Abstract
Abstract The biotic interactions hypothesis posits that biotic interactions are more important drivers of adaptation closer to the equator, evidenced by “stronger” contemporary interactions (e.g., greater interaction rates) and/or patterns of trait evolution consistent with a history of stronger interactions. Support for the hypothesis is mixed, but few studies span tropical and temperate regions while experimentally controlling for evolutionary history. Here, we integrate field observations and common garden experiments to quantify the relative importance of pollination and herbivory in a pair of tropical‐temperate congeneric perennial herbs. Phytolacca rivinoides and P. americana are pioneer species native to the Neotropics and the eastern United States , respectively. We compared plant–pollinator and plant–herbivore interactions between three tropical populations of P. rivinoides from Costa Rica and three temperate populations of P. americana from its northern range edge in Michigan and Ohio. For some metrics of interaction importance, we also included three subtropical populations of P. americana from its southern range edge in Florida. This approach confounds species and region but allows us, uniquely, to measure complementary proxies of interaction importance across a tropical‐temperate range in one system. To test the prediction that lower‐latitude plants are more reliant on insect pollinators, we quantified floral display and reward, insect visitation rates, and self‐pollination ability (autogamy). To test the prediction that lower‐latitude plants experience more herbivore pressure, we quantified herbivory rates, herbivore abundance, and leaf palatability. We found evidence supporting the biotic interactions hypothesis for most comparisons between P. rivinoides and north‐temperate P. americana (floral display, insect visitation, autogamy, herbivory, herbivore abundance, and young‐leaf palatability). Results for subtropical P. americana populations, however, were typically not intermediate between P. rivinoides and north‐temperate P. americana , as would be predicted by a linear latitudinal gradient in interaction importance. Subtropical young‐leaf palatability was intermediate, but subtropical mature leaves were the least palatable, and pollination‐related traits did not differ between temperate and subtropical regions. These nonlinear patterns of interaction importance suggest future work to link interaction importance to climatic or biotic thresholds. In sum, we found that the biotic interactions hypothesis was more consistently supported at the larger spatial scale of our study.
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Claims 6
Claim · model-written summary
Comparisons of floral display, insect visitation and autogamy between tropical P. rivinoides and northern P. americana supported the biotic interactions hypothesis.
- Taxon
- P. rivinoides
Phytolacca rivinoidese0 - Outcome
- floral display, insect visitation, autogamye0
- Comparator
- north‐temperate P. americanae0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We found evidence supporting the biotic interactions hypothesis for most comparisons between P. rivinoides and north‐temperate P. americana (floral display, insect visitation, autogamy, herbivory, herbivore abundance, and young‐leaf palatability).”
Claim · model-written summary
Comparisons of herbivory, herbivore abundance and young-leaf palatability between tropical P. rivinoides and northern P. americana supported the biotic interactions hypothesis.
- Taxon
- P. rivinoidesPhytolacca rivinoidese0
- Outcome
- herbivory, herbivore abundance, and young‐leaf palatabilitye0
- Comparator
- north‐temperate P. americanae0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“We found evidence supporting the biotic interactions hypothesis for most comparisons between P. rivinoides and north‐temperate P. americana (floral display, insect visitation, autogamy, herbivory, herbivore abundance, and young‐leaf palatability).”
Claim · model-written summary
Subtropical P. americana interaction results were generally not intermediate between tropical and northern populations.
- Taxon
- P. americana
.jpg?width=60)
Phytolacca americanae0 - Outcome
- typically not intermediatee0
- Comparator
- P. rivinoides and north‐temperate P. americanae0
- Setting
- subtropicale0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
e0“Results for subtropical P. americana populations, however, were typically not intermediate between P. rivinoides and north‐temperate P. americana”
Claim · model-written summary
Subtropical young-leaf palatability was intermediate.
- Taxon
- P. americanaPhytolacca americanae1
- Outcome
- young‐leaf palatabilitye0
- Direction
- intermediatee0
- Setting
- Subtropicale0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Subtropical young‐leaf palatability was intermediate”
e1“subtropical populations of P. americana”
Claim · model-written summary
Subtropical mature leaves were the least palatable.
- Taxon
- P. americanaPhytolacca americanae1
- Outcome
- mature leaves were the least palatablee0
- Direction
- leaste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“subtropical mature leaves were the least palatable”
e1“subtropical populations of P. americana”
Claim · model-written summary
Pollination-related traits did not differ between temperate and subtropical P. americana regions.
- Taxon
- P. americanaPhytolacca americanae1
- Outcome
- pollination‐related traitse0
- Direction
- did not differe0
- Comparator
- temperate and subtropical regionse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“pollination‐related traits did not differ between temperate and subtropical regions”
e1“subtropical populations of P. americana”