4.2. Climate niche divergence/conservatism
The current investigation, employing niche dynamic analysis, has revealed a noteworthy phenomenon regarding the climatic niche of two species, thereby affirming the concept of niche conservatism (Xian et al., 2023). The niche equivalency test, as applied, demonstrates that the observed overlap in niche characteristics between the two species is more pronounced than expected under random assignment, thus shedding light on the transferability of their climatic niche (Sillero et al., 2022). Notably, the observed overlap in the niche similarity test, while notably more significant than that expected by random assignment or simulation, did not attain statistical significance. Gallego‐Narbón et al. (2023) elucidated that a scenario where the observed overlap is relatively high and the similarity test remains non-significant indicates geographical proximity between the species pairs. This reinforces the outcomes of our study, illustrating that these species are not identical but share similarities within their environmental habitat and are indeed geographically proximate.
The presence of stringent criteria for expansion and high stability criteria point towards these species displaying non-aggressive behavior, with their native niche exhibiting stability and a limited ability to adapt to novel environmental conditions. In simpler terms, these species exhibit fidelity to their existing climatic conditions, actively seeking niches that mirror historical climates (Wang et al., 2023). Our findings align with those of Lustenhouwer & Parker (2022), where the niche conservatism hypothesis remains unchallenged, marked by low expansion criteria and a predominance of niche stability. Furthermore, niche unfilling is evident, with the species utilizing less than half of the available environmental space, contingent on their dispersal capabilities (Keppel et al., 2012). It is imperative to identify areas less susceptible to climate change, called climate macro-refugia, due to the escalating pace of climate change. Given the conserved nature of these species’ climatic niche and their limited adaptability to new climatic conditions, their occurrence is confined to habitats resembling their ancestral or native ranges. Considering the regional topography, physiological and phenological traits, and the constrained seed dispersal resulting from the seeds’ substantial weight, it can be reasonably concluded that these species exhibit limited spatial and temporal transfer capabilities. Consequently, they are highly vulnerable to the impacts of climate change, lacking the natural ability to migrate to habitats projected by species distribution models.