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).
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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.
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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?
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