Intraspecific variation in pollination ecology due to altitudinal environmental heterogeneity

TL;DR

This study shows how environmental differences at different altitudes affect the pollination strategies of a plant species in the Venezuelan Andes.

Contribution

The study reveals that environmental heterogeneity, not pollinator differences, drives variation in pollination ecology between plant populations.

Findings

Seed production by natural pollinators was higher at the lower altitude site.

Nectar quality and pollinator visitation rates were greater at the lower altitude.

Higher altitude plants compensated with higher floral density and aggregation to maintain nectar energy.

Abstract

Plant‐pollinator interactions are constrained by floral traits and available pollinators, both of which can vary across environmental gradients, with consequences for the stability of the interaction. Here, we quantified how the pollination ecology of a high‐mountain hummingbird‐pollinated plant changes across a progressively more stressful environmental gradient of the Venezuelan Andes. We compared pollination ecology between two populations of this plant: Piedras Blancas (PB) and Gavidia (GV), 4450 and 3600 m asl, respectively. We hypothesised that self‐compatibility might be higher at the higher altitude site, however we found that flowers showed similar capacities for self‐compatibility in both localities. Seed production by flowers exposed to natural pollinators was significantly higher in the lower locality, where we also found higher nectar quality, larger flowers and increased frequencies of pollinator visitations. Interestingly, the population energy offered in the nectar was the same for both localities due to the higher density and floral aggregation found in the higher altitude population. Our study demonstrates how two plant populations in different environmental conditions have different pollination ecology strategies. Pollinator visitations or their absence result in trait associations in one population that are independent in the other. These population differences are not explained by differences in pollinator assembly, but by environmental heterogeneity.

Plant populations in different eco‐regions differed in pollination ecology strategies. These population differences are not explained by differences in pollinator assembly, but by environmental heterogeneity.

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