Charles R. Todd

The treatment of uncertainty and the structure of the IUCN threatened species categories

The classification of species with respect to their conservation status using the IUCN criteria is an important process in many countries, providing a guide for setting conservation priorities. Recent advances have resulted in several approaches to dealing with uncertainty in data used to classify species. These methods demand an unambiguous and transparent logical structure for the criteria. We suggest some changes to the ways in which the criteria are represented that correct an unnecessary inconsistency and which may serve to avoid important errors when uncertainty in the data is considered explicitly.

Probabilistic classification rules for setting conservation priorities

Decision rule sets are used widely to classify the conservation status of species. These classifications are intended to approximate the relative degree of threat faced by different species. They are important because they play a role in setting conservation priorities. It is suggested that such rule sets should take into account estimates of the statistical distribution and confidence intervals reported for each of the parameters. Examples are provided for three threatened Australian plant species.

Lessons about extinction and translocation: models for eastern barred bandicoots (Perameles gunnii) at Woodlands Historic Park, Victoria, Australia

In 1998 the protected population of Perameles gunnii (eastern barred bandicoot) at Woodlands Historic Park, Victoria, Australia became functionally extinct following removals of individuals for translocation between 1994 and 1996. Population viability analysis and data collected whilst the population was in decline are used to explore the impact that these removals had on the decline of the P. gunnii population at Woodlands. Due to some ambiguities in the life history of P. gunnii at Woodlands, two structurally different population models were used. Explicitly including the removal of animals in the analysis indicates that there may be at least a three-fold increase in the risk of quasiextinction due to removals. In some scenarios, over 17% of the trajectories decrease to a level less than or equal to 10 females within the observed time period of the collapse of the population, that is by April 1998. The modelling approach identified a number of critical factors in the decline of the population, such as variation in survival rates. By representing the life history strategy using two alternate models, quantitative statements about the impact that removals had on the population decline at Woodlands are made. While removals probably contributed to the collapse of the population, removals were not the sole cause of population decline. The real reasons for decline remain unknown; however, it is likely to be closely linked to habitat decline, difficult environmental conditions and predation. If P. gunnii are reintroduced to Woodlands again, then the models presented here may help to develop management strategies to establish a self sustaining population, as well as exploring translocations options.

Generating unbiased correlated random survival rates for stochastic population models

Abstract A problem for population modellers in undertaking quantitative population viability analysis has been restricting survival rates to the unit interval and retaining the specified mean and standard deviation. In order to overcome this problem, we have developed a general method for generating correlated survival rates. The method consists of applying the transformation Φ x , the cumulative distribution function of the standard normal distribution, to suitably correlated normal variates X1, X2, …, Xk. The means, standard deviations and correlation coefficients of X1, X2, …, Xk are calculated so that the transformed results have the desired means, standard deviations and correlations for the survival rates. This method allows the full spectrum of correlations among different ages/stages to be considered, as well as the flexibility of a range of differently shaped distributions. The method proposed may generally apply to any function that satisfies the definition of a cumulative distribution function for which a derivative and inverse exist. A case study using the Φ x transform exemplifies these advantages, especially in comparison with the typical process of limiting random deviates to the unit interval currently in use. The case study emphasises the point that the limiting of random deviates may lead to an under-estimation of the specified variation and, as a result, simulated risk curves exhibiting a smaller range in possible outcomes compared with our method. This has particular importance when developing population viability analysis models to assess the risk of extinction or quasiextinction of a population.

Recovery of the endangered trout cod, Maccullochella macquariensis: what have we achieved in more than 25 years?

Recovery of threatened species is often necessarily a long-term process. The present paper details the progress towards the recovery of trout cod, Maccullochella macquariensis, an iconic, long-lived fish species first listed as threatened in the 1980s. The objectives, actions and progress over three successive national recovery plans (spanning 18 years) are assessed, documenting changes to population distribution and abundance and updating ecological knowledge. Increased knowledge (especially breeding biology and hatchery techniques, movements, habitats and genetics) has greatly influenced recovery actions and the use of a population model was developed to assist with management options and stocking regimes. Key recovery actions include stocking of hatchery-produced fish to establish new populations, regulations on angling (including closures), education (particularly identification from the closely related Murray cod, M. peelii) and habitat rehabilitation (especially re-instatement of structural woody habitats). In particular, the establishment of new populations using hatchery stocking has been a successful action. The importance of a coordinated long-term approach is emphasised and, although there is uncertainty in ongoing resourcing of the recovery program, much has been achieved and there is cautious optimism for the future of this species.

Structural uncertainty in stochastic population models: delayed development in the eastern barred bandicoot, Perameles gunnii

Uncertainty about which model structure best describes the life history of a species may be a problem for the development of some population viability analysis (PVA). This paper describes the development and exploration of two structurally different stochastic population models when there is uncertainty about the life history of a species. Delayed reproduction was observed in a protected population of the small marsupial Perameles gunnii (eastern barred bandicoot) at Woodlands Historic Park, Victoria, Australia. This previously undocumented feature of P. gunnii may be considered to be either a component of the seasonal breeding cycle or it may be delayed development to sexual maturity. A delayed development model is compared to a standard development model where the parameter estimates of each model were obtained from a long-term mark-recapture study at Woodlands Historic Park. While the growth rate of the delayed development model is less than that of the standard model, the predicted risks of extinction/quasiextinction were higher for the standard model. This discrepancy is the result of different interpretations placed upon the available data underpinning the two models, the most important of which is the difference between the estimated variance in survivorship of the sub-adult stage. The results highlight the need for conservation assessments based on stochastic modelling to explore the degree to which the predicted extinction risk is affected by the incomplete knowledge of the species’ basic biology and parameter values.

Reintroduction success of threatened Australian trout cod (Maccullochella macquariensis) based on growth and reproduction

Internationally, re-introductions of endangered species into their former ranges have largely failed. Here we assess a successful reintroduction program of the endangered trout cod (Maccullochella macquariensis) and examine factors contributing to this success. Stocking of marked fish (all stocked fish were marked) occurred between 1997 and 2006 in the Ovens River, south-eastern Australia, where trout cod were historically abundant but locally extinct by the 1980s. We found no natural recruits (i.e. from spawnings of stocked fish in the wild) over the age of six, indicating that natural recruitment started at most five years after stocking began. Of the 83 fish we examined for sexual maturity, 12 were immature, 20 were male, and 51 were female. The body length at which 50% of the population can be considered mature was 325 and 250 mm for females and males, respectively. The length at which 90% of the population was mature was 394 and 318 mm for females and males, respectively. The smallest mature female was 245 mm. Average relative fertility was 9 eggs g–1 fish weight. The results we obtained provide valuable insights into the aspects contributing to the success of reintroduction programs for endangered freshwater species.

Collaborative Learning as Part of Adaptive Management of Forests Affected by Deer

Adaptive management requires the merger of management with science to provide robust knowledge about the effect of management actions. It can also be applied as a model of collaborative learning to support effective resource management. Using the example of adaptive management of native forests affected by introduced deer in New Zealand, we set out to identify some of the tensions that become apparent when adaptive management is applied in this way. We describe the process of adaptive management as it was applied in this case study. Drawing from project documentation and participant reflections on the learning process, we highlight three key lessons: (1) the need to create ‘space’ – i.e. a permissive environment that allows for an evolving process rather than a formalised and legalistic one; (2) that adaptive management cannot be expected to progress in a standardised way but instead, role clarity will emerge over time and this will contribute to an emerging vision of contribution that participants see for their project; and (3) the collaborative learning component of adaptive management poses a new challenge for science as rather than providing solutions to management issues, scientists contribute technical expertise and methods as part of the management

Short communication: Commentary: IUCN classifications under uncertainty

We comment on a recent article by Newton (Environ. Model. Softw. (2010), 25, 15-23), which proposed a method, based on a Bayesian belief networks, for classifying the threat status of species under the IUCN Red List Categories and Criteria, and compared this method to an earlier one that we had developed that is based on fuzzy logic. There are three types of differences between the results of the two methods, the most consequential of which is different threat status categories assigned to some species for which the input data were uncertain. We demonstrate that the results obtained using the fuzzy logic approach are consistent with IUCN Red List criteria and guidelines. The application of Bayesian Networks to the IUCN Red List criteria to assist uncertain risk assessments may yet have merit. However, in order to be consistent with IUCN Red List assessments, applications of Bayesian approaches to actual Red List assessments would need an explicit and objective method for assigning likelihoods based on uncertain data.

A management experiment reveals the difficulty of altering seedling growth and palatable plant biomass by culling invasive deer

Abstract Context. There is concern that deer are shifting forests towards undesirable trajectories, and culling of deer is often advocated to mitigate these impacts. However, culling deer is expensive and sometimes controversial. To reliably ascertain whether such action is beneficial, management-scale experiments are needed. We conducted a management experiment to evaluate the benefits of culling deer in four New Zealand forests. Aims. Our experiment tested the predictions that culling deer should increase (1) canopy tree seedling height relative growth rate (SHRGR), and (2) the foliar biomass of understorey species palatable to deer (FBP). Methods. Each forest was divided into two 3600-ha areas, with deer culling randomly assigned to one area. Deer abundances were indexed using faecal pellet counts, and forest variables were measured at the start and end of the 8-year experiment. Deer were already at low abundance in one forest and were not culled there. We used structural equation modelling (SEM) with Bayesian variable selection to update our a priori graphical forest–deer model with data from all four forests. Key results. Deer abundances were significantly reduced in one forest but increased or did not change in the other two forests in which deer culling occurred. Culling deer did not increase seedling height relative growth rate (SHRGR) or the foliar biomass of understorey species palatable to deer (FBP) in the three areas subject to deer culling compared with the three areas not subject to deer culling. SEM revealed no significant relationships between local-scale deer abundance and either SHRGR or FBP. Rather, tree basal area and the foliar biomass of unpalatable understorey species were important predictors of FBP and SHRGR, respectively, in some forests. Conclusions. Our study revealed that culling deer, as currently practiced by New Zealand land managers, did not generate the desired responses in New Zealand forests, possibly due to deer not being culled to sufficiently low densities and/or because forest dynamics and abiotic drivers determined plant growth more than deer. Implications. Managers should consider actions other than ineffective deer culling (e.g. creating canopy gaps) to alter the dynamics of New Zealand forests. Alternatively, managers will need to substantially increase culling effort above what is currently practised for this activity to substantially reduce deer populations and thus potentially alter forest dynamics.