2.2 Field sampling
The field survey consisted of several activities. First, we established
the vertical sampling system in April 2002 via a 200 m long application
of “canopy trekking” to access the forest trees to secure the
horizontal traverse line (Dial et al. 2004a). Once the 130 m traverse
line was secured near the top of the three tallest trees, each
> 65 m above ground level, we suspended seven vertical
transects (Fig. 1). We used these vertical transects to sample the
canopy interior systematically from 1 m above ground to the traverse
line 55-65 m above ground. Finally, we collected instantaneous measures
of photosynthetically active radiation with a handheld meter,
temperature and humidity with suspended data logging sensors, and
fogging samples in May 2002 (Dial et al. 2006).
Ant assemblages
Ant assemblages were sampled using insecticide fogging between 0700 and
0930 on 12-24 May 2002 from within the canopy by a climber rappelling
down using a Swing-Fog model SN50 (Phoenix Fogger, Dallas, TX, USA) near
each of seven vertical sample transects. These vertical transects were
suspended from a 130 m horizontal traverse line secured in the upper
canopy and were arranged at 20-25 m intervals horizontally (Fig. 1).
Each of these transects supported multiple individual circular fogging
trays (1 m2) (n=86) suspended in the air with attached
ethanol-filled collecting bottles spaced at approximately 5 m vertical
intervals beginning 1 m above ground (Fig. 1). These trays collected
knocked-down arthropods that were between trays at the time of fogging.
A 1.6% aqueous solution of the synthetic pyrethrum (Cypermethrin) was
used. Arthropods were collected into 80% ethanol 1-2 hours after
fogging, and ants were separated as part of arthropod ordinal sorting
(see Dial et al. 2006 for results on ordinal arthropod assemblages). The
ants sampled using fogging are mainly diurnal foraging species active
during the sampling period (0700 to 0930), and therefore likely present
a subset of the total local ant diversity.
All worker ants were identified to genus following Fayle et al (2014),
with relevant updates for taxonomy changes (Ward et al. 2015, Borowiec,
2016, Ward et al. 2016), and then separated into morphospecies. Where
possible, species names were assigned using online image databases
(www.antweb.org, www.antbase.net), published literature (Hung 1970,
Dorow and Kohout 1995, Schödl 1998, Kohout, 2006a, 2006b) and the
collections of TMF. Reproductive individuals were excluded from the
data, since their presence does not indicate an established colony,
mating flights can confound estimates of abundance, and they can be
challenging to match with workers unless entire nest series are
collected. Lone major workers were also excluded for the latter reason.
In total, we obtained and
identified ant assemblage samples for 63 out of 86 sampling points with
14 samples having no ants and 9 samples having been lost between
sampling and analysis. While all sample trays were suspended in the air
at systematic, standardized horizontal and vertical positions, some
trays captured no worker ants because there was only empty space with no
foliage or stems between the sample tray without worker ants and the
next sample tray above.