Biogeography of pollination under climate change: integrating pollinator effectiveness into species distribution models for mango in South Africa

Pollination by wild insects is vital for maintaining ecosystems and food security, but climate change is altering the biogeography of many pollinator species. While progress has been made in assessing climate-driven range shifts using species distribution models (SDMs), most assume all pollinators are functionally equivalent. Here, we introduce a biogeographic approach that integrates Pollen Deposition Effectiveness (PDE), a quantitative metric of species pollination function, with SDMs by summing PDE values of co-occurring pollinators to assess climate-driven changes in both pollinator distributions and their capacity to deliver pollination services. We demonstrate this approach using mango (Mangifera indica) pollinators in South Africa. We identified 61 mango flower visitors, quantified PDE for 38 pollinating species and projected changes in climatically suitable habitat under two climate scenarios (RCP4.5 and RCP8.5) using SDMs. Both species richness and PDE-weighted pollination provision are predicted to decline across core mango-growing regions, alongside substantial species turnover. We find similar spatial patterns of PDE-weighted and unweighted SDMs, indicating high functional redundancy and identify some over-performing pollinators which could be the focus of targeted conservation efforts. We believe this functional approach enhances SDM outputs and provides greater insight for assessing climate change impacts on ecosystem services.

Highlights

We used pollination efficiency calculations and species distribution models (SDMs) to assess potential declines of important mango pollinators in South Africa (Limpopo, Mpumalanga and KwaZulu-Natal provinces).

We identified members of Hymenoptera and Diptera as the most common mango pollinators, while members of Coleoptera, Lepidoptera and Hemiptera do not transfer mango pollen or there are insufficient data to assess them.

We identified smaller species such as those belonging to Calliphoridae and small bees like Liotrigona species were the most efficient mango pollinators.

We identified 38 mango-pollinating insects and found an overall decrease in their future suitable habitat under RCP4.5 and RCP8.5 climate scenarios.

A decrease in mango pollination could decrease mango production, affecting more than 10,000 people working in mango processing and support industries, many smallholder farmers who operate in the informal market and those who grow mango for personal consumption.