Estimating consequences of losing pollination services: an evaluation of the pollinator dependency of plants

Abstract

Exponential population growth and the increased demand of land for food production present the challenge to secure enough food for everyone whilst preserving natural landscapes and biodiversity. The targets of biodiversity conservation and food production have been historically perceived as conflicting, yet the productivity of many crops is maximised by pollinator abundance and diversity. The Ecosystem Service approach addressed this dichotomy by putting emphasis on the benefits that humans obtain from conserving biodiversity. An example is ensuring a diverse food supply by maintaining diverse pollinator communities. Pollinators are intimately connected to our welfare, securing a variety of food and maintaining ecosystem function and health. Consequently, the ongoing global decline of wild pollinators prompted a growing body of research on the extent to which reproductive success of plants is enhanced by flower-visiting animals and how land-use change affects wild pollinators. The overarching aim of this thesis is to understand how losing pollination services can affect human well-being. The objectives of my research are: (1) to elucidate pollinator contribution to wild and crop plants; (2) to develop practical methods for pollination services site-scale assessment; and (3) to pilot the novel tools developed in this thesis in a nature reserve within an agricultural matrix.

Little is known about the potential consequences of losing vertebrate pollinators on plants. I used a systematic review protocol to give an overview of the importance of vertebrate pollinators for the reproductive success of the plants they pollinate. Based on a meta-analysis of 126 experiments on animal-pollinated plants, I found that an exclusion of vertebrates from plants visited by both insects and vertebrate pollinators may reduce fruit and seed production by 63%. Model selection based on Akaike’s Information Criterion (AIC) further revealed that tropical plants are more reliant on vertebrate pollination than their temperate counterparts, and bat-pollinated plants are more dependent on vertebrate pollination than those pollinated by other vertebrates. These findings highlight the potential importance of vertebrate pollinators for the long-term maintenance of both natural and agricultural tropical systems. This study also demonstrated the need for effective conservation action for threatened flower-visiting vertebrate species. More research is needed on the pollination system of plants and their vertebrate pollinators at a community level.

Information on the production dependence of plants on their vertebrate pollinators is scant. Here, I created a dataset of the degrees of production dependence of wild and crop plants on vertebrate pollination based on field exclusion experiments. The database includes information on 126 sites for 29 countries and 90 plants species and information on site details, plants and flower visitors. The production dependence in this dataset can be used for economic valuations of pollination services provided by vertebrates to increase understanding of their importance for food production and the maintenance of natural ecosystems, particularly in the tropics, and to better guide conservation actions.

Currently available tools for pollination service assessment operate at a global or regional scale or rely on high technical expertise. I used expert elicitation techniques to develop a practical tool for the site-scale assessment of pollination services. Three sets of methods were developed to suit different levels of technical expertise and resource availability: desk-based (Red standard method), observational (Amber standard method) and experimental (Green standard method). The novel tool was applied to estimate the value of pollination services provided by a small protected area in Hampshire, UK. The annual net economic value of pollination service in the current state was greater than the alternative state by between £111 and £151 ha-1 year-1.

This thesis adds novel insight into the potential effects of the decline of pollinator taxa in different regions by assessing variations in the reproductive success of wild and crop plants at a global and local scale; thus increasing the much-needed knowledge of the dependence of flowering plants on flower-visiting animals, both invertebrates and vertebrates. The methods developed in this thesis can be useful to a broad range of users including scientists, governments, land managers and conservation practitioners. The accessibility of this tool provides rapid and practical means to generate robust data to inform decision-making in various regions, ecosystems and socio-cultural contexts.

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Identifiers

ORCID for Fabrizia Ratto: orcid.org/0000-0001-8411-4379

ORCID for Kelvin Peh: orcid.org/0000-0002-2921-1341

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