Impacts of alien invasive pine Pinus radiata on lizard diversity and thermal habitat quality

[摘要] ENGLISH ABSTRACT: Invasive alien plants are responsible for a wide range of changes in native habitats which have cascading effects on the associated native animal communities. Studies of the effects of invasive alien plants on lizard assemblages are limited, especially the effects of Monterey pine, Pinus radiata. The objective of this study was to assess the effects of P. radiata on lizard assemblages and their associated thermal landscape and prey availability in native mountain fynbos, intermediately invaded fynbos and pine forests, in the Western Cape. Lizards were surveyed in Jonkershoek Nature Reserve and Witzenberg Mountain Range to examine species richness, abundance and diversity. The thermal landscape of each habitat was measured using operative temperature models placed in open and closed canopy sites. Additionally, I examined the availability of prey across habitat types using a range of complementary methods. Lizard species richness, abundance and diversity were greater in the more complex fynbos habitats than in the structurally simpler pine plantations. Along the invasion gradient, semi-invaded fynbos was higher than heavily-invaded fynbos in richness, abundance and diversity of lizards. However, heavily-invaded fynbos had the lowest lizard diversity of all habitat types. Clear differences were shown in habitat structure across all habitat types in both locations, and these directly affected the associated thermal landscape. For both locations, open- and closed-canopy sites in fynbos and intermediately invaded sites represent temperatures targeted by the lizard families found within the Western Cape, providing lizards with the opportunity to thermoregulate. Pine forest open- and closed-canopy sites of both locations rarely reached temperatures that fall within the range of preferred body temperatures typical of these species. Operative temperatures in pine forest habitat were most buffered from temperature variation and had the smallest range of favourable temperatures. Fynbos and intermediately invaded fynbos sites are thermally more heterogeneous than pine forest, presenting lizards with a wider range of basking opportunities. Arthropod abundance and composition followed a similar trend to lizard assemblages, where the quantity and quality of prey varied across habitat types. Pine forest supported the lowest quantity of prey in both locations. This study demonstrates the effects of pine plantations and related invasions on native lizard assemblages and highlights the importance of high quality thermal landscapes to maintain lizard abundance and diversity. I suggest that in areas where Pinus radiata is invading native fynbos, lizard assemblages will be disadvantaged by the fast replacement of native habitat with a suboptimal environment composed of altered habitat structure, lowered thermal quality and reduced resources.

[发布机构] Stellenbosch University