Cockroache; Ecology, behavior & history - W.J. Bell

ecological significance in deserts and other extreme environments
because it allows for decomposition during periods
when it would not normally occur—in times of
drought or excessive heat or cold (Ghabbour et al., 1977;
Taylor and Crawford, 1982; Crawford and Taylor, 1984).
Significance of Cockroaches as Decomposers
The importance of plant litter decomposers to soil formation
is unquestioned (Odum and Biever, 1984; Vitousek
and Sanford, 1986; Whitford, 1986; Swift and Anderson,
1989; Meadows, 1991). Soils in turn provide an
array of ecosystem services that are so fundamental to life
that their total value could only be expressed as infinite
(Daily et al., 1997). Detailing the contribution of cockroaches
relative to other decomposers, however, is difficult.
First, information is scarce. For any given ecosystem,
it is the decomposers that receive the least detailed
attention. Second, like most decomposers, cockroaches
are so adaptable that they often do not have well defined
ecological roles; functional redundancy among detritivores
is high (Scheu and Setälä, 2002). Third, because of
the intricate synergistic and antagonistic interactions
among diverse bacteria, fungi, and invertebrates, decomposition
is manifested in scales of space and time not easily
observed or quantified. Decomposition occurs both
internal and external to the gut, and at microscopic spatial
scales. It operates via the creation of physical artifacts,
like burrows and fecal pellets, which accumulate and continue
to function in the absence of their creators. Effects
can be localized and short term, or wide ranging and extended
in time; wood decomposition in particular is a
very long-term stabilizing force in forest ecosystems (Anderson
et al., 1982; Anderson, 1983; Swift and Anderson,
1989; Wolters and Ekschmitt, 1997; Wardle, 2002).
Other problems in attempting to quantify the role of
arthropods in decompositional processes are related to
sampling bias; no one method works best for all groups
and all soils (Wolters and Ekschmitt, 1997). The results of
pitfall trapping, for example, can be difficult to interpret.
No cockroaches were taken in unbaited pitfall traps in
four habitats in Tennessee, but traps attracted quite a
number of blattellids when bait (cornmeal, cantaloupe,
fish) was added (Walker, 1957). Surface-collecting methodology
such as soil and litter cores may not account for
cockroach species that are only active after seasonal precipitation
or those that shelter under bark, under stones,
or in other concealed locations during the day. Sampling
techniques for canopy arthropods also have methodological
biases with regard to a given taxon, particularly those
species in suspended soils and those that are seasonally
present. Diurnal, seasonal, and spatial aggregation further
complicate the proper estimation of abundance
(Basset, 2001).
Members of the blattoid stem group undoubtedly
played a major role in plant decomposition during the
Paleozoic (Shear and Kukalová-Peck, 1990). The ecological
significance of extant cockroaches, however, is usually
assumed to be negligible (Kevan, 1993) because of their
often low numbers during surveys (e.g., some Australian
studies—Postle, 1985; Tanton et al., 1985; Greenslade and
Greenslade, 1989). If considered in terms of biomass,
however, their importance is magnified because of large
individual body size relative to many other detritivores
such as mites and Collembola. Basset (2001), in a review
of studies conducted worldwide, concluded that cockroaches
dominated in canopies, comprising an astonishing
24.3% of the invertebrate biomass (discussed in
Chapter 3). The clumped distribution and social tendencies
of many species also tends to increase their ecological
impact. Cockroaches that aggregate in tree hollows,
for example, directly benefit their host plant, as defecation
steadily fertilizes the soil at the base of the tree
(Janzen, 1976). Large, subsocial or gregarious woodfeeding
cockroaches may be able to pulverize logs on a
time scale comparable to, if not better than, termites. In
this regard, several studies in montane environments report
that cockroach population levels in plant litter are
negatively correlated with the presence of termites, a
group that strongly and predominantly influences the
pattern of decomposition processes and whose ecological
importance is clear. Surveys on Mt. Mulu in Sarawak,
Borneo, indicate that the density of soil- and litterdwelling
termites declines with altitude (Collins, 1980).
Cockroaches were present in low numbers at all altitudes,
but individuals were larger and more numerous in upper
montane forests, where they constituted 40% of the total
macrofauna biomass. Rhabdoblatta was the most common
genus at upper altitudes, found in all plots from
1130 m upward, but not below. The Cryptocercus punctulatus
species complex dominates the saproxylic guild in
the Southern Appalachian Mountains, and occupies the
same niche as does the subterranean termite Reticulitermes
at lower elevations (Nalepa et al., 2002). The same
altitudinal trend was evident in soil and litter core samples
taken on Volcán Barva in Costa Rica; the biomass of
cockroaches fluctuated, but generally increased with altitude.
Termites were not found above 1500 m, but cockroaches
made up 61% of the biomass at that altitude
(Atkin and Proctor, 1988). On Gunung Silam, a small
mountain in Sabah, the altitudinal associations were reversed.
At 280 m, cockroaches were 84% of the invertebrate
biomass and termites were not found; at 870 m, termites
were 25% of the biomass, while cockroaches were
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