|dc.description.abstract||The invasion of non-indigenous species is considered to be one of the leading causes of biodiversity loss globally. My research aimed to determine if constructed water bodies (e.g., water supply reservoirs, dams and ponds) were invaded by zooplankton with greater ease than natural water bodies, and whether this was due to a lower biodiversity, and therefore lower 'biotic resistance', in constructed water bodies. Sediment cores were collected from a cross-section of 46 lakes, ponds and reservoirs (23 natural and 23 constructed) throughout the North Island, New Zealand. Diapausing zooplankton eggs were separated from the sediments and hatched to assess species composition and richness. In addition, the distributions of non-indigenous zooplankton were examined to determine if they occurred more frequently in constructed water bodies than in natural ones.
Species composition results showed that natural water body zooplankton communities appeared to consist mainly of a core group of truly planktonic species. However, the species assemblages of constructed water bodies were more varied, comprising of a number of littoral and benthic species, and a large number of species that were recorded from only a single water body. A canonical correspondence analysis indicated that Trophic Level Index explained a significant amount of variation in zooplankton community composition of natural waters (p = 0.002). Distance to nearest water body and number of water bodies within a 20 km radius explained significant amounts of variation in community composition of constructed water bodies (p = 0.040 and 0.038 respectively). Average species richness was slightly higher for natural water bodies than constructed water bodies (18.47 and 15.05 respectively), although overall there was a lot of variation for both natural and constructed water body datasets. A stepwise linear regression indicated that latitude and approximate maximum depth of water body were significant predictors of natural water body species richness (p = 0.002 and 0.016 respectively). However, no significant predictors of species richness were elucidated for constructed water bodies. The non-indigenous calanoid copepods Sinodiaptomus valkanovi and Boeckella minuta were only found in constructed water bodies. However, the non-indigenous cladoceran Daphnia galeata was recorded in both natural and constructed water bodies. The non-indigenous calanoid copepods are more likely to establish populations in constructed water bodies due to the absence of key species (i.e. native calanoid copepods), whose presence in natural waters seemingly provides 'biotic resistance'. The invasion success of D. galeata in constructed and natural waters may be attributed to the absence of a superior competitor, as native Daphnia populations, for example, are rare in the North Island.
My results suggest that species richness may not be as important as species composition in influencing the ease with which non-indigenous species invade constructed water bodies. The core group of species found in natural water bodies are likely to be better adapted to pelagic conditions, and therefore better at resisting invaders, than the more varied constructed water body assemblages.||en_NZ