126
nae, can be used very effectively against smaller enemies and frequently enables individuals to escape from
attacks.
Besides these direct mechanical defenses, certain
behaviors tend to minimize the possibility of contact
with enemies. I observed in anostracans, specifically
Dendrocephalus, that individuals are always found in
those parts of their temporary habitats which are free
of submerged vegetation. In most cases, these are the
central and often deeper parts, where the absence of
vegetation reduces the possibility of attacks by hidden
predators or enemies searching within the vegetation
for prey.
Conchostracans, in contrast, perhaps with the
exception of the very early developmental stages, frequently avoid free-swimming movements. They often
attach to or hide within the vegetation or at the bottom of the ponds. The very young do not hide in
the vegetation, but they stop swimming movements
when they contact an object in the water and begin
to sink inactively for a certain time and so possibly
could move out of danger. As conchostracan communities become older, these free-swimming movements
become scarcer.
The strategy of contacting submerged vegetation
and hiding is highly developed by Cyclestheria hislopi.
This form can be found year-round in permanent waters
and in the presence of very effective predators, such as
planktivorous fish. I found C. hislopi enclosed within a
special mucus capsule hidden within submerged vegetation or at the bottom of the margins of shallow ponds.
Cyclestheria also develop directly, both from parthenogenetic eggs within the maternal brood chamber and
from latent eggs enclosed in a strong ephippium. Thus
they avoid the vulnerable free-swimming early developmental stages and, when the young larvae leave the
protective maternal carapace, they start at once to form
a mucus capsule.
Nevertheless, with the exception of Cyclestheria,
and in spite of these behavioral mechanisms, sooner or
later conchostracan populations become extinct when
confronted with enemies. This process often occurs
very fast. I observed the total extermination of large
populations of Eulimnadia by invading coleopterans
within one or two days in small ponds. In Colombia,
conchostracan populations are frequently exterminated before their temporary habitats dry out, so they
generally have an effective ecological life expectancy
that is considerably shorter than their physiological life
expectancy.
To complete these considerations on adaptation to
temporary waters, I should note the apparent restriction of populations to the early phases of ecological
successions. Doubtlessly, most of the cysts hatch soon
after rainfalls. Some others do not hatch immediately
but remain as a reserve, waiting for a future opportunity after a new drying of their habitat (Roessler,
1989, 1990; Roessler, unpublished data). Nevertheless, I observed that after an initial peak, hatching of
resting eggs continues, although at a very low rate. This
was also shown in cultures for Eulimnadia antlei by
Belk (1972). Thus conchostracan larvae can be found
in very low numbers in otherwise advanced phases
of community development especially in somewhat
larger ponds, and at moderated temperatures. Occasionally, these larvae develop to sexual maturity and
may reproduce, especially in larger or deeper (generally cooler) ponds, with dense submerged vegetation.
In these circumstances, I have sometimes found very
large specimens in advanced states of development.
These specimens obviously did not undergo infraspecific stress and high temperature, and are among the
largest individuals I captured. One must deduce from
this example that notwithstanding the clearly recognizable adaptations to temporary waters, conchostracans
may persist into the later stages of community succession in temporary waters.
Distribution patterns
In addressing the distribution patterns of Colombian
conchostracans, I will take into account their special
adaptation to the particular characteristics of temporary freshwater bodies. Within any region, species differ in their adaptations to temporary habitats. There
is also infraspecific and interspecific competition and
overlapping of ecological niches among species.
The Colombian conchostracan fauna includes 12
species, in five families. All species are restricted to the
tropical lowlands (I never found conchostracans above
1300 m). Thus, all Colombian species are typical warm
water forms. Only a few species have a widespread
distribution and can be found in the lowlands throughout the country; most seem to be restricted to specific
regions.
Cyclestheriidae
Cyclestheria hislopi (Baird, 1859) is a very frequent
species, which has been reported as a circumtropical
nae, can be used very effectively against smaller enemies and frequently enables individuals to escape from
attacks.
Besides these direct mechanical defenses, certain
behaviors tend to minimize the possibility of contact
with enemies. I observed in anostracans, specifically
Dendrocephalus, that individuals are always found in
those parts of their temporary habitats which are free
of submerged vegetation. In most cases, these are the
central and often deeper parts, where the absence of
vegetation reduces the possibility of attacks by hidden
predators or enemies searching within the vegetation
for prey.
Conchostracans, in contrast, perhaps with the
exception of the very early developmental stages, frequently avoid free-swimming movements. They often
attach to or hide within the vegetation or at the bottom of the ponds. The very young do not hide in
the vegetation, but they stop swimming movements
when they contact an object in the water and begin
to sink inactively for a certain time and so possibly
could move out of danger. As conchostracan communities become older, these free-swimming movements
become scarcer.
The strategy of contacting submerged vegetation
and hiding is highly developed by Cyclestheria hislopi.
This form can be found year-round in permanent waters
and in the presence of very effective predators, such as
planktivorous fish. I found C. hislopi enclosed within a
special mucus capsule hidden within submerged vegetation or at the bottom of the margins of shallow ponds.
Cyclestheria also develop directly, both from parthenogenetic eggs within the maternal brood chamber and
from latent eggs enclosed in a strong ephippium. Thus
they avoid the vulnerable free-swimming early developmental stages and, when the young larvae leave the
protective maternal carapace, they start at once to form
a mucus capsule.
Nevertheless, with the exception of Cyclestheria,
and in spite of these behavioral mechanisms, sooner or
later conchostracan populations become extinct when
confronted with enemies. This process often occurs
very fast. I observed the total extermination of large
populations of Eulimnadia by invading coleopterans
within one or two days in small ponds. In Colombia,
conchostracan populations are frequently exterminated before their temporary habitats dry out, so they
generally have an effective ecological life expectancy
that is considerably shorter than their physiological life
expectancy.
To complete these considerations on adaptation to
temporary waters, I should note the apparent restriction of populations to the early phases of ecological
successions. Doubtlessly, most of the cysts hatch soon
after rainfalls. Some others do not hatch immediately
but remain as a reserve, waiting for a future opportunity after a new drying of their habitat (Roessler,
1989, 1990; Roessler, unpublished data). Nevertheless, I observed that after an initial peak, hatching of
resting eggs continues, although at a very low rate. This
was also shown in cultures for Eulimnadia antlei by
Belk (1972). Thus conchostracan larvae can be found
in very low numbers in otherwise advanced phases
of community development especially in somewhat
larger ponds, and at moderated temperatures. Occasionally, these larvae develop to sexual maturity and
may reproduce, especially in larger or deeper (generally cooler) ponds, with dense submerged vegetation.
In these circumstances, I have sometimes found very
large specimens in advanced states of development.
These specimens obviously did not undergo infraspecific stress and high temperature, and are among the
largest individuals I captured. One must deduce from
this example that notwithstanding the clearly recognizable adaptations to temporary waters, conchostracans
may persist into the later stages of community succession in temporary waters.
Distribution patterns
In addressing the distribution patterns of Colombian
conchostracans, I will take into account their special
adaptation to the particular characteristics of temporary freshwater bodies. Within any region, species differ in their adaptations to temporary habitats. There
is also infraspecific and interspecific competition and
overlapping of ecological niches among species.
The Colombian conchostracan fauna includes 12
species, in five families. All species are restricted to the
tropical lowlands (I never found conchostracans above
1300 m). Thus, all Colombian species are typical warm
water forms. Only a few species have a widespread
distribution and can be found in the lowlands throughout the country; most seem to be restricted to specific
regions.
Cyclestheriidae
Cyclestheria hislopi (Baird, 1859) is a very frequent
species, which has been reported as a circumtropical