1. Introduction

Pollination is an ecosystem service and a production practice [1]. At present, an increasing degree of attention is being given to pollination ecosystem service and its economic value due to its linkage to the world food production; on top, it has become a frequently mentioned example of how ecosystems services are economically valuable [2]. Pollination makes a very significant contribution for the production of a broad range of crops, in particular fruits, vegetables, fiber crops, and nuts. Its value is derived from its contribution to the maintenance of ecosystems as well as its impact on agriculture [3]. However, pollinators' decline all over the world has consequences in many agricultural areas and is a major global environmental concern [4]. Thus, it is necessary to assess the potential significant loss of economic value of pollination [5].

It is increasingly recognized that more studies are needed to enhance our understanding of pollination services [3, 6], their contribution to the ecosystem [2, 7, 8], and agriculture productivity [6, 9, 10]. As well, there is a limited scientific evidence to explain the ongoing debate on pollination ecosystem service and valuation [2, 11, 12], the spatial and temporal trends of pollination benefits [1, 13], landscape impacts on the stability of pollination ecosystem services [14], and the suitability of habitats for sustaining valuable pollinators [15]. There is also a wide variation placed in the economic value of pollinators, and the economic value of pollination services is still at its infancy stage [2, 7, 10, 16]. Likewise, valuation of pollination services is useful to justify the allocation of resources toward conservation practices [17].

Economic valuation of pollination services not only provides information on the economic impacts of pollination decline but also contributes to decisionmaking process concerning selection of alternative mitigation strategies [6]. The first global estimate of the economic value of pollination was provided by Costanza et al. [18]. There is an increasing trend in pollination dependency in both the developed and the developing world [19, 20] and crop yields might also be declined due to pollination shortages [5]. The increasing pollination dependency led to a decline in agricultural production, thereby the demand for agricultural land expected to rise due to pollination absence or decline, particularly in developing countries [21]. In most developing countries, managing pollination services is also limited due to limited understanding of its economic value [22]. Accordingly, pollination is far beyond ecological-economical settings, but rather is a service of global importance threatened by land-use change and agricultural intensification [13, 23]. Therefore, we are aiming to fill the research and knowledge gap with respect to spatial and temporal variation of economic valuation of pollination services. Specifically, the major objectives of this study are: the first one is to quantify the economic value of pollination (EVP), the crop vulnerability ratio (CVR) or the potential relative production value loss attributable to lack of or disappearance of pollinators, and the pollination's contribution to total farm gate value (PCV) or the potential relative agricultural sector production value loss attributable to lack of or disappearance of pollinators in Ethiopia. The second objective is to map and assess the temporal and spatial variation of EVP, CVR, and PCV in Ethiopia. Similar to Gallai et al. [5], our study is based on the hypothesis that the economic impact of pollinators on agricultural output is measurable through the use of dependence ratios quantifying the impact of a lack of or disappearance of pollinators on crop production value using a bio-economic approach. Thus, our study focuses on: the analysis of spatial and temporal variation in economic valuation of pollination services and the vulnerability of national economies on pollination benefits; and the use of zonal level data (at local level) to derive mapping of economic valuation pollination, pollination dependency, and vulnerability due to pollination decline.
