International Journal of Molecular Ecology and Conservation 2024, Vol.14, No.5, 218-224 http://ecoevopublisher.com/index.php/ijmec 219 address multiple threats. It is expected to provide reference for future research directions and policy decisions, promote more effective conservation actions, and maintain global biodiversity. 2 Proximate Causes of Species Endangerment 2.1 Habitat loss and fragmentation Habitat loss and fragmentation are widely recognized as the most significant proximate causes of species endangerment. The destruction and division of natural habitats due to human activities such as agriculture, urban development, and deforestation lead to reduced living spaces for species, disrupting their ecological niches and leading to population declines. This fragmentation not only reduces the available habitat but also isolates populations, making it difficult for species to maintain genetic diversity and increasing their vulnerability to extinction (Hernández et al., 2013). 2.2 Overexploitation: hunting, fishing, and wildlife trade Overexploitation through hunting, fishing, and wildlife trade is another critical proximate cause of species endangerment. These activities directly reduce population sizes and can lead to the depletion of species faster than they can reproduce. The unsustainable harvesting of wildlife for food, medicine, and other purposes has been a significant driver of declines in many species, particularly those with high economic value or those that are easily accessible (Kotiaho et al., 2005). 2.3 Pollution and environmental contaminants Pollution and environmental contaminants pose significant threats to species by altering their habitats and directly affecting their health. Contaminants such as pesticides, heavy metals, and industrial chemicals can lead to physiological stress, reproductive failures, and increased mortality rates in wildlife. For instance, amphibians are particularly vulnerable to pollutants, which can disrupt their endocrine systems and increase susceptibility to diseases (Hayes et al., 2010). 2.4 Invasive species and competition with native fauna Invasive species can outcompete native fauna for resources, leading to declines in native populations. These non-native species often have no natural predators in their new environments, allowing them to proliferate unchecked and disrupt local ecosystems. The introduction of invasive species can lead to competition for food, habitat, and other resources, often resulting in the decline or extinction of native species (Hayes et al., 2010). 2.5 Climate change-induced physiological and behavioral disruptions Climate change is increasingly recognized as a proximate cause of species endangerment, affecting species through physiological and behavioral disruptions. Changes in temperature, precipitation patterns, and extreme weather events can alter habitats and food availability, leading to stress and reduced survival rates. Species with limited physiological tolerance to changing climates or those unable to migrate to more suitable habitats are particularly at risk (Selwood et al., 2015; Cahill et al., 2013). 3 Ultimate Causes of Population Decline 3.1 Anthropogenic pressures and habitat modification Anthropogenic pressures, including habitat loss and fragmentation, are significant ultimate causes of population decline. Habitat destruction due to land development, agriculture, and urbanization leads to the loss of critical living spaces for many species, thereby reducing their populations and increasing extinction risk (Hernández et al., 2013). Additionally, climate change, driven by human activities, exacerbates these pressures by altering habitats and affecting species' survival and reproduction (Cahill et al., 2013; Selwood et al., 2015). 3.2 Loss of genetic diversity and reduced adaptive potential The loss of genetic diversity is another ultimate cause of population decline, as it reduces a species' ability to adapt to changing environmental conditions. Small populations are particularly vulnerable to genetic drift, inbreeding depression, and the fixation of deleterious mutations, which can lead to reduced fitness and increased
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