In-Depth Notes on Alien Vertebrate Richness in Mountains

Alien vertebrates face significant challenges due to climate change, land-use change, and biological invasions, particularly in mountainous regions where ecosystems are sensitive to such alterations. This study compiled comprehensive occurrence records for 717 alien vertebrate species across 2984 mountains worldwide, providing a robust data set for analysis.

The research analyzed various aspects of alien vertebrate distribution, including biogeographic origin, occurrences in protected areas, and multiple factors influencing alien vertebrate richness. It found that the most frequently recorded alien vertebrates include 318 distinct bird species and 161 mammal species, highlighting the prominence of these taxa in the data set as compared to others like reptiles and amphibians.

Common recipient realms for these species include the Palearctic, Nearctic, and Australasian regions, while the dominant donor realms consist of the Nearctic, Indo-Malay, and Afrotropic biogeographical regions. A noteworthy finding from the study is that nearly 50% of alien species recorded are also found in protected areas, indicating that these spaces play a critical role in the conservation of biodiversity.

The distribution of alien vertebrates is explained through a combination of anthropogenic impacts, such as road density and biodiversity loss, alongside physical mountain characteristics, including elevation range and terrain roughness. This highlights how human activity overlaps significantly with natural processes in shaping species distributions.

Importance of Mountains
Mountains are recognized as biodiversity hotspots, hosting a high level of endemic species, making them vital for ecological retention. They provide crucial ecosystem services such as recreation opportunities, natural hazard protection, and climate regulation, which are increasingly threatened by global change pressures. The escalation of climate change impacts necessitates diligent research on biodiversity and the specifically related impacts of biological invasions in these delicate ecosystems.

Research Questions Addressed
The study aimed to address several key research questions:

  1. Spatial patterns of alien vertebrate species richness in mountain environments.

  2. The direction and magnitude of species flows between native and recipient realms influenced by various factors.

  3. The incidence of alien vertebrates in different types of protected areas within mountainous regions.

  4. The roles of anthropogenic pressures and mountain characteristics on alien vertebrate richness.

Global Patterns
Throughout the analysis, a total of 167,357 records of 717 alien vertebrate species were identified across 2978 mountains. Richness varied significantly, with some mountains hosting just 1 species while others, such as the Cairngorms in the UK, showed richness levels of 81 species. Notable hotspots identified for alien vertebrates include New Zealand, Reunion Island, Canary Islands, and the Lesser Antilles. The record density was observed to peak in northern temperate latitudes, with additional peaks in subtropical regions. Interestingly, fishes, amphibians, and reptiles are less represented compared to birds and mammals in mountain records, indicating an imbalance in the types of alien species that occupy these environments.

Species Flow Patterns
The patterns of species flow were predominantly influenced by contributions from the Nearctic, Indo-Malay, and Afrotropic donors, with Palearctic, Nearctic, and Australasian regions serving as recipients. Specific patterns varied across taxonomic groups:

  • Fishes: Major donors were identified as Nearctic and Afrotropic sources, with Nearctic and Palearctic regions functioning as recipients.

  • Birds and Reptiles: Main flows were observed moving from Afrotropic and Indo-Malay realms to Nearctic and Palearctic regions.

  • Mammals: The Indo-Malay and Palearctic realms acted as donors, while Australasian and Palearctic regions served as recipients.

Alien Vertebrates in Protected Areas
Within protected areas (PAs) across various mountain ranges, 347 species were reported, predominantly comprising birds and mammals. A significant number of records were found within Protected Landscapes and National Parks, emphasizing these areas' role in conservation. In contrast, Strict Nature Reserves exhibited the least records, suggesting that higher accessibility for human activities in certain protected areas may influence species distributions negatively.

Drivers of Alien Richness
The research identified both positive and negative drivers affecting alien vertebrate richness:

  • Positive effects: Factors such as human population density, road density, sampling completeness, and terrain roughness were found to positively influence richness. Additionally, characteristics like a narrow elevation range, pyramid geometry, and rapid temperature change also enhanced species richness in certain contexts.

  • Negative effects: Conversely, higher biodiversity intactness, increased distance to urban centers, ports, and a larger elevation range displayed negative relationships with the richness of alien species.

Conclusion
The study underscores the urgent need for conservation efforts in mountainous regions to minimize the impacts of biological invasions and preserve the integrity of these ecosystems. A thorough understanding of human influences and resulting biodiversity changes is crucial for effectively protecting mountain ecosystems against ongoing and future threats.