DOI: 10.5061/dryad.p2ngf1vxz
title: Urbanization drives partner switching and loss of mutualism in an ant-plant symbiosis

description: Mutualistic interactions between species underpin biodiversity and
 ecosystem function, but may be lost when partners respond differently to
 abiotic conditions. Except for a few prominent examples, effects of global
 anthropogenic change on mutualisms are poorly understood. Here we assess
 the effects of urbanization on a symbiosis in which the plant Cordia
 nodosa houses ants in hollow structures (domatia) in exchange for defense
 against herbivores. We expected to find that mutualist ants would be
 replaced in the city by heat-tolerant opportunists, leaving urban plants
 vulnerable to herbivory. In five protected forest sites and five urban
 forest fragments in southeast Perú, we recorded the identity and heat
 tolerance (CTmax) of ant residents of C. nodosa. We also assayed their
 plant-defensive behaviors and their effects on herbivory. We characterized
 the urban heat-island effect in ambient temperatures and within domatia.
 Forest plants housed a consistent ant community dominated by three
 specialized plant-ants, whereas urban plants housed a suite of ten
 opportunistic taxa that were, collectively, about 13 times less likely
 than forest ants to respond defensively to plant disturbance. In the
 forest, ant exclusion had the expected effect of increasing herbivory, but
 in urban sites, exclusion reduced herbivory. Despite poor ant defense in
 urban sites, we detected no difference in total standing herbivory,
 perhaps because herbivores themselves also declined in the city. Urban
 sites were warmer than forest sites (daily maxima in urban domatia
 averaged 1.6°C hotter), and the urban ant community as a whole was
 slightly more heat tolerant. These results illustrate a case of mutualism
 loss associated with anthropogenic disturbance. If urbanization is
 representative of increasing anthropogenic stressors more broadly, we
 might expect to see destabilization of myrmecophytic mutualisms in forest
 ecosystems in the future.
description: Methods are detailed in the main manuscript.
description: # Urbanization drives partner switching and mutualism breakdown in an
 ant-plant symbiosis This
 dataset includes eight files that document differences between urban and
 forest sites in the symbiotic interaction between Cordia nodosa plants and
 ants that live within the plants' domatia. Files are listed below,
 along with a description of the data included in each column. ##
 Description of the data and file structure | file name | column header |
 explanation | | :---------------------- |
 :--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | hobo.csv | | dataset of ambient temperatures collected with hobo pendant data loggers 1.5 m above ground in Cordia nodosa plants; loggers were shaded, not shielded. Data from site 'Aeropuerto' were visualized but not analyzed statistically.  | | | date\_time | date and time of temperature reading YYYY-MM-DDTHH:MM:SSZ | | | site | name of site where logger was placed | | | tempC | temperature in degrees celsius | | | site\_type | b = forest, u = urban | | thermocouple.csv | dataset of domatia temperatures collected with thermocouple data loggers inside Cordia nodosa domatia | | | | date\_time | date and time of temperature reading MM/DD/YYYY HH:MM | | | site | name of site where logger was placed | | | plant | ID of individual plant where logger was placed | | | tempC | temperature in degrees celsius | | | type | b = forest, u = urban | | plantinfo.csv | for focal plants used in the disturbance experiment - information about plant size (number of domatia) and canopy cover | | | | site | name of site | | | type | b = forest, u = urban | | | date | date data were recorded | | | plant | ID of individual plant | | | domatia | number of domatia on plant | | | canopy\_density | canopy density (percent) | | ant\_community.csv | for all 68 plants with specimen-based ant identifications, this sheet lists ant identities and site-taxon CTmax values | | | | type | b = forest, u = urban | | | site | name of site | | | plant | ID of individual plant | | | actual\_ant | ant taxon found in domatia. Lines where 'actual\_ant' = 'no\_ants' were used in analysis of ant presence/absence, but excluded from CTmax and community analyses. | | | ctmax\_site | CTmax for that ant taxon at that site (see "ctmax.csv" for individual measurements) | | | excl | exclude row from analysis of community-level CTmax: y = yes, n = no, m = maybe (for alternative versions of analysis). Note ctmax\_site = NA was also excluded independently of this column. | | | expl | if 'excl' = 'y' or 'm', this column explains why | | behavior.csv | results of behavioral assay; a domatium was flicked and ant response recorded; assay repeated on 2 domatia per plant, morning and afternoon | | | | date | date of assay | | | time | time of assay (am = morning, pm = afternoon) | | | site | name of site | | | type | b = forest, u = urban | | | plant | ID of individual plant | | | ants\_pre | number of ants present on leaves associated with focal domatium prior to disturbance | | | response\_time\_s | number of seconds elapsed from disturbance until ants left domatia and patrolled plant at a higher level than before; 60 was maximum time allotted and indicates no response | | | response\_cat | 0 = no response (or ants stopped foraging and hid inside domatia), 1 = defensive response | | | actual\_ant | ant taxon found in the assayed plant. NA means ants were present during the assay but were not field identifiable and could not be found for a voucher at the end of the day after assays were complete | | exclusion.csv | results of 10-day ant exclusion experiment in May 2022. Two leaves were selected per domatium, one had ants excluded with tanglefoot on the petiole, and the other was left as a control | | | | site | name of site | | | type | b = forest, u = urban | | | plant | ID of individual plant | | | actual\_ant | ant taxon found in the assayed plant | | | trt | C = control, E = exclusion | | | new\_herbiv | 0 = no new chewing herbivory during the 10 days, 1 = new chewing herbivory present on leaf; assessed by direct comparison of before and after photos of individual leaves to identify new damage | | | new\_herbiv\_cm2 | area in square cm of new chewing herbivory incurred during the 10 day experiment, measured using imageJ software | | | new\_herbiv\_on\_pair | 0 = none, 1 = new herbivory present on at least one leaf in the pair (i.e., the experimental portion of the plant was 'discovered' by herbivores) | | ctmax.csv | results of CTmax assays | | | | vial\_ID | unique ID for individual ant | | | control | c = control ant (not exposed to heat); NA = ant subjected to CTmax assay | | | control\_lived | y = control lived with no impairment to mobility, posture, righting response; n = control died or was impaired, NA = not a control ant | | | CTmax | in degrees C, the heat-block temperature at which ant lost muscular control | | | date | date of CTmax assay (M/DD/YYYY) | | | start\_time | assay start time (HH:MM:SS) | | | actual\_ant | ant taxon | | | site | name of site of origin where ant was collected | | | plant | ID of individual plant where ant was collected | | | type | b = forest, u = urban | | | date\_coll | date ant was collected in the field (M/DD/YYYY) | | | time\_coll | time ant was collected in the field (HH:MM:SS) | | standing\_herbivory.csv | herbivory measurements in December 2022 | | | | site | name of site | | | type | b = forest, u = urban | | | plantID | ID of individual plant; does not correspond to plants studied in May 2022 | | | age | subjectively assigned leaf age, j = young, m = mature, v = old | | | leaf | leaf replicate, nested within age nested within plantID | | | herbiv\_prop | proportion of leaf area missing due to chewing herbivory, measured in LeafByte app |