Climate Change and Biodiversity Shifts: Predicting Species Losses and Gains – Methodology

Climate Change and Biodiversity Shifts: Predicting Species Losses and Gains – Methodology Isabel M. Vique1, Catherine Numa2, Faye Weaver2 1 IUCN World Commission on Protected Areas and Species Survival Commission, Iguana Specialist Group 2 IUCN Centre for Mediterranean Cooperation, Málaga, Spain December 2025 This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 101037084. This publication reflects only the author's views and the European Community is not liable for any use that may be made of the information contained herein. Contents 1. Introduction ....................................................................................................................... 3 2. Methodology ..................................................................................................................... 4 2.1 Data collection ............................................................................................................. 4 2.1.1 Species occurrences ............................................................................................. 5 2.2 Data processing ........................................................................................................... 6 2.2.1 IUCN Red List data ............................................................................................... 6 2.2.2 Regional dataset of species presence ................................................................... 6 2.2.3 Restricted Range species ..................................................................................... 7 2.3 Species losses and gains prediction analysis .............................................................. 7 2.3.1 Scores assigned to each criterion ......................................................................... 9 3. Results ............................................................................................................................ 10 3.1 Proportion of Ebro Delta species assessed on the IUCN Red List ............................. 10 3.2 Restricted range species in Ebro Delta ...................................................................... 11 3.3 Potential losses and gains of species in Ebro Delta ................................................... 11 4. Conclusions and caveats ................................................................................................ 12 References ......................................................................................................................... 13 1. Introduction In a rapidly changing world where climate change is increasingly impacting both human and wildlife populations, conservationists require effective methods to anticipate, mitigate and adapt to its effects on species distributions. Here, we present a methodology to standardise the process of identifying potential species gains and losses at specific sites due to the effects of climate change, using data from the IUCN Red List of Threatened Species™ and other available biodiversity databases. The IUCN Red List is a critical indicator of the health of the world’s biodiversity. Far more than a list of species and their status, it provides information about range, population size, habitat and ecology, use and/or trade, threats, and conservation actions that will help inform necessary conservation decisions. This analysis was piloted in the Ebro Delta on the coast of Catalonia, Spain, a unique ecosystem which is particularly vulnerable to the impacts of climate change (Figure 1). The Ebro Delta is home to over to more than 500 species, one in five of which are threatened with extinction (classified as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU)) on the IUCN Red List, including several endemic species, making it a critical site for biodiversity as well as supporting livelihoods in the region, being an important area for agricultural production. Using the methodology presented here, we reviewed a wide range of taxa present in the Ebro Delta to assess their potential losses and gains under the impacts of climate change. Figure 1. The Ebro Delta study area (De la Cruz & Numa, 2024). 2. Methodology A systematic framework was developed to evaluate potential losses and gains in species distributions under the impacts of climate change (Figure 2). The analysis consists of four main steps: 1. Data collection 2. Data processing and species selection 3. Application of the loss and gains framework criteria 4. Analysis and discussion of results Figure 2. The protocol for assessing potential losses and gains in species distributions under the impacts of climate change presented in the current methodology 2.1 Data collection In order to create a Master List of species present in the study site, we collated information from the IUCN Red List of Threatened Species™ (IUCN, 2025), as well as a regional database of species occurrences in the study area (Global Biodiversity Information Facility (GBIF)) and the Restricted Range of the IUCN Key Biodiversity Areas (KBA) Standard (IUCN, 2016). While acknowledging the limitations of relying solely on Red List assessments to forecast future biodiversity changes, and recognising the strengths of more sophisticated modelling approaches, this method provides a practical and accessible first step for obtaining a broad picture of likely species distribution dynamics in a given site or region under climate change. Information on species occurrences from the Red List was confirmed using local biodiversity data; for the Ebro Data we sourced this data from the GBIF Catalan Biodiversity Database (Banc de dades de biodiversitat de Catalunya) (Font et al., 2025). We then cross-referenced the species occurrence data with the Restricted Range criterion of the IUCN KBA Standard, ensuring to give particular attention to species with limited distributions. 2.1.1 Species occurrences IUCN Red List data: First, to develop a dataset of species likely to be present in the Ebro Delta (hereafter Master List) and compile their corresponding distribution shapefiles, data for species with range maps overlapping the study site was downloaded from the IUCN Red List database 1 . Regional database of species occurrences: If available, regional or local databases of species occurrences within the study site or region should be used as the basis for the Master List of species presence. The most accurate, up-to-date and high-spatial resolution available species data for the study site should be used. For the Ebro Delta, the best available local species data was the Catalan Biodiversity Database, compiled by the Generalitat de Catalunya and the Universitat de Barcelona. All the available datasets for this study site were downloaded from the Catalan Biodiversity Database on GBIF: 1. FloraCAT (Font, 2025): Data bank for Cormophytes in Catalonia. 2. VerteCAT (Ferrer, 2025): Data bank for vertebrates in Catalonia. 3. AlgaCAT (Gómez Garreta et al., 2025): Data bank for algae in Catalonia. 4. FungaCAT (Llistosella, 2025): Data bank for Fungi in Catalonia. 5. ArtroCat (Serra, 2025): Data bank for Arthropods in Catalonia. 6. LiquenCAT (Hladun, 2025): Data bank for Lichen in Catalonia. 7. BrioCAT (Brugués & Cros, 2025): Data bank for Bryophytes in Catalonia. Restricted range species: Following the definition of restricted range from the IUCN KBA Standard (KBA Standards and Appeals Committee of IUCN SSC/WCPA, 2022), which defines range-restricted species as those whose range is in the lower quartile of a given taxonomic group, to a maximum of 50,000 km², we obtained information about species present in the site that are considered of restricted range. This information is available on the KBA tools webpage, but it should be noted that this is non-exhaustive, because it relies on maps that have been submitted along with species Red List assessments. 1 Note: The IUCN Red List species range information comprises broad-scale representations of species distributions and does not confirm species presence within a particular site. 2.2 Data processing 2.2.1 IUCN Red List data A series of steps were followed to refine the Master List, narrowing it down to species that are most likely to be present in the study site (Ebro Delta): 1. We filtered all the species with a map distribution within 50 km of the Ebro Delta on the Red List database. GIS tools were used to examine the species distribution polygons and exclude all species whose distributions did not overlap with the study site. 2. IUCN Red List data was filtered by Presence, Origin and Seasonality fields (Table 1). Table 1. Values for presence, origin and seasonality fields in IUCN Red List spatial data. Ranges associated with the values shown in grey were excluded from the final Master List of species. Presence Origin Seasonality 1 (Extant) 1 (Native) 1 (Resident) 2 (Probably Extant) 2 (Reintroduced) 2 (Breeding Season) 3 (Possibly Extant) 3 (Introduced) 3 (Non-breeding Season) 4 (Possibly Extinct) 4 (Vagrant) 4 (Passage) 5 (Extinct) 5 (Origin Uncertain) 5 (Seasonal occurrence uncertain) 6 (Presence Uncertain) 6 (Assisted Colonisation) 3. Following the previous steps, the species determined to be present within the site were retained in the Master List, along with their corresponding information relevant to the analysis, including Red List Category, Red List Criteria, Threats, Population trend and System where the species lives (Figure 1). 2.2.2 Regional dataset of species presence We collected data from the seven GBIF datasets in one Excel sheet and filtered by location, selecting only the species reported to be located in the Ebro Delta. This list was then cross-referenced with the IUCN Red List data using the formula COUNTIF to determine how many of the species recorded in the Ebro Delta had been assessed on the Red List, and how many species assessed on the Red List had been confirmed by local research (i.e., included in the regional GBIF database). The species that have been assessed on the Red List were retained in the Master List. We applied the losses and gains framework to all the species on the final Master List, which comprised all species that are present in the Ebro Delta according to the Catalan Biodiversity Database that are also assessed on the IUCN Red List (Figure 3). A total of 218 species were found identified from both sources and included in the Master List. Figure 3. Preview of the Master List of species present in the Ebro Delta collated in this analysis 2.2.3 Restricted Range species The KBA data on restricted range species was cross-referenced with the species Master List to investigate whether any of the species in the study site were considered to have restricted range, using the formula COUNTIF. All non-threatened (Near Threatened (NT), Least Concern (LC) and Data Deficient (DD)) species were subsequently cross-referenced with the Restricted Range data to identify species which are not currently considered threatened but could be particularly sensitive to changes in habitat conditions. 2.3 Species losses and gains prediction analysis Following the approach developed by Thomas et al. (2010), we developed a series of criteria as a framework for the quantitative analysis of potential losses and gains in species distributions under the impacts of climate change (Table 2). We designed this framework based on information available on the Red List, such as Red List Category, habitat conditions, niche specialisation and restricted range, which are available for species globally and can be used to infer information about their potential responses to environmental change, including the impacts of climate change. Where available, regional scale Red List assessments relevant to the study site should be used for this analysis, as the information and spatial data will likely be higher resolution and more specific to the study area than global scale Red List assessments. We conducted a literature review to identify criteria which can help predict whether species in a given site will experience losses or gains in their distributions under climate change. The following criteria were identified as relevant for the analysis and included in the framework: a. Red List Category: Species threatened with extinction are expected to be more sensitive to new threats and changes in habitat than Data Deficient (DD), Near Threated (NT) and Least Concern (LC) species. Any non-threatened species (NT, LC or DD) which are considered to have a restricted range are likely to be less adaptable to losses or shifts in habitat, despite not currently facing severe threats. b. IUCN Red List Criteria: Based on available literature (Akçakaya et al., 2006; Foden & Young, 2016; IUCN Standards and Petitions Committee, 2024), Red List Criteria A3, A4, B1, B2, C1, C2, D2 and E can indicate a higher sensitivity to new threats and changes in habitat associated with climate change. However, not being associated with these specific criteria doesn’t necessarily provide an advantage against climate change, so those species are assigned a neutral score. c. Threats: Threats directly related to climate change, from the IUCN Species Information Service (SiS) subdirections, indicate if a species is already affected or expected to be affected by the effects of climate change. d. Population trend: Species with decreasing populations are expected to be particularly sensitive to new threats and changes in habitats brought about by climate change than species with populations that are stable or increasing despite the effects of climate change. e. Habitat: Species described as habitat generalists or tolerant of anthropogenic environments (e.g., farmland, urban areas) are likely to be more resilient to changes in their environment, including the effects of climate change. These species are expected to be more capable of adapting to environmental changes by expanding their range and potentially even growing their populations, whereas other, more sensitive species will likely recede or experience population reductions. This analysis included a search of terms such as “generalist” and “tolerant” within the Habitat section of the Red List assessments to identify the species which are expected to be more resilient and perhaps even take advantage of the impacts of climate change. Table 2. Criteria applied to assess potential losses and gains for each species, and their associated scores 2.3.1 Scores assigned to each criterion As shown in Table 2, a negative (-1), neutral (0) or positive (+1) score is assigned to each species under each criterion, based on the following considerations: a. Red List Category: Species classified as threatened on the IUCN Red List (i.e., Critically Endangered (CR), Endangered (EN), and Vulnerable (VU)) are assigned a score of -1, reflecting their heightened sensitivity to additional pressures, including those arising from climate change. Species listed as Least Concern (LC) receive a score of +1, indicating a greater potential resilience to climate change impacts. Species categorised as Near Threatened (NT) or Data Deficient (DD) are assigned a score of 0, as these categories neither clearly demonstrate vulnerability nor resilience to additional threats. However, species that are non-threatened (NT, LC or DD) but are of restricted range should be assigned a score of -1. b. Red List Criteria: A score of -1 is given to species assessed under Red List Criteria that suggest high sensitivity to climate change threats, following the frameworks proposed by Akçakaya et al. (2006) and Foden & Young (2016). A score of 0 is assigned to species assessed under other criteria, as the absence of these criteria in their Red List assessment does not directly indicate either increased vulnerability or resilience to climate change. c. Threats: Species for which climate change and severe weather are explicitly identified as primary threats are assigned a score of -1. A score of +1 is given to