Biotic and Anthropogenic Forces Rival Climatic/Abiotic Factors in Determining Global Plant Population Growth and Fitness. Morris, W. F.; Ehrlén, J.; Dahlgren, J. P.; Loomis, A. K.; and Louthan, A. M. Proceedings of the National Academy of Sciences, 117(2):1107–1112, January, 2020.
doi  abstract   bibtex   
[Significance] Knowing which of multiple environmental factors (climate, other species, humans, etc.) most strongly affect wild plants and animals could focus our attention on the future environmental changes most likely to influence biodiversity. However, we find that abiotic, biotic, and human influences on plant populations are of similar strengths, for different kinds of plants and in multiple locations and environments. The effects of these factors on plant evolution are also likely to be similar. Thus, there is unlikely to be a shortcut to considering all of these factors when predicting the future ecological and evolutionary responses of species and of biodiversity to environmental changes. [Abstract] Multiple, simultaneous environmental changes, in climatic/abiotic factors, interacting species, and direct human influences, are impacting natural populations and thus biodiversity, ecosystem services, and evolutionary trajectories. Determining whether the magnitudes of the population impacts of abiotic, biotic, and anthropogenic drivers differ, accounting for their direct effects and effects mediated through other drivers, would allow us to better predict population fates and design mitigation strategies. We compiled 644 paired values of the population growth rate ($\lambda$) from high and low levels of an identified driver from demographic studies of terrestrial plants. Among abiotic drivers, natural disturbance (not climate), and among biotic drivers, interactions with neighboring plants had the strongest effects on $\lambda$. However, when drivers were combined into the 3 main types, their average effects on $\lambda$ did not differ. For the subset of studies that measured both the average and variability of the driver, $\lambda$ was marginally more sensitive to 1 SD of change in abiotic drivers relative to biotic drivers, but sensitivity to biotic drivers was still substantial. Similar impact magnitudes for abiotic/biotic/anthropogenic drivers hold for plants of different growth forms, for different latitudinal zones, and for biomes characterized by harsher or milder abiotic conditions, suggesting that all 3 drivers have equivalent impacts across a variety of contexts. Thus, the best available information about the integrated effects of drivers on all demographic rates provides no justification for ignoring drivers of any of these 3 types when projecting ecological and evolutionary responses of populations and of biodiversity to environmental changes. [Excerpt: Discussion] Our analysis of the best available data shows that there is no one main type of driver (abiotic, biotic, or anthropogenic) that has overwhelmingly stronger effects on plant population growth and fitness relative to the others. [...] Our conclusion based on analysis of the full dataset that changes in abiotic, biotic, and anthropogenic drivers all need to be considered largely holds for plants with different growth forms, for different latitudinal zones, and for both harsher and more benign abiotic environments (as indicated by biome-level NPP). The generality of this result has 4 important ecological and evolutionary implications. [::] First, when predicting how the distributions and abundances of plant species will respond to climate change, considering only the effects of changes in climatic drivers is not likely to yield accurate predictions. Despite widespread recognition that interspecific interactions may influence distributions, the lion's share of work to predict how climate change will shift distributions has used species distribution models (SDMs), which typically use only climate variables (less often nonclimate abiotic variables, and only very rarely biotic variables) as predictors of species' occurrences [...]. However, if the influence of biotic interactions is substantial, even if lower on average than the influence of climate and other abiotic drivers, then changes in the distributions and abundances of interacting species, which may reflect indirect effects of climate change, species introductions, or other environmental changes, may be just as important to weigh as the direct effects of climate change per se. While this warning has often been made in the ecological literature, our finding that the average effect magnitude of biotic drivers is substantial relative to abiotic drivers makes this warning more poignant, and suggests that changes in biotic drivers cannot be safely ignored, unless we know that biotic and abiotic drivers are tightly correlated and will continue to be so as the environment changes. [::] A second important implication of our results is that the effect magnitudes of abiotic, biotic, and anthropogenic drivers defy simple hypotheses about when and where one should be stronger than the others. [...] Our results indicate that both abiotic and biotic forces are influential, both in abiotically benign (e.g., at low latitudes and in high NPP biomes) and in seemingly more challenging environments. [...] Similarly, abiotic stress in harsh environments may have preadapted plants to anthropogenic stress, leading to similar effects of all 3 main driver types in such environments. However, interestingly, we did find that plants at middle and high latitudes and in less productive biomes were more sensitive to drivers of all 3 main types, suggesting that more marginal habitats may increase the influence of all drivers. In contrast, a woody growth form may make plants more resilient on average to changes in all types of drivers. [::] A third important implication of our findings is that, because the strength of the impacts of anthropogenic drivers rivals those of abiotic and biotic drivers, we must always consider the possibility that changes in the ways that humans use or manage landscapes will modify or even overwhelm the effects of changes in climate. [::] Fourth, that no one driver type (abiotic, biotic, or anthropogenic) is overwhelmingly more influential has 3 important evolutionary implications. [...] Because the magnitudes of the effects of abiotic, biotic, and anthropogenic drivers on mean absolute fitness (and thus on the opportunity for selection) are similar, their indirect effects on the strength of selection on traits that do not directly modulate the impacts of those drivers are also likely to be of a similar order of magnitude. [...] [\n] In conclusion, our intention in using the best available information to evaluate effects of drivers on plant population growth and fitness was to look both backward and forward in time. Looking backward, we find no evidence to conclude that abiotic forces have been dramatically more or less influential than biotic forces in shaping the plant traits, abundances, and geographical distributions that we see today. Looking forward, our findings make it clear that we must simultaneously account for abiotic, biotic, and (increasingly, given growth in human population size and per-capita resource consumption) anthropogenic forces if we are to accurately forecast the ecological and evolutionary futures of terrestrial plants (and thus ecosystem services such as carbon sequestration in which they play a disproportionate global role). [...]
@article{morrisBioticAnthropogenicForces2020,
  title = {Biotic and Anthropogenic Forces Rival Climatic/Abiotic Factors in Determining Global Plant Population Growth and Fitness},
  author = {Morris, William F. and Ehrl{\'e}n, Johan and Dahlgren, Johan P. and Loomis, Alexander K. and Louthan, Allison M.},
  year = {2020},
  month = jan,
  volume = {117},
  pages = {1107--1112},
  issn = {0027-8424, 1091-6490},
  doi = {10.1073/pnas.1918363117},
  abstract = {[Significance]
Knowing which of multiple environmental factors (climate, other species, humans, etc.) most strongly affect wild plants and animals could focus our attention on the future environmental changes most likely to influence biodiversity. However, we find that abiotic, biotic, and human influences on plant populations are of similar strengths, for different kinds of plants and in multiple locations and environments. The effects of these factors on plant evolution are also likely to be similar. Thus, there is unlikely to be a shortcut to considering all of these factors when predicting the future ecological and evolutionary responses of species and of biodiversity to environmental changes.

[Abstract]
Multiple, simultaneous environmental changes, in climatic/abiotic factors, interacting species, and direct human influences, are impacting natural populations and thus biodiversity, ecosystem services, and evolutionary trajectories. Determining whether the magnitudes of the population impacts of abiotic, biotic, and anthropogenic drivers differ, accounting for their direct effects and effects mediated through other drivers, would allow us to better predict population fates and design mitigation strategies. We compiled 644 paired values of the population growth rate ({$\lambda$}) from high and low levels of an identified driver from demographic studies of terrestrial plants. Among abiotic drivers, natural disturbance (not climate), and among biotic drivers, interactions with neighboring plants had the strongest effects on {$\lambda$}. However, when drivers were combined into the 3 main types, their average effects on {$\lambda$} did not differ. For the subset of studies that measured both the average and variability of the driver, {$\lambda$} was marginally more sensitive to 1 SD of change in abiotic drivers relative to biotic drivers, but sensitivity to biotic drivers was still substantial. Similar impact magnitudes for abiotic/biotic/anthropogenic drivers hold for plants of different growth forms, for different latitudinal zones, and for biomes characterized by harsher or milder abiotic conditions, suggesting that all 3 drivers have equivalent impacts across a variety of contexts. Thus, the best available information about the integrated effects of drivers on all demographic rates provides no justification for ignoring drivers of any of these 3 types when projecting ecological and evolutionary responses of populations and of biodiversity to environmental changes.

[Excerpt: Discussion]
Our analysis of the best available data shows that there is no one main type of driver (abiotic, biotic, or anthropogenic) that has overwhelmingly stronger effects on plant population growth and fitness relative to the others. [...] Our conclusion based on analysis of the full dataset that changes in abiotic, biotic, and anthropogenic drivers all need to be considered largely holds for plants with different growth forms, for different latitudinal zones, and for both harsher and more benign abiotic environments (as indicated by biome-level NPP). The generality of this result has 4 important ecological and evolutionary implications.

[::] First, when predicting how the distributions and abundances of plant species will respond to climate change, considering only the effects of changes in climatic drivers is not likely to yield accurate predictions. Despite widespread recognition that interspecific interactions may influence distributions, the lion's share of work to predict how climate change will shift distributions has used species distribution models (SDMs), which typically use only climate variables (less often nonclimate abiotic variables, and only very rarely biotic variables) as predictors of species' occurrences [...]. However, if the influence of biotic interactions is substantial, even if lower on average than the influence of climate and other abiotic drivers, then changes in the distributions and abundances of interacting species, which may reflect indirect effects of climate change, species introductions, or other environmental changes, may be just as important to weigh as the direct effects of climate change per se. While this warning has often been made in the ecological literature, our finding that the average effect magnitude of biotic drivers is substantial relative to abiotic drivers makes this warning more poignant, and suggests that changes in biotic drivers cannot be safely ignored, unless we know that biotic and abiotic drivers are tightly correlated and will continue to be so as the environment changes.

[::] A second important implication of our results is that the effect magnitudes of abiotic, biotic, and anthropogenic drivers defy simple hypotheses about when and where one should be stronger than the others.  [...] Our results indicate that both abiotic and biotic forces are influential, both in abiotically benign (e.g., at low latitudes and in high NPP biomes) and in seemingly more challenging environments.  [...] Similarly, abiotic stress in harsh environments may have preadapted plants to anthropogenic stress, leading to similar effects of all 3 main driver types in such environments. However, interestingly, we did find that plants at middle and high latitudes and in less productive biomes were more sensitive to drivers of all 3 main types, suggesting that more marginal habitats may increase the influence of all drivers. In contrast, a woody growth form may make plants more resilient on average to changes in all types of drivers.

[::] A third important implication of our findings is that, because the strength of the impacts of anthropogenic drivers rivals those of abiotic and biotic drivers, we must always consider the possibility that changes in the ways that humans use or manage landscapes will modify or even overwhelm the effects of changes in climate.

[::] Fourth, that no one driver type (abiotic, biotic, or anthropogenic) is overwhelmingly more influential has 3 important evolutionary implications. [...] Because the magnitudes of the effects of abiotic, biotic, and anthropogenic drivers on mean absolute fitness (and thus on the opportunity for selection) are similar, their indirect effects on the strength of selection on traits that do not directly modulate the impacts of those drivers are also likely to be of a similar order of magnitude. [...]

[\textbackslash n] In conclusion, our intention in using the best available information to evaluate effects of drivers on plant population growth and fitness was to look both backward and forward in time. Looking backward, we find no evidence to conclude that abiotic forces have been dramatically more or less influential than biotic forces in shaping the plant traits, abundances, and geographical distributions that we see today. Looking forward, our findings make it clear that we must simultaneously account for abiotic, biotic, and (increasingly, given growth in human population size and per-capita resource consumption) anthropogenic forces if we are to accurately forecast the ecological and evolutionary futures of terrestrial plants (and thus ecosystem services such as carbon sequestration in which they play a disproportionate global role). [...]},
  copyright = {Copyright \textcopyright{} 2020 the Author(s). Published by PNAS.. https://creativecommons.org/licenses/by-nc-nd/4.0/This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).},
  journal = {Proceedings of the National Academy of Sciences},
  keywords = {~INRMM-MiD:z-UW7WZH76,abiotic-factors,anthropogenic-impacts,biotic-factors,climate-change,comparison,complexity,feedback,forest-resources,human-impact,seminal,vegetation},
  language = {en},
  lccn = {INRMM-MiD:z-UW7WZH76},
  number = {2},
  pmid = {31888999}
}
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