10.5061/DRYAD.12JM63Z1G
Xing, Shuang
0000-0001-5956-6904
Sun Yat-sen University
Distribution of ant assemblage, microclimate and microhabitat along
vertical gradients
Dryad
dataset
2022
FOS: Biological sciences
Czech Science Foundation
http://dx.doi.org/10.13039/501100001824
21-06446S
en
https://doi.org/10.22541/au.164873567.76113604
27650 bytes
3
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Abiotic and biotic factors structure species assembly in ecosystems both
horizontally and vertically. However, the way community composition
changes along comparable horizontal and vertical distances in complex
three-dimensional habitats, and the factors driving these patterns,
remains poorly understood. By sampling ant assemblages at comparable
vertical and horizontal spatial scales in a tropical rain forest, we
tested hypotheses that predicted differences in vertical and horizontal
turnover explained by different drivers in vertical and horizontal space.
These drivers included environmental filtering, such as microclimate
(temperature, humidity, and photosynthetic photon flux density) and
microhabitat connectivity (leaf area) which are structured differently
across vertical and horizontal space. We found that both ant abundance and
richness decreased significantly with increasing vertical height. Although
dissimilarity between ant assemblages increased with vertical distance,
indicating a clear distance-decay pattern, the dissimilarity was higher
horizontally where it appeared independent of distance. The pronounced
horizontal and vertical structuring of ant assemblages across short
distances is likely explained by a combination of microclimate and
microhabitat connectivity. Our results demonstrate the importance of
considering three-dimensional spatial variation in local assemblages and
reveal how highly diverse communities can be supported by complex
habitats.
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. 2). 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 at 1 m
above the ground (Fig. 2). 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. In
total, we obtained and identified ant assemblage samples for 61 out of 86
sampling points, with 14 samples having no ants, nine samples having been
lost between sampling and analysis, and two samples in Transect 5 (two
individual ants discovered) belonging to an emergent forest layer without
horizontal positions for comparison. To quantify microclimate and habitat
structure, air temperature (˚C) and relative humidity (%) were measured at
0.5 h intervals over 24 hours using Hobo Pro RH/Temperature Data Logger
(Onset Computer Corporation, Pocassest, MA, USA). Data loggers were placed
at 3 m intervals along each vertical transect, starting 1 m above the
ground. At the data logger locations, photosynthetic photon flux density
(PPFD) was recorded using a handheld light meter (Quantum Lightmeter,
Spectrum Technologies, Plainfield, 1L, USA) and normalized by dividing by
maximum light value within each vertical transect to account for
between-day variation in lighting. The intent was to identify the relative
(not absolute) light environment of the forest canopy (Dial et al 2006).
We estimated one-sided total leaf area between sampling trays as a measure
of microhabitat connectivity at different sampling points for transects 1
to 6 (T1-T6; Fig 2c). The leaf area within a sampling interval was
calculated by multiplying the number of leaf intersections by the size of
the base area of the interval which was 1 m2 (the area of the sample
tray). We then used these data to estimate leaf area index (LAI) over
vertical intervals (sampling methods described in Dial et al. 2004, 2006,
and 2011; estimation methods in Dial et al. 2006 and 2011). Conceptually,
LAI refers to the number of leaf layers above the ground surface that
would be pierced by a vertical line. For example, if LAI = 7, then there
are, on average seven leaf layers above a random point on the ground
within that height range; or 7 m2 of leaf area per m2 of ground surface.
We assumed (following MacArthur and Horn 1969) that for any sample point
in the canopy located at height z above the ground, the foliage density
was approximately equal in all directions. Following this assumption at
each height z, we systematically measured horizontal distances (di) with a
laser range finder to the nearest canopy element (foliage and stems) in 12
uniformly distributed azimuths every 2 m vertically from the ground to the
height of the horizontal traverse line supporting the vertical transect.
Using the n ≤ 12 distances to foliage at each sample point, we found the
mean distance (d) to foliage, doubled the mean (assuming that the observer
was on the average midway between foliage elements), then inverted it to
find leaf intersections per vertical meter at height z as LAIz = 1/(2d).
By multiplying the LAIz by collection area (1m2) we estimated the leaf
area sampled within the interval.