Scaling-up targets for a threatened butterfly: A method to define Favourable Reference Values

Simona Bonelli,Francesca Barbero,Arianna Zampollo,Cristiana Cerrato,Piero Genovesi,Valentina La Morgia

doi:10.1016/j.ecolind.2021.108356

Abstract

The accomplishment of a Favourable Conservation Status (FCS) for habitats and species is the Habitats Directive's primary goal (HD, 92/43/EEC). As tools for assessing the measurable parameters of conservation status, the European Commission identified Favourable Reference Values (FRVs), and it described the methodology to set them. However, examples of its application are rare.We propose a mixed reference-/model-based approach to set the Favourable Reference Population (FRP) and Range (FRR) for a threatened butterfly, Parnassius apollo, in the Italian Alps. The approach involves the use of a habitat suitability map obtained via Maxent as a basis for a clumping procedure to identify discrete patches of suitable habitat (clumps), corresponding to potentially viable local (meta)populations. The number and distribution of clumps occupied by the species along geographical gradients are compared to the distribution of all available clumps to define the FRVs.According to our analyses, 41 clumps are occupied by P. apollo in the Italian Alps. Since their distribution reflects clump availability along all geographical gradients, this value can be used to express the FRP, and to subsequently define the FRR as the envelope including the 41 clumps.Our approach considers several conditions reflecting the species persistence and provides insights for conservation and monitoring. Our objective, transparent method of setting FRVs can be applied to assess FCSs for other threatened species occurring in discrete units, with disjunct populations or local metapopulations.

Highlights

The accomplishment of a Favourable Conservation Status (FCS) for habitats and species is one of the main biodiversity goals of the Habitats Directive (HD, EU 4392/EEC), probably the most important tool for biodiversity conservation in Europe (EU - Epstein, 2013)
The steps of our approach can be summarized as follows: (i) we model habitat suitability for the species in the Italian Alps using Maxent (Philips et al, 2006–2.2.1); (ii) on the map (Fig. S1) resulting from the Species Distribution Modeling (SDM), we apply a clumping procedure which enables to identify discrete patches of suit able habitat, each corresponding to a potentially viable localpopulation (2.2.2); (iii) to scale up the population targets to the level of the Italian Alps, we consider the available knowledge on the past distribution of the species with respect to geographical and ecological conditions (Verity, 1947; Bonelli et al, 2018) and compare the number of available clumps to the number of occupied clumps (2.2.3)
While we can identify the whole Alpine arc as the species’ natural range in the Alpine biogeographical region, several P. apollo populations are strongly declining or have disappeared across the Apennines (Bonelli et al, 2018), which are mostly included in the Mediterranean biogeo graphical region

Summary

Introduction

The accomplishment of a Favourable Conservation Status (FCS) for habitats and species is one of the main biodiversity goals of the Habitats Directive (HD, EU 4392/EEC), probably the most important tool for biodiversity conservation in Europe (EU - Epstein, 2013). As generally defined in Art. 1 of the HD, to achieve an FCS, the species listed in the HD Annexes (II, IV and V) must maintain themselves on a long-term basis as a viable component of their natural habitats. This implies evaluating different parameters (range, population, habitat for the species, future prospects), all of which are indicators of species status and they must reach favourable values for the FCS objective to be met. The appropriate application of the FCS concept requires discus sion and clarification on several, controversial aspects related to the concept itself (Epstein et al, 2015) and to the above-mentioned pa rameters, e.g., whether the FCS should be assessed at the species, pop ulation or national level, and how to strictly interpret the long-term viability requirement

Objectives

Methods

Results

Discussion

Conclusion