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

Thesis (MSc)--Stellenbosch University, 2014.

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.

AFRIKAANSE OPSOMMING: Uitheemse indringerplante is verantwoordelik vir verskeie veranderinge in natuurlike habitatte wat verdere impak op die geassosieerde inheemse diergemeenskappe totgevolg het. Studies oor die effek wat uitheemse indringerplante op akkedis spesiesamestelling het is beperk, veral die effek van Radiataden, Pinus radiata. Die doel van die studie was om die effek van P. radiata op akkedis spesiesamestelling en die gepaardgaande termiese landskap en beskikbaarheid van prooi in inheemse berg fynbos, fynbos wat intermediêr ingedring word deur dennebome en denneboom woude, in die Wes-Kaap te bepaal. Akkedis-opnames is in beide Jonkershoek Natuurreservaat en die Witzenberg Bergreeks gedoen om spesierykheid, volopheid en diversiteit te ondersoek. Die termiese landskap van elke habitat is gemeet deur middel van operatiewe temperatuur modelle wat in oop en toe blaardak omgewings geplaas is. Verder het ek beskikbaarheid van prooi in die verskillende habitat tipes ondersoek deur die gebruik van ‘n verskeidenheid aanvullende metodes. Akkedis spesierykheid, volopheid en diversiteit was hoër in die meer komplekse fynbos habitat as in die struktureel eenvoudiger denneboom woud. Langs die indringer gradient het fynbos met ‘n lae voorkoms van dennebome ‘n hoër akkedis spesierykheid, volopheid en diversiteit gehad as fynbos met ‘n hoër voorkoms van dennebome. Nietemien, fynbos met ‘n hoër voorkoms van dennebome het die laagste akkedis diversiteit van al die habitat tipes gehad. Daar was duidelike verskille in die habitat struktuur tussen al die habitat tipes, in beide studie areas, en dit het ‘n direkte impak op die termiese landskap gehad. In altwee studie areas het temperature wat in oop en toe blaardak omgewings opgeneem is ‘n reeks temperature verteenwoordig wat deur akkedis families van die Wes-Kaap geteiken word, wat termoregulering geleenthede vir akkedisse bied. Vir altwee studie areas, het oop en toe blaardak omgewings in die denneboom woud selde temperature bereik wat in die reeks van voorkeur ligaamstemperature val tipies vir hierdie spesies. Operatiewe temperature in die denneboom woud was die mees gebuffer, met die kleinste reeks van gunstige temperature. Fynbos en intermediêr ingedringde fynbos was termies meer heterogeen as denneboom woude, wat akkedisse ‘n groter verskeidenheid van bak geleenthede bied. Geleedpotige volopheid en samestelling het n soortgelyke tendens as die akkedis spesiesamestelling gevolg, waar die kwantiteit en kwaliteit van prooi gewissel het oor verskillende habitat tipes. Denneboom woude het die laagste volopheid van prooi in beide studie areas gehad. Hierdie studie toon die effekt van denneboom woude en gepaardgaande indringers op inheemse akkedis spesiesamestellings en beklemtoon die belangrikheid van ‘n hoë kwaliteit termiesie landskap om akkedis volopheid en diversiteit te onderhou. Ek stel voor dat in areas waar Pinus radiata besig is om inheemse fynbos in te dring, akkedis spesiesamestellings benadeel sal word deur die vinnige vervanging van inheemse habitat deur ‘n suboptimale omgewing, saamgestel uit ‘n veranderde habitat struktuur, verlaagde termiesie kwaliteit en verminderde voedsel hulpbronne.