DOI: 10.5061/dryad.73n5tb2x2
title: Stem boring and ant occupation of six Brazilian Cerrado trees

description: Wood-boring beetle larvae act as ecosystem engineers by creating stem
 cavities that are used secondarily as nests by many arboreal ant species.
 Understanding the heterogeneity and distribution of available cavities and
 their use by ants is therefore key to understanding arboreal ant community
 assembly and diversity. Our goals were to quantify the abundance and
 diversity of beetle-produced cavity resources in a tropical canopy, reveal
 how ants use these resources, and determine which characteristics of the
 cavity resource contribute to ant use. We dissected branches from six
 common tree species in the Brazilian Cerrado savanna, measuring cavity
 characteristics and identifying the occupants. We sampled 2,310 individual
 cavities, 576 of which were used as nests by 25 arboreal ant species. We
 found significant differences among tree species in the proportion of stem
 length bored by beetles, the number of cavities per stem length, average
 entrance hole size, and the distribution of cavity volumes. The likelihood
 that a cavity was occupied was greater for cavities with larger entrance
 hole sizes and larger volumes. In particular, there was a strong positive
 correlation between mean head diameters of ant species and the mean
 entrance hole diameter of the cavities occupied by those ant species.
 Wood-boring beetles contribute to the structuring of the Cerrado ant
 community by differentially attacking the available tree species. In so
 doing, the beetles provide a wide range of entrance hole sizes which ant
 species partition based on their body size, and large volume cavities that
 ants appear to prefer.
description: This study focused on six Cerrado tree species which are
 characteristic of Cerrado vegetation in general, and are abundant in our
 study site: <i>Caryocar brasiliense </i>(Caryocaraceae),
 <i>Stryphnodendron polyphyllum </i>(Fabaceae), <i>Qualea
 grandiflora </i>(Vochysiaceae), <i>Kielmeyera coriacea
 </i>(Calophyllaceae), <i>Machaerium opacum
 </i>(Fabaceae), and <i>Tachigali aurea
 </i>(formerly<i> Sclerolobium aureum,</i> Fabaceae). In
 June-August 2012 (“small stem” dataset) and June-August 2013 (“large stem”
 dataset), we sampled branches from 90 individual trees occurring in mid to
 low-canopy density savanna vegetation (cerrado <i>sensu
 stricto</i>). All trees were growing at least 15 m from conspecifics
 and except for two trees of the large data set, were 40 m from any trail.
 All were sufficiently tall, i.e., 6-10 m in height, to comprise part of
 the tree canopy. Together, trees sampled for the small and large data sets
 were distributed across approximately 1 km<sup>2</sup> and 2.1
 km<sup>2</sup>, respectively. For the large
 stem dataset, we removed a single 10-cm diameter branch with all attached
 biomass from 12 individuals of each tree species. To minimize impact on
 trees, only large trees with three or more 10-cm diameter branches were
 sampled. Because of the growth form and availability of
 <i>Stryphnodendron polyphyllum</i>, branches sampled from this
 species ranged from 7.5-10 cm at the base (samples from only two
 individuals were under 9.0 cm). From an additional six individuals for
 each tree species (the small stem dataset), we sampled between six and
 fifteen 3-cm diameter branches, with more branches sampled from larger
 trees. Bole diameters were measured 10 cm above the soil level using
 digital calipers. Trees often branch below breast height in Cerrado,
 preventing the more common measurement of diameter at breast height. The
 10-cm diameter branches and all attached stems greater than 3 cm diameter
 were cut using a chainsaw at 10-cm intervals and split lengthwise to
 expose any cavities. We measured both the xylem diameter at the basal end
 of each 10-cm length and the total length of cavities encountered. When
 present, we measured entrance-hole diameter, taking multiple measurements
 for non-circular shapes and averaging for analysis. Cavity diameter was
 measured at 10-cm intervals along the length of the cavity and then
 averaged for analyses. Cavity inhabitants were identified in the field,
 taking voucher specimens to the lab for confirmation when necessary.
 Because of the scarcity of dead stems of larger diameter, all stems from
 this dataset were living wood. For the small stem
 dataset, stems (3 cm diameter and under) were measured for total length
 and basal xylem diameter, and then split lengthwise to expose cavities.
 Measurements were taken on all cavities encountered, including occupant
 species, cavity length, minimum and maximum diameter, and diameter of any
 entrance holes. We also recorded whether the cavities in these small stems
 were located in live or dead wood. Voucher specimens of
 ants found in stems were collected for identification. Ant specimens were
 identified to species or morphospecies using our existing expertise in the
 system and vouchers deposited at the Zoological Collection at the
 Universidade Federal de Uberlândia, in Brazil. Vouchers were deposited in
 this same collection. Measurements of ant head width were made with a
 stereoscopic microscope with a zoom lens and a built-in micrometer,
 measured to the nearest tenth of a millimeter. Sample size ranged from one
 individual per species for rare species up to 85 individuals from as many
 as 32 different trees, with never more than five individuals per
 tree.
description: There are 4 data sets. 1. Ant body size:
 average body size of ant species encountered in cavities.
 2. Characteristics and inhabitants of cavities found in small
 stems (&lt; 3 cm diameter) for the 6 tree species. Each data line is a
 different cavity. 3. Characteristics and inhabitants of
 cavities found in small stems (&gt; 3 cm diameter) for the 6 tree
 species. Each data line is a different cavity. 4.
 Summary of measures by tree for both large and small stem data
 sets. All measurements are in cm except for ant body
 size measurements, which are in mm. When data are
 "missing" for ants and other invertebrates, no organisms were
 found in those cavities. The diameter measure for a
 cavity is the diameter of the cavity measured from one inside surface to
 the opposite inside surface. A wood diameter measure for a cavity is the
 diameter of the cavity plus the wood on the outside, i.e., the full
 diameter of the stem at the point of measurement.