.7
0. a d e w v .
46.7
10-5
36.2
0.oircsccne
.
63.7
22.8
40.9
0. concolor
43 *O
ia.6
24.4
E. THE COEXISTENCE OF FIVE BPEOIES OB YIRIDAE
ON BROOM
The subject of coexistence of ecological homologues and of congeneric species has been recently discussed by DeBach (1966) and by
Williams (1964). DeBach defines an ecological homologue as “two or
more different species having the same ecological niche . . .” and says
that an ecological niche ‘(refers to the role pltlyed by an animal based
upon its food, spatial or habitudinal requirements in a particular habitat”. The co-existence of congeneric species in the same habitat appears
to be a very common phenomenon in insects and Williams’ statistical
investigation (1964) shows that in nearly every case examined there
are more congeneric species and fewer genera than would be expected
by chance. He concluded by saying that either the conception that
N. WdUlFp
Dempster (1966) obtained a very rough measure of total nymphal
mortality by subtracting the peak of adult numbers from that of the
nymphs. He then subtracted the average nymphal mortality due to
parasitism and obtained a residue of unexplained mortality including
that due to predation (Table L). The pattern shown by this residual
mortality, which must be mainly due to predators, is supported by the
resulta of the precipitin test, where mortality due to predation was
lowest in Heterocordylua and highest in 0. oirescens. Heter0Cordydu.s does
not have to contend with predation by other miride, while 0. virescens
has Heterocwdylus, Asciodema and 0. ademcarpi feeding on it. These
t h e e predatory species are greatly reduced in number by the time
0. concolot is present, while 0. viregeens ie probably not predatory on
other species.
TABLE L
Thc average ex-tent of u n a p h i d mo~&~Zity for each qecie.9 for
the yews 1959-65 (Dempster, 1966)
Average
Averege
Average
nYmPhd
due to
mortality,
mortality
paresitiam
including
predation
%
%
%
Heterooodyha
76.6
56.4
20.2
totel
mortality
unexpleined
Ai?Cbd&W
81.8
58.1
23.7
0. a d e w v .
46.7
10-5
36.2
0.oircsccne
.
63.7
22.8
40.9
0. concolor
43 *O
ia.6
24.4
E. THE COEXISTENCE OF FIVE BPEOIES OB YIRIDAE
ON BROOM
The subject of coexistence of ecological homologues and of congeneric species has been recently discussed by DeBach (1966) and by
Williams (1964). DeBach defines an ecological homologue as “two or
more different species having the same ecological niche . . .” and says
that an ecological niche ‘(refers to the role pltlyed by an animal based
upon its food, spatial or habitudinal requirements in a particular habitat”. The co-existence of congeneric species in the same habitat appears
to be a very common phenomenon in insects and Williams’ statistical
investigation (1964) shows that in nearly every case examined there
are more congeneric species and fewer genera than would be expected
by chance. He concluded by saying that either the conception that