DOI: 10.5061/dryad.4mw6m909j
title: Rates of premature fruit drop for 201 plant species on Barro Colorado Island, Panama

description: Pre-dispersal seed mortality caused by premature fruit drop is a
 potentially important source of plant mortality, but one which has rarely
 been studied in the context of tropical forest plants. Of particular
 interest is premature fruit drop triggered by enemies, which – if
 density-dependent – could contribute to species co-existence in tropical
 forest plant communities.  We used a long-term (31 year) dataset
 on seed and fruit fall obtained through weekly collections from a network
 of seed traps in a lowland tropical forest (Barro Colorado Island, Panama)
 to estimate the proportion of seeds prematurely abscised for 201 woody
 plant species. To determine whether enemy attack might contribute to
 premature fruit drop we tested whether plant species abscise more of their
 fruit prematurely if they: (1) have attributes hypothesised to be
 associated with high levels of enemy attack, and (2) are known to be
 attacked by one enemy-group (insect seed predators). We also tested (3)
 whether mean rates of premature fruit drop for plant species are
 phylogenetically conserved. Overall rates of premature fruit drop were
 high in the plant community. Across all species, 39% of seeds were
 abscised before completing their development. Rates of premature seed
 abscission varied considerably among species and could not be explained by
 phylogeny. Premature seed abscission rates were higher in species which
 are known to host pre-dispersal insect seed predators and species with
 attributes that were hypothesised to make them more susceptible to attack
 by pre-dispersal enemies, namely species which (1) have larger seeds, (2)
 have a greater average height, (3) have temporally predictable fruiting
 patterns, and (4) are more abundant at the study site. Synthesis.
 Premature fruit drop is likely to be a major source of seed mortality for
 many plant species on Barro Colorado Island. It is plausible that
 pre-dispersal seed enemies, such as insect seed predators, contribute to
 community-level patterns of premature fruit drop and have the potential to
 mediate species co-existence through stabilising negative density
 dependence. Our study suggests that the role of pre-dispersal enemies in
 structuring tropical plant communities should be considered alongside the
 more commonly studied post-dispersal seed and seedling enemies.
description: <strong>Description of methods used for
 collection/generation of data</strong> Since
 1987, weekly censuses of seed rain have been conducted within the 50-ha
 plot as part of a research project coordinated by S. J. Wright. A first
 set of seed traps (n = 200) was established in 1987 and has been
 continuously monitored since then. These seed traps are located at 13.5 m
 intervals on alternating sides of and 4-10 m from 2.7 km of pre-existing
 trails within the 50-ha plot. Another 50 traps were added in naturally
 occurring tree fall gaps within the 50-ha plot between 2002 and 2004 and
 have been monitored since. A final set of 200 traps were established 2 m
 from each of the 200 original traps in 2011 and were censused for 23
 months. Each trap consists of a 0.8 m tall PVC frame and 1 mm mesh
 covering 0.5 m2 of forest floor. In weekly censuses, all fruits and seeds
 encountered in each trap are identified to species, counted, and
 categorised as mature or immature. In some species, late flowers included
 flowers with swollen ovules. These late flowers were categorised
 separately and excluded from this study. Fruits labelled as ‘immature’
 were dropped several weeks to months later. The distinction between
 immature and mature fruits was based on the examination of endocarps: If
 the endocarp of seeds within a fruit is filled with material that is solid
 (rather than hollow or filled with liquid or soft substances), the fruit
 was considered mature. Our species-specific estimates of rates of
 premature seed abscission are based on the relative frequencies of mature
 and immature fruits. Since we did not conduct systematic germination
 trials across the full range of species, we cannot rule out the
 possibility that some of the seeds scored as immature would be able to
 germinate. We are still confident that in the vast majority of cases, the
 seeds inside fruits scored as immature are indeed inviable (given the
 timing at which the bulk of premature fruit drop happens in many species)
 and that premature fruit drop typically translates to seed mortality in
 the studied plant community.  <strong>Methods for
 processing the data</strong> In this study, we
 used information on fruits and seeds from woody plant species (trees,
 shrubs, and lianas) recorded in the traps during the period 1988 to 2018
 (31 full calendar years). All analyses and data preparation were conducted
 in R v 4.0.5. Counts of fruit in the traps were multiplied by
 species-specific average seed-to-fruit ratios (S. J. Wright; unpublished
 data) and added to the number of seeds. For each species, the weekly
 counts (n = 1615 censuses) of mature and immature seeds were then summed
 across all seed traps. This was done separately for each full calendar
 year in the dataset. Since 90% of species fruit only once during a
 calendar year, and since few species fruit in the December-January period,
 this approach will typically generate data on overall fruit drop rates for
 individual fruiting events. Not all species were encountered in every
 single year, but in total there were 5,295 unique species × year
 combinations in the original dataset. Only species × year combinations
 with fewer than 10 fruits or individual seeds were analysed for the
 publication. Species names were matched to a static copy of The World
 Flora Online (http://www.worldfloraonline.org) v.2021.01 valid at
 2021-12-09 using the function "WFO.match" from the R package
 {WorldFlora}. The function "WFO.one" was then used to find one
 unique matching name for each submitted name. using the argument
 'priority = "Accepted"', it first limits candidates to
 accepted names, with a possible second step of eliminating accepted names
 that are synonyms. Note that the species with the 4-letter ID code GUA1 is
 listed as a synonym of <em>Guarea guidonia</em> in The World
 Flora Online database. This is incorrect. The former <em>Guarea
 grandifolia</em> (GUA1) and <em>Guarea guidonia</em>
 (GUA2) are distinct species. Pennington (1981) provided the name
 <em>Guarea megantha</em> for GUA1, which we adopt
 here.
description: <strong>fruit_drop.csv</strong>
 Number of variables: 11 Number of cases/rows:
 5295 Variable List:  year Calendar year for which the data was collected sp4 4-letter ID code of plant species. This code does not change and can be used to track earlier botanical names to compare across publications. family Plant family genus Plant genus species Plant species infraspecific_epithet The scientific name for any taxon below the rank of species. The majority of species in this dataset do not have an infraspecific epithet, entries for these species are recorded as "NA". abscised_seeds Count of prematurely abscised seeds summed across seed traps. Count of prematurely abscised seeds was estimated as the number of immature fruits found in the traps multiplied by species-specific seed-to-fruit ratios. viable_seeds Count of viable seeds summed across seed traps. Count of viable seeds was estimated as the number of mature fruits found in the traps multiplied by species-specific seed-to-fruit ratios, plus the number of single diaspores found in the traps. total_seeds abscised_seeds + viable_seeds proportion_abscised abscised_seeds / total_seeds sum_parts Count of reproductive organs or parts (number of fruits + number of single diaspores)