tudinal zones: lowland (0-800 m), intermediate (800-
2000 m), and montane (2000+ m). In undisturbed ar-
eas, these zones are usually distinct, but deforestation
may allow some dry lowland species to become more
widespread at higher altitudes. Lowland species oc-
cur widely, from the Nicaraguan to the Panamanian
border, but no species extends from the lowlands to
the summits of the highest mountains. Geographical
range generally decreases with increasing altitude;
endemism is greatest at high altitudes. Cloud forest
hymenopteran faunas reflect their position as inter-
mediate between lowlands and high altitudes. The
following discussion is based on six years of Malaise
trap samples taken at Zurqui de Moravia (Hanson and
Gauld 1995; Fig. 4.12).
Taxa that are less diverse in cloud forests than in lowland
forests. Many Hymenoptera either are restricted to
lower elevations or are more speciose in the lowlands
than in cloud forests (Fig. 4.14). Nest-building species
and their associates (parasitoids and cleptoparasites)
are one such group. Pompilids, vespids, sphecids, and
bees occur at high elevations, although they are rep-
resented by few species, but ants are largely absent
above 2400 m. The lower diversity of nest-building
hymenopterans at higher altitudes may be a conse-
quence of lack of a sustained period of temperature
suitable for foraging. In high-altitude sites, sharp di-
urnal temperature fluctuations, coupled with frequent
cloud cover, severely reduce foraging times. Climate
unpredictability may have more severe consequences
for nest-building species than parasitoids, as the lat-
ter can more easily take advantage of short periods of
favorable weather while the former must attend to a
nest for at least several consecutive days. Although
species richness decline occurs with increasing lati-
tude, groups such as ants are present in northern tem-
perate areas where climates are harsher than tropical
mountaintops. However, temperate and boreal regions
have a predictable short continuous period during
which daily temperatures permit foraging and colony
growth. An exception to this general pattern of alti-
tudinal and latitudinal decline in species richness are
the bumblebees, which overcome temperature restric-
tions by thermoregulating with their vibrating tho-
racic muscles (Heinrich 1979).
Parasitoids and cleptoparasites of nest-building
hymenopterans also decrease in species richness with
increasing altitude. Examples include Trigonalyiidae
(parasitoids of social wasps), Gasteruptiidae (clepto-
parasites of solitary wasps and bees), diapriids (Procto-
trupoidea) associated with ants, Eucharitidae (para-
sitoids of ants), some ichneumonids, Chrysididae
(subfamily Chrysidinae, parasitoids and/or clepto-
parasites of solitary wasps and bees), Mutillidae (para-
sitoids of solitary wasps and bees), and cleptoparasitic
genera of pompilids, sphecids, and bees.
Another group that decreases in species richness
with altitude are nocturnally active species. Low night-
time temperatures at higher altitudes may severely
restrict their activity. Few nocturnal hymenopterans
fly later than 2200 hr in the mountains (I. Gauld, un-
publ. data). Examples include Ophioninae, Netelia
(Ichneumonidae), and many Rogadinae (Braconidae).
The largest genus of Ophioninae, Enicospilus, is rep-
resented by about 50 species in Santa Rosa National
Park (0—300 m), about 30 species in the greater Monte-
verde area, and only three species above 2000 m
(Gauld 1988).
Parasitoids of wood-boring beetles also decrease in
species richness with altitude. Some are completely
absent from cloud forests: Orussidae, Stephanidae,
Aulacidae, and Phasganophorini (Chalcididae). Other
groups, although present in cloud forests, are repre-sea- 200 400 600 800 10001200140016001800200022002400260028003000
level mmmmmmmmmmmmmmmFigure 4.14. The number of species of Anomaloninae occurring at different altitudes in
Costa Rica.127 Insects and Spiders