For many species, distribution and abundance is driven by a trade-off between abiotic and
biotic stress tolerance (i.e. physical stress versus competition or predation stress). This trade-
off may be caused by metabolic rate differences in species such that slow metabolic rates
increase abiotic tolerance but decrease biotic tolerance. I investigated how metabolic rate
differences were responsible for an abiotic-biotic tolerance trade-off in brown mudfish
(Neochanna apoda) and banded kokopu (Galaxias fasciatus), that drives the allopatric
distribution of these fish in podocarp swamp-forest pools. Brown mudfish and banded
kokopu distribution across 65 forest pools in Saltwater forest, Westland National Park, New
Zealand was almost completely allopatric. Mudfish were restricted to pools with extreme
abiotic stress including hypoxia, acidity and droughts because of kokopu predation in benign
pools. This meant the mudfish realised niche was only a small fraction of their large
fundamental niche, which was the largest out of sixteen freshwater fish species surveyed in
South Island West Coast habitats. Thus mudfish had a large fundamental to realised niche
ratio because of strong physiological stress tolerance but poor biotic stress tolerance
compared to other fish. A low metabolic capacity in mudfish compared to kokopu in terms of
resting and maximum metabolic rates and aerobic scope explained the strong mudfish
tolerance to extreme abiotic stress, but also their sensitivity to biotic stress by more powerful
kokopu in benign pools, and hence their allopatric distribution with kokopu. Despite being
restricted to extreme physical stress, mudfish populations were, in fact, more dense than those
of kokopu, because of low individual mudfish resting metabolic rates, which would cause
resources to be divided over more individuals. Distribution and abundance in mudfish and
kokopu were therefore driven by an abiotic-biotic tolerance trade-off caused by a
physiological trade-off between having slow or fast metabolic rates, respectively. The negative relationship between species resting metabolic rates and their tolerance to abiotic
stress provides a way of estimating the impact of human induced environmental change that
can either increase or decrease habitat harshness. Thus species with low metabolic rates, like
mudfish, will be negatively affected by human induced environmental change that removes
abiotic habitat stress and replaces it with benign conditions. My evidence shows that extreme
stressors provide a protective habitat supporting high mudfish biomass with significant
conservation value that should be maintained for the long-term persistence of mudfish
populations.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/8011 |
| Date | January 2013 |
| Creators | White, Richard Stuart Alan |
| Publisher | University of Canterbury. Biological Sciences |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Richard Stuart Alan White, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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