T. Muotka et A. Penttinen, DETECTING SMALL-SCALE SPATIAL PATTERNS IN LOTIC PREDATOR-PREY RELATIONSHIPS - STATISTICAL-METHODS AND A CASE-STUDY, Canadian journal of fisheries and aquatic sciences, 51(10), 1994, pp. 2210-2218
We mapped the exact locations of two predaceous stream insects, a cadd
is larva (Rhyacophila obliterata) and a stonefly nymph (Isoperla gramm
atica), in 1-m(2) sampling windows in relation to their major prey, la
rval black flies (mostly Simulium sublacustre), which were quantified
within the same areas by extensive systematic sampling. In mid-June, w
hen black flies were abundant and highly clustered, R. obliterata was
also aggregated on a scale of 5-10 cm. After the emergence of black fl
ies in the beginning of July, the point pattern of the rhyacophilid wa
s random. Isoperla grammatica was abundant only on the earlier samplin
g occasion, at which time it was randomly distributed. We also analyse
d spatial association between the two predators and found a weak indic
ation of small-scale inhibition between them. In the range of current
speeds of 40-60 cm/s, microhabitat overlap between the caddisfly and b
lack fly was intensive, leading to high consumption of this semi-sessi
le prey. The second-order methods used proved powerful in detecting sm
all-scale spatial patterns and could be more widely used by ecologists
in place of classical single- statistic indices whenever detailed map
ping of individuals is feasible.