1. Introduction
The Earth’s average temperature is projected to increase by 0.3–4.8 ºC by the close of the twenty-first century, as reported by the Intergovernmental Panel on Climate Change (Stocker et al., 2014). Human-induced climate change represents a destructive force that directly and indirectly threatens biodiversity. The rising trend in climate change has wrought irrevocable changes in ecosystems’ structure, composition, services, and stability (Thuiller, 2007; Weiskopf et al., 2020). Various species respond differently to this phenomenon, including adaptation, phenology alterations, and the pursuit of suitable climatic conditions (Robinet & Roques, 2010; Couet et al., 2022). Species failing to adapt to these altered conditions may attempt migration, but if they cannot disperse, they face the grim prospect of local or global extinction (Thuiller et al., 2008; Bellard et al., 2012). Climate change can potentially provoke shifts in species’ distribution ranges at varying scales, affecting individual populations and entire ecosystems (Karl et al., 2009). Numerous studies have documented the occurrence of ”uphill retreats” in various taxa as a response to climate change (Thomas et al., 2006).
Given the pervasive impact of ongoing climate change across the globe, recent research has been intensely focused on predicting its effects on species’ ranges. These efforts aim to develop management strategies to mitigate adverse consequences (Huang et al., 2023; Chowdhury, 2023; Song et al., 2023). Ecologists have underscored the challenge of biodiversity forecasting over the past two decades and have called for adopting predictive ecology (Mouquet et al., 2015). Over nearly four decades, ”species distribution models” (SDMs) were initially conceived as snapshots of species distribution (Stanton et al., 2012). Today, SDMs are recognized as one of the most widely employed tools for evaluating species vulnerability in response to environmental changes (Guisan & Zimmermann, 2000; Zachariah Atwater & Barney, 2021). SDMs find application in diverse areas, including the protection of endangered species, habitat management and restoration, environmental risk assessment, invasive species control, and forecasting species’ range expansion or contraction under the influence of climate change (Franklin, 2010; Zurell et al., 2020). Numerous studies have explored the repercussions of climate change on species’ spatial distribution (e.g., Behroozian et al., 2020; Baumbach et al., 2021; Karami et al., 2022; Naqinezhad et al., 2022; Wani et al., 2022; Shaban et al., 2023). The variability in predictions from different SDMs often presents challenges in result interpretation. To mitigate the uncertainty in SDM forecasts, a practical approach is to employ an ensemble modeling framework, enhancing projections’ precision (Araujo & New, 2007; Marmion et al., 2009; Naimi et al., 2022).
Top of Form
Addressing the impact of global changes on species’ niche dynamics poses a significant challenge for ecologists. This challenge underscores the necessity of employing techniques for analyzing and quantifying distinctions among species’ niches. Ecologists have developed various approaches and metrics for scrutinizing species’ niche dynamics across spatial and temporal scales (Broennimann et al., 2012). A central question in niche theory revolves around whether species maintain or diverge from their ecological niches (Vaissi and Rezaei, 2022). Niche conservatism, a biological concept, characterizes the inclination of species to adhere to their ancestral niches (Wiens & Graham, 2005; Vaissi & Rezaei, 2022; Du et al., 2023; Han et al., 2023). Climate change has brought niche conservatism into focus as a potential concern and threat to organisms (Wiens et al., 2010; Aguirre‐Gutiérrez et al., 2015). Niche divergence occurs when species occupy niches distinct from their ancestral ones (Vaissi and Rezaei, 2022). While niches’ distribution and speciation patterns often remain conserved over time, divergence drives species diversity along ecological gradients (Wiens & Graham, 2005; Vaissi & Rezaei, 2022). Given the rapid pace of global change, understanding whether species alter their niches over time and space has gained paramount importance. Consequently, various tests and criteria have been devised to quantify niche shifts (Guisan et al., 2014). Niche conservatism challenges the transferability of Species Distribution Models (SDMs) predictions (Zachariah Atwater and Barney, 2021). One of the most crucial applications of niche dynamic analysis is the potential to transfer ecological niches, using SDMs, to new geographical and temporal scales, thereby facilitating SDM-based management applications. Such spatial and temporal model transfers find utility in designing conservation areas, introducing new species, and predicting species responses to climate change (Zhu & Peterson, 2017; Yates et al., 2018; Sequeira et al., 2018; Liu et al., 2022).
The genus Ziziphus sp. (Rhamnaceae) encompasses approximately 100-170 species of deciduous and evergreen trees and shrubs, primarily distributed in tropical and subtropical regions (Saied et al., 2008; Baghazadeh-Daryaii et al., 2017). Among these species, Christ’s thorn jujube (Ziziphus spina-christi ) stands out as a native and pivotal species in the Middle East, displaying remarkable resilience to drought and heat stress. Its global distribution spans North Africa, the Arabian Peninsula, India, Lebanon, Iraq, Pakistan, Afghanistan, and Iran (Saied et al., 2008; Rojas-Sandoval, 2022). In Iran, Z. spina-christi is nearly ubiquitous within the Sahara-Sindian (Khalijo-Omanian) region. Another noteworthy species, the Wild jujube (Z. nummularia ), is a deciduous shrub found in India, Pakistan, Iraq, and Iran (Pandey et al., 2010). Its distribution primarily concentrates in the southwest of Iran. Both Z. spina-christi and Z. nummularia play a pivotal role in soil and water conservation, wind and water erosion control, and overall ecosystem sustainability in arid and semi-arid environments (Saied et al., 2008; Pandey et al., 2010; Rojas-Sandoval, 2022).
Data concerning the potential impacts of climate change on these invaluable species remain limited. Predicting changes in species’ ranges under climate shifts is essential to guide conservation efforts effectively. In this study, Species Distribution Models (SDMs) were employed to forecast the potential consequences of climate change on the range expansion or contraction of the two Ziziphus species while considering their climate niche divergence or conservatism.
Top of Form
Our primary objectives were to address the following questions: (1) How will the climatic niches’ dimensions and spatial patterns of the twoZiziphus species change in response to climate warming? (2) Which evolutionary hypotheses govern these two species—conservatism or divergence? (3) Do these two species remain faithful to their established climatic niches, and what implications does this have for their transferability?
Top of Form
Bottom of Form