DOI: 10.5061/dryad.gf1vhhn3d
title: The competition-tolerance trade-off as a cause of species turnover along environmental gradients: The role of population differentiation

description: One of the latest advances in studying species distribution proposes that
 the universal occurrence of a trade-off between competition and
 environmental tolerance explains the segregated distribution of closely
 related species along environmental gradients. Given that this
 proposition applies to species that are closely related, here we moved one
 step down and explored the possibility that a trade-off between
 competition and tolerance also controls the distribution of populations
 within species that occupy different environments. We tested our
 hypothesis with populations of the annual herb Centaurea solstitialis that
 grow at low versus high elevation (hereafter, Mediterranean versus steppe
 populations, respectively) in Anatolia. We characterized climatic
 conditions in which these populations grow and conducted a common garden,
 where we measured traits predicted to affect environmental tolerance, and
 an intraspecific competition experiment, that included different
 densities, with Mediterranean and steppe populations. We found that
 Mediterranean populations experience climatic conditions that appear more
 favorable for early growth than those experienced by steppe populations.
 Specifically, conditions are warmer and wetter upon this species emergence
 in the Mediterranean than steppe region. In addition, Mediterranean
 populations exhibited trait attributes typically associated with benign
 environments, whereas steppe populations displayed attributes thought to
 cope with harsh environments. These attributes included smaller seeds,
 lower dormancy, faster emergence and seedling growth, and higher specific
 leaf area in Mediterranean than steppe populations. Finally, individuals
 from Mediterranean populations were stronger competitors than those from
 steppe populations. Together, these findings suggest that adaptation to
 harsh environments comes at the expense of competitive ability in our
 study populations, and that this compromise may control their separated
 distribution along elevational/climatic gradients. Population
 differentiation may thus precede the later observed turnover of related
 species along environmental gradients proposed to be caused by the
 competition-tolerance trade-off.
description: # The competition-tolerance trade-off as a cause of species turnover along
 environmental gradients: The role of population differentiation Dataset
 DOI: [10.5061/dryad.gf1vhhn3d](https://doi.org/10.5061/dryad.gf1vhhn3d) ##
 Description of the data and file structure Data are from two experiments
 conducted under common conditions in the greenhouse. ### Files and
 variables #### File:
 Length_of_longest_leaf_through_time_for_Anatolian_pops.csv
 **Description:** This file includes the length of the longest leaf at 30,
 60, and 105 days after emergence in our common garden experiment. #####
 Variables * Sampling (days): Days after seedling emergence on which leaf
 length was recorded. * Region: Region from where populations were
 collected; that is, Mediterranean or Steppe. * Population: Number given to
 study populations. * Individual: Number of the individual measured within
 each population. * Length longest leaf (cm):  Length of the longest leaf
 in cm. Empty cells respond to the fact that there was no individual to
 measure in pots. * rgr (cm day-1): Relative growth rate in cm per
 day. That is, the length of the leaf divided by 30, 60, or 105. Empty
 cells respond to the fact that there was no individual to measure in pots.
 #### File: Pappus_seed_mass_of_Anatolian_populations.csv
 **Description:** This file includes the mass of seeds with a pappus used
 in our common garden experiment. ##### Variables * Date: Weighing date. *
 Region: Region from where populations were collected; that is,
 Mediterranean or Steppe. * Pop#: Number given to study populations. *
 Ind#: Number of the individual measured within each population. * Pappus
 seed#: Number of the seed measured within each individual. * Pappus seed
 mass (g): Seed mass in grams. #### File:
 Precipitation_and_temperature_in_the_10_Mediterranean_and_10_steppe_sites_in_Anatolia.csv **Description:** This file has precipitation and temperature data of weather stations located near Mediterranean and steppe populations in our study. ##### Variables * Site: Name of the site where the weather station is located. * Latitude (N): Latitude coordinate where sites are located. * Longitude (E): Longitude coordinate where sites are located. * Elevation (m): Meters above sea level at which sites are located. * Month: Name of the month of the year. * Mean precipitation (kg/m2): Average precipitation for the given month across years in kilograms per meter square. * Mean temperature (ºC): Average temperature for a given month across years in Celsius degrees. #### File: SLA_of_Anatolian_populations.csv **Description:** File with data of specific leaf area (sla) of Anatolian populations in our common garden experiment. ##### Variables * Region: Region from where populations were collected; that is, Mediterranean or Steppe. * Population: Number given to study populations. * Individual: Number of the individual measured within each population. * Leaf weight (g): Dry weight in grams of the leaf used to calculate sla. * Leaf area (cm2): Area in square centimeters of the leaf used to calculate sla. * SLA: Specific leaf area (leaf area divided by leaf weight). #### File: RIIs_for_Anatolian_populations.csv **Description:** File with data of relative interaction indices (RIIs) of Anatolian populations in our competition experiment. ##### Variables * Pot: Pot number * Density: Number of plants per pot. * Ind within pot: Number of the individual measured within the pot. * Target: Origin of the individual measured within the pot. * Competitor: Origin of the individual serving as a competitor within the pot. * Pop: Name of the population included in the study. * Ind within pop: Number of the individual within a given population. * Dry weight (g): Dry weight of the aboveground biomass of seedlings in grams. This variable has empty cells for cases in which individuals were missing in the pot. * RII: Relative interaction index. This column has empty cells for density 1 and for cases where the target or the competitor was missing in the pot. #### File: Seedling_emergence_Anatolian_pops_for_257_days.csv **Description:** This file contains the data for seedling emergence in our common garden experiment.  ##### Variables * Region: Region from where populations were collected; that is, Mediterranean or Steppe. * Population: Number given to study populations. * Individual: Number of the individual measured within each population. * Seeds added to pots: Number of seeds added to pots. * D1 to D257: Days at which emergence within pots was recorded.  This variable has empty cells when no emergence was observed. * prop: This variable is repeated from D4 (first day after seeding with emergence in pots) to D257 (last day at which emergence was observed).  This variable is the proportion of seedlings that emerged at a give day (emerged seedling divided the number of seeds added to pots). * cum: This variable is repeated from D4 (first day after seeding with emergence in pots) to D257 (last day at which emergence was observed).  This variable is the cumulative proportional emergence for a given sampling day. * Timson: Timson’s index.  Column with empty cells for pots with no emergence. #### File: Germination_rate_of_Anatolian_pops_for_competition_experiment.csv **Description:** This file includes germination data of populations used in the competition experiment of our study.  Specifically, they are linked to the following sentence in our manuscript: “Seeds were pre-germinated at room temperature on one Whatman paper (#3) placed inside plastic dishes (9 cm diameter) watered with 10 mL distilled water [n=3 dishes (one per individual) with 20 seeds per dish]**.**  Seed germination was used to estimate germination rate for 15 days (Timson’s index).” ##### Variables * Region: Region from where populations were collected; that is, Mediterranean or Steppe. * Population:  Number given to study populations. * Dish: Replicate the number of the dish where seeds were germinated.  Values go from 1 to 3. * Seeds added to dishes: Number of seeds placed within each dish for germination. * 1-15: Days at which germination was recorded. * Prop1-15: Proportion of seeds germinated at each sampling day from day 1 to day 15.  Sampling was conducted on days 1, 2, 3, 4, 5, 6, 7, 9, 11, 13, and 15. * Cum1-10: Cumulative germination proportion for each sampling day. * Timson: Timson’s index.