1. Spatial partitioning is a classic hypothesis to explain plant species coexistence, but evidenc... more 1. Spatial partitioning is a classic hypothesis to explain plant species coexistence, but evidence linking local environmental variation to spatial sorting, demography, and species' traits is sparse. If co-occurring species' performance is optimized differently along environmental gradients because of trait variation, then spatial variation might facilitate coexistence. 2. We used a system of four naturally co-occurring species of Clarkia (Onagraceae) to ask if distribution patchiness corresponds to variation in two environmental variables that contribute to hydrological variation. We then reciprocally sowed Clarkia into each patch type and measured demographic rates in the absence of congeneric competition. Species sorted in patches along one or both gradients, and in three of the four species, germination rate in the "home" patch was higher than all other patches. 3. Spatially variable germination resulted in the same three species exhibiting the highest populati...
Dataset (Data File Name: Datafile_Site_Herbivory.csv) describes the level of herbivory on plants ... more Dataset (Data File Name: Datafile_Site_Herbivory.csv) describes the level of herbivory on plants from populations that were part of the long-term demography study of Clarkia xantiana xantiana in Kern Co., CA from 2001-2015. Fruit production and fruits damaged on individual plants from 26 sites across years 2001 - 2015 (sites differ in number of years for which data have been collected).
The datafile (Data File Name: “Datafile_Survivorship_Fecundity.csv) contains data for long-tern s... more The datafile (Data File Name: “Datafile_Survivorship_Fecundity.csv) contains data for long-tern study of the demography of Clarkia xantiana xantiana in Kern Co., CA for 20 populations from 2006 to 2017. The dataset includes data on survivorship and fecundity of plants in permanent plots that were followed from germination to fruiting. At each site, 30 permanent plots of 0.5 m2 were established in 2006 along 4-6 transects. Each year, the number of seedlings in each permanent plot was recorded in February, the number of surviving fruiting plants and the average number of fruits per plant in each plot with fruiting plants were recorded in June. In 2006, only a subset of permanent plots were monitored for seedling germination, and fruit number per fruiting plant was not recorded. From 2006-2012, fruit number per plant was scored as the sum of undamaged fruits plus the “undamaged fruit equivalents” of damaged fruit. For example, if a plant had 2 damaged fruits, where half of each fruit w...
Datafile (Data File Name: “Datafile_Seed_Number_per_Fruit.csv) contains data on the number of see... more Datafile (Data File Name: “Datafile_Seed_Number_per_Fruit.csv) contains data on the number of seeds per fruit for long-term demographic study of Clarkia xantiana xantiana from 2006 to 2017. At each site, in each year, the number of fruits was counted on up to 150 plants per population. From 2006 to 2012, only undamaged fruit were collected. From 2013 to 2016, up to 30 undamaged and 30 damaged fruits were collected from separate plants.
Datafile (Data File Name: “Datafile_Fruiting_Plant_Density.csv) describes the fruiting plant numb... more Datafile (Data File Name: “Datafile_Fruiting_Plant_Density.csv) describes the fruiting plant number in quadrats followed on permanent transects for long-term demographic study of Clarkia xantiana xantiana from 2006 to 2017. At each site, in each year, fruiting plant number was counted in between 30 and 150 0.5 m2 quadrats distributed haphazardly throughout site. The number of quadrats depends on the areal extent of the population. For the 20 populations included in the detailed demography studies, data from 30 permanent plots are included.
The dataset (Data File Name: “Datafile_Fruit_Number_per_Plant.csv”) describes the fruit productio... more The dataset (Data File Name: “Datafile_Fruit_Number_per_Plant.csv”) describes the fruit production per plant for up to 150 plants for each of the 35 populations followed in a long-term demographic study of Clarkia xantiana xantiana in Ker Co., CA. At each site, in each year, the number of fruits per plant was recorded on up to 150 plants per population. From 2006-2012, fruit number per plant was scored as the sum of undamaged fruits plus the “undamaged fruit equivalents” of damaged fruit. For example, if a plant had 2 damaged fruits, where half of each fruit was missing, the number of undamaged fruit equivalents was scored as 1, and added to the number of undamaged fruits. From 2013-2017, undamaged and damaged fruits were scored separately.
Site locations and environmental variables of 35 populations of Clarkia xantiana ssp. xantiana wh... more Site locations and environmental variables of 35 populations of Clarkia xantiana ssp. xantiana where plant density and fruit production have been measured in a long term demographic study. The datafile (Data File Name: Datafile_Site_Environment.csv) details the full names of the sites, locality information, lat/long locations, slope, elevation, soil parent material, and radiation factors. The README file describes all of the column names in detail.
Darwin’s theory of natural selection successfully explains why organisms are designed to meet env... more Darwin’s theory of natural selection successfully explains why organisms are designed to meet environmental challenges, his simple proposal being that heritable traits that confer survival benefits on individuals will come to predominate in populations (Darwin 1859). Thus, it was a special challenge for him to explain the evolution of secondary sex characters that impair survival in animals. His proposed solution was the theory of sexual selection, according to which features that enhance mating success can evolve despite a possible survival cost (Darwin 1871). This original concept and its recent refinements (see reviews in Andersson 1994; M∅ller 1994; Andersson and Iwasa 1996) were inspired by obvious patterns. For example, it is easy to distinguish female and male peafowl by sight at a great distance, and the males’ exaggerated tails clearly appear to hinder locomotion and camouflage.
The immediate capacity for adaptation under current environmental conditions is directly proporti... more The immediate capacity for adaptation under current environmental conditions is directly proportional to the additive genetic variance for fitness, VA(W). Mean fitness, W, is predicted to change at the rate (VA(W))/W, according to Fishers Fundamental Theorem of Natural Selection. Despite ample research evaluating degree of local adaptation, direct assessment of VA(W) and the capacity for ongoing adaptation is exceedingly rare. We estimated VA(W) and total lifetime fitness in three pedigreed populations of the annual Chamaecrista fasciculata, over three consecutive years in the wild. Contrasting with prevailing expectations of minimal VA(W), we found significant VA(W) in all populations and years, predicting increased mean fitness (0.83 to 6.12 seeds per individual). Further, we identified two instances predicting evolutionary rescue, where selection on standing VA(W) was expected to increase fitness of declining populations (W < 1.0) to levels consistent with population sustainab...
The co-occurrence of several dimensions of resource separation between coexisting consumers stren... more The co-occurrence of several dimensions of resource separation between coexisting consumers strengthens the hypothesis that the separation arose from and/or ameliorates interspecific competition. The two most common pollinators of the California endemic plant Clarkia xantiana ssp. xantiana (Onagraceae), the bees Hesperapis regularis (Mellitidae) and Lasioglossum pullilabre (Halictidae), are known to partition flower resources by flower colour. Here we asked whether H. regularis and L. pullilabre also partition flower resources by diurnal foraging schedule and by food type (pollen versus nectar). We also quantified diurnal patterns of nectar availability, expected to be related to foraging schedules and forager responses to flower colour. The diurnal schedules of the two species differed distinctly and significantly. The majority of L. pullilabre foraging visits occurred before midday, while the majority of H. regularis visits occurred afterwards. The two species foraged for alternat...
ABSTRACT Background/Question/Methods Whether closely related species can coexist is expected to d... more ABSTRACT Background/Question/Methods Whether closely related species can coexist is expected to depend on their evolutionary divergence in niches, relative to their evolutionary divergence in competitive ability. Also critical is the spatial scale at which niche differences appear. Even if close relatives exhibit strongly conserved environmental responses at large geographic scales, they may be able to coexist if their niches differ sufficiently at smaller (i.e., within-community) scales where neighborhood competition and population processes play out. To characterize the spatial scales at which niche differences appear between close relatives, we carried out hierarchical spatial analysis of environmental variation, distribution, and performance in the California-endemic annual plants Clarkia xantiana ssp. xantiana and C. speciosa ssp. polyantha, which have broadly overlapping geographic ranges and sometimes co-occur on smaller scales. Results/Conclusions At the scale of their entire ranges, the distributions of the two species are determined very similarly by variation in climate but differ somewhat in their associations with topography and soils, C. speciosa ssp. polyantha’s presence being associated with shallower slopes, more southerly aspects, and a broader range of substrates. More distinct species-presence associations with topography and substrate appeared at the scale of hundreds of meters, a pattern mirrored by species differences in relationships between abundance, reproductive performance, topography, and soil texture at scales of meters to tens of meters. At the neighborhood scale (centimeters to decimeters), however, individual distribution and performance (water status and biomass) and were spatially structured but not detectably associated with environmental variation. We hypothesize that species differences in plant-soil relations across many scales underlie some degree of spatial separation and allow species coexistence, despite strong similarity in climatic niche, while stochastic processes play a larger role in individual distribution at the smallest scales.
While the idea that water stress contributes to geographic range limits in arid-land plants is we... more While the idea that water stress contributes to geographic range limits in arid-land plants is well founded, it remains to be determined how environmental sources of water stress help determine—along with other environmental, demographic, and evolutionary genetic ...
1. Spatial partitioning is a classic hypothesis to explain plant species coexistence, but evidenc... more 1. Spatial partitioning is a classic hypothesis to explain plant species coexistence, but evidence linking local environmental variation to spatial sorting, demography, and species' traits is sparse. If co-occurring species' performance is optimized differently along environmental gradients because of trait variation, then spatial variation might facilitate coexistence. 2. We used a system of four naturally co-occurring species of Clarkia (Onagraceae) to ask if distribution patchiness corresponds to variation in two environmental variables that contribute to hydrological variation. We then reciprocally sowed Clarkia into each patch type and measured demographic rates in the absence of congeneric competition. Species sorted in patches along one or both gradients, and in three of the four species, germination rate in the "home" patch was higher than all other patches. 3. Spatially variable germination resulted in the same three species exhibiting the highest populati...
Dataset (Data File Name: Datafile_Site_Herbivory.csv) describes the level of herbivory on plants ... more Dataset (Data File Name: Datafile_Site_Herbivory.csv) describes the level of herbivory on plants from populations that were part of the long-term demography study of Clarkia xantiana xantiana in Kern Co., CA from 2001-2015. Fruit production and fruits damaged on individual plants from 26 sites across years 2001 - 2015 (sites differ in number of years for which data have been collected).
The datafile (Data File Name: “Datafile_Survivorship_Fecundity.csv) contains data for long-tern s... more The datafile (Data File Name: “Datafile_Survivorship_Fecundity.csv) contains data for long-tern study of the demography of Clarkia xantiana xantiana in Kern Co., CA for 20 populations from 2006 to 2017. The dataset includes data on survivorship and fecundity of plants in permanent plots that were followed from germination to fruiting. At each site, 30 permanent plots of 0.5 m2 were established in 2006 along 4-6 transects. Each year, the number of seedlings in each permanent plot was recorded in February, the number of surviving fruiting plants and the average number of fruits per plant in each plot with fruiting plants were recorded in June. In 2006, only a subset of permanent plots were monitored for seedling germination, and fruit number per fruiting plant was not recorded. From 2006-2012, fruit number per plant was scored as the sum of undamaged fruits plus the “undamaged fruit equivalents” of damaged fruit. For example, if a plant had 2 damaged fruits, where half of each fruit w...
Datafile (Data File Name: “Datafile_Seed_Number_per_Fruit.csv) contains data on the number of see... more Datafile (Data File Name: “Datafile_Seed_Number_per_Fruit.csv) contains data on the number of seeds per fruit for long-term demographic study of Clarkia xantiana xantiana from 2006 to 2017. At each site, in each year, the number of fruits was counted on up to 150 plants per population. From 2006 to 2012, only undamaged fruit were collected. From 2013 to 2016, up to 30 undamaged and 30 damaged fruits were collected from separate plants.
Datafile (Data File Name: “Datafile_Fruiting_Plant_Density.csv) describes the fruiting plant numb... more Datafile (Data File Name: “Datafile_Fruiting_Plant_Density.csv) describes the fruiting plant number in quadrats followed on permanent transects for long-term demographic study of Clarkia xantiana xantiana from 2006 to 2017. At each site, in each year, fruiting plant number was counted in between 30 and 150 0.5 m2 quadrats distributed haphazardly throughout site. The number of quadrats depends on the areal extent of the population. For the 20 populations included in the detailed demography studies, data from 30 permanent plots are included.
The dataset (Data File Name: “Datafile_Fruit_Number_per_Plant.csv”) describes the fruit productio... more The dataset (Data File Name: “Datafile_Fruit_Number_per_Plant.csv”) describes the fruit production per plant for up to 150 plants for each of the 35 populations followed in a long-term demographic study of Clarkia xantiana xantiana in Ker Co., CA. At each site, in each year, the number of fruits per plant was recorded on up to 150 plants per population. From 2006-2012, fruit number per plant was scored as the sum of undamaged fruits plus the “undamaged fruit equivalents” of damaged fruit. For example, if a plant had 2 damaged fruits, where half of each fruit was missing, the number of undamaged fruit equivalents was scored as 1, and added to the number of undamaged fruits. From 2013-2017, undamaged and damaged fruits were scored separately.
Site locations and environmental variables of 35 populations of Clarkia xantiana ssp. xantiana wh... more Site locations and environmental variables of 35 populations of Clarkia xantiana ssp. xantiana where plant density and fruit production have been measured in a long term demographic study. The datafile (Data File Name: Datafile_Site_Environment.csv) details the full names of the sites, locality information, lat/long locations, slope, elevation, soil parent material, and radiation factors. The README file describes all of the column names in detail.
Darwin’s theory of natural selection successfully explains why organisms are designed to meet env... more Darwin’s theory of natural selection successfully explains why organisms are designed to meet environmental challenges, his simple proposal being that heritable traits that confer survival benefits on individuals will come to predominate in populations (Darwin 1859). Thus, it was a special challenge for him to explain the evolution of secondary sex characters that impair survival in animals. His proposed solution was the theory of sexual selection, according to which features that enhance mating success can evolve despite a possible survival cost (Darwin 1871). This original concept and its recent refinements (see reviews in Andersson 1994; M∅ller 1994; Andersson and Iwasa 1996) were inspired by obvious patterns. For example, it is easy to distinguish female and male peafowl by sight at a great distance, and the males’ exaggerated tails clearly appear to hinder locomotion and camouflage.
The immediate capacity for adaptation under current environmental conditions is directly proporti... more The immediate capacity for adaptation under current environmental conditions is directly proportional to the additive genetic variance for fitness, VA(W). Mean fitness, W, is predicted to change at the rate (VA(W))/W, according to Fishers Fundamental Theorem of Natural Selection. Despite ample research evaluating degree of local adaptation, direct assessment of VA(W) and the capacity for ongoing adaptation is exceedingly rare. We estimated VA(W) and total lifetime fitness in three pedigreed populations of the annual Chamaecrista fasciculata, over three consecutive years in the wild. Contrasting with prevailing expectations of minimal VA(W), we found significant VA(W) in all populations and years, predicting increased mean fitness (0.83 to 6.12 seeds per individual). Further, we identified two instances predicting evolutionary rescue, where selection on standing VA(W) was expected to increase fitness of declining populations (W < 1.0) to levels consistent with population sustainab...
The co-occurrence of several dimensions of resource separation between coexisting consumers stren... more The co-occurrence of several dimensions of resource separation between coexisting consumers strengthens the hypothesis that the separation arose from and/or ameliorates interspecific competition. The two most common pollinators of the California endemic plant Clarkia xantiana ssp. xantiana (Onagraceae), the bees Hesperapis regularis (Mellitidae) and Lasioglossum pullilabre (Halictidae), are known to partition flower resources by flower colour. Here we asked whether H. regularis and L. pullilabre also partition flower resources by diurnal foraging schedule and by food type (pollen versus nectar). We also quantified diurnal patterns of nectar availability, expected to be related to foraging schedules and forager responses to flower colour. The diurnal schedules of the two species differed distinctly and significantly. The majority of L. pullilabre foraging visits occurred before midday, while the majority of H. regularis visits occurred afterwards. The two species foraged for alternat...
ABSTRACT Background/Question/Methods Whether closely related species can coexist is expected to d... more ABSTRACT Background/Question/Methods Whether closely related species can coexist is expected to depend on their evolutionary divergence in niches, relative to their evolutionary divergence in competitive ability. Also critical is the spatial scale at which niche differences appear. Even if close relatives exhibit strongly conserved environmental responses at large geographic scales, they may be able to coexist if their niches differ sufficiently at smaller (i.e., within-community) scales where neighborhood competition and population processes play out. To characterize the spatial scales at which niche differences appear between close relatives, we carried out hierarchical spatial analysis of environmental variation, distribution, and performance in the California-endemic annual plants Clarkia xantiana ssp. xantiana and C. speciosa ssp. polyantha, which have broadly overlapping geographic ranges and sometimes co-occur on smaller scales. Results/Conclusions At the scale of their entire ranges, the distributions of the two species are determined very similarly by variation in climate but differ somewhat in their associations with topography and soils, C. speciosa ssp. polyantha’s presence being associated with shallower slopes, more southerly aspects, and a broader range of substrates. More distinct species-presence associations with topography and substrate appeared at the scale of hundreds of meters, a pattern mirrored by species differences in relationships between abundance, reproductive performance, topography, and soil texture at scales of meters to tens of meters. At the neighborhood scale (centimeters to decimeters), however, individual distribution and performance (water status and biomass) and were spatially structured but not detectably associated with environmental variation. We hypothesize that species differences in plant-soil relations across many scales underlie some degree of spatial separation and allow species coexistence, despite strong similarity in climatic niche, while stochastic processes play a larger role in individual distribution at the smallest scales.
While the idea that water stress contributes to geographic range limits in arid-land plants is we... more While the idea that water stress contributes to geographic range limits in arid-land plants is well founded, it remains to be determined how environmental sources of water stress help determine—along with other environmental, demographic, and evolutionary genetic ...
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