dc.description.abstract |
New Zealand native species are being Iost despite substantial resource investment.
Conservation managers predominantly rely on pest eradication and targeting the
needs of keystone species to enhance native species survival. The success of these
management practices is dependent on two major assumptions. Firstly, eradicating
pests from isolated areas automatically benefits native species in those (and
neighbouring) areas. Secondly, the role as keystone species is an intrinsic quality.
The latter assumes that species perform the same function regardless of context or
individual differences amongst members within the same population. While pest
eradication and targeting the needs of keystones dominates conservation management
in New Zealand, there have been few (if any) studies challenging the validity of these
assumptions. This thesis addresses this research gap using kereru as a case study.
Kereru are frequently given conservation priority in New Zealand. This is due to their
assumed role as the sole surviving disperser of large fruited (>10mm in diameter)
plant species.
A comparative assessment of kereru response to pest management revealed that
intensive pest control in some areas does not necessarily benefit all kereru, Iet alone
those in neighbouring areas. Unmanaged sites have fewer kereru, no (or very little)
intra-specific competition, and greater quality food. However, these areas have stable
or declining kereru numbers that are determined by constraints on breeding. By
contrast, managed areas have more kereru, higher inter-specific competition, poorer
quality food, but dominants do well. In these areas, kereru populations increase until
they reach food limits, and population size is most likely to be constrained by
limitations on food resources.
The role of kereru does not appear to be an intrinsic quality. Contrary to widespread
assumptions, the function of kereru within the landscape appears to be heavily
governed by context. Kereru in unmanaged areas appear to contribute to poorer
seedling recruitment success. This is because lower numbers of kereru in these areas
results in kereru exhibiting a tendency towards: 1) a narrower diet; 2) slower and
irregular movement patterns; 3) use of a smaller number of species during a foraging
bout; and 4) post foraging behaviour that results in: a) longer periods of inactivity on
the same fruiting tree; or (alternatively) movement onto b) con-specifics; or c)
movements back onto preferred fruiting trees. Consequently, while kereru in these
areas have the morphological and physiological traits of a high quality seed disperser,
it appears that they are contributing to seed limitation rather than enhancing seedling
recruitment success.
The magnitude of these differences is heavily moderated by differences in plant
reproductive strategies. The abundance of kereru is unlikely to govern the degree to
which they disperse smaller fruited (<10mm in diameter) plant species. This is
because these species present fruit in such a way that increases the likelihood that
kereru will make foraging and post-foraging movements regardless of the number of
kereru in an area. By comparison, the abundance of kereru in an area is a strong
predictor of their seed disperser potential for larger fruited (>10mm in diameter) plant
species. This is because kereru are only likely to make foraging and post-foraging
movements from these species in areas where kereru abundance is relatively high.
An evaluation of the role of different kereru within the same population suggested
that non-breeding individuals exhibit greater seed disperser potential than their
breeding counterparts. This is because non-breeding individuals exhibited: 1) Iess site
tenacity; 2) greater dispersal; 3) larger home ranges; 4) larger feeding areas; and 5)
utilised a greater number of feeding nuclei.
Consequently, it is not only wrong for managers to assume that kereru perform the
same role in different management contexts. It is also wrong to assume that
individuals within the same population perform the same role. Indeed, it is likely that
the same individual performs a different function in different parts of the landscape,
and even within the same landscape over space and time.
These findings were confirmed via a meta-anaIysis of 32,284-minute focal
observations of kereru behaviour and seed dispersal potential in managed and
Unmanaged areas, north of Auckland. In order to achieve this objective, data chapters
considered kereru: 1) treatment of seed; and 2) foraging behaviour; as well as 3) the
probability of kereru moving seed to suitable sites for seedling recruitment success.
The latter was determined by a cumulative calculation of: 1) the number of fruit
consumed per foraging bout; 2) gut passage times; 3) the time and location from
which foraging and post-foraging movement occurred; and 4) the spatial location (or
biotic neighbourhood) to which movements occurred.
The Iast part of this thesis uses The Natural Step (TNS) hierarchical decision-making
framework to: 1) identity causal mechanisms underpinning management failure; and
2) develop management guidelines to assist managers in achieving desired
management outcomes. A sustainability gap analysis revealed that current
management appears to have no principles for success. Emphasis is placed on actions
without having bounded strategies that will enhance the success of those actions. In
turn, these failings remain largely unrecognised because of a paucity of tools to
measure success. This suggests that there is an urgent need for conservation tools to
measure success and a clear need for a declared vision so that all can participate.
In summary, managers should not assume that contemporary management practices
will always achieve desired outcomes. Adopting a hierarchical decision-making
framework could provide a better assessment of current management; help create the
vision; and develop a strategic plan of action that could be updated as a mechanism to
enhance management. These approaches will better reflect the needs of people and
the environment. |
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