Native and adventive detritivores in forests of Manawatu-Whanganui : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology at Massey University, Manawatu, New Zealand
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Date
2013
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Massey University
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Abstract
Little is known about many New Zealand invertebrates, including detritivores which
have a key role in the functioning of ecosystems and are threatened by habitat
modification and the addition of adventive species. Detritivores are an abundant
group, and, like many other New Zealand taxa, they contain a high level of endemism
that needs conserving. Detritivores are so scarcely studied, that it remains unknown
how their forest communities are influenced by changes to New Zealand’s forest
habitats. This study aimed to increase knowledge on the identity, abundance, and
distribution of detritivores in forests of Manawatu-Whanganui. Four main questions
were addressed: (1) are adventive detritivores capable of invading native forests?, (2)
can pine forests provide an alternative forest habitat for native detritivores?, (3) does
proximity to forest edge affect native and adventive detritivores?, (4) are native and
adventive detritivores co-occurring in the same habitats? Three detritivore groups
(Diplopoda, Isopoda, and Amphipoda) were collected from edge and centre plots in six
pine forests and ten native forests (including those that are small and close to urban
areas) in Manawatu-Whanganui region of New Zealand.
The results show that a number of adventive taxa have spread throughout
native forests in Manawatu-Whanganui, which does not support the hypothesis that
native forests are resistant to adventive detritivores. Adventive Diplopoda were
actually more abundant in native forests, and abundance of adventive Amphipoda and
adventive Isopoda was high in both native and pine forests. Some native taxa were
less dominant or absent in pine forests, and forest type influenced the community
structure of Diplopoda and possibly Isopoda. The likelihood that a randomly collected detritivore would be an adventive was also influenced by forest type in all three
detritivore groups. Human disturbance may have facilitated the invasion and
establishment of adventive species, because small, urban, and highly modified native
remnants appeared to have higher abundance and diversity of adventive species. Edge
proximity had little influence on abundance of detritivores, but did affect the predicted
likelihood of encountering an adventive individual in all three groups.
Adventive and native detritivores co-occurred in all forest habitats and it is
possible that adventive detritivores will be influencing native species. Native
Amphipoda appear to be under the most immediate threat in Manawatu-Whanganui,
with adventive Amphipoda having higher abundance and higher probability of being
found throughout all investigated forest habitats; there is evidence that adventive
Arcitalitrus is displacing native species. The presence of adventive species could alter
the functioning of native forest ecosystems and further research into the effect of
adventive species in native forest is recommended. The data also revealed that for all
three investigated taxa pine forests can support as many native detritivores as native
forests, suggesting that pine forests contribute to preserving native biodiversity. Pine
forests may be used as a tool to conserve native detritivores, but the conditions which
promote the establishment of native species need further investigation.
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Keywords
Invertebrates, Detritivores, Detritus, Manawatu-Wanganui, New Zealand