Using experimental reintroductions to resolve the roles of habitat quality and metapopulation dynamics on patch occupancy in fragmented landscapes.

Declines of species in fragmented landscapes can potentially be reversed either by restoring connectivity or restoring local habitat quality. Models fitted to snapshot occupancy data can be used to predict the effectiveness of these actions. However, such inferences can be misleading if the reliability of the habitat and landscape metrics used is unknown. The only way to unambiguously resolve the roles of habitat quality and metapopulation dynamics is to conduct experimental reintroductions to unoccupied patches so that habitat quality can be measured directly from data on vital rates. We, therefore, conducted a 15-year study that involved reintroducing a threatened New Zealand bird to unoccupied forest fragments to obtain reliable data on their habitat quality and reassess initial inferences made by modeling occupancy against habitat and landscape metrics. Although reproductive rates were similar among fragments, subtle differences in adult survival rates resulted in λ (finite rate of increase) estimations of <0.9 for 9 of the 12 fragments that were previously unoccupied. This was the case for only 1 of 14 naturally occupied fragments. This variation in λ largely explained the original occupancy pattern, reversing our original conclusion from occupancy modeling that this occupancy pattern was isolation driven and suggesting that it would be detrimental to increase connectivity without improving local habitat quality. These results illustrate that inferences from snapshot occupancy should be treated with caution and subjected to testing through experimental reintroductions in selected model systems.

Uso de Reintroducciones Experimentales para Determinar las Funciones de la Calidad delHábitat y las Dinámicas Metapoblacionales en la Ocupación de Paisajes Fragmentados Resumen La declinación de las especies en paisajes fragmentados tiene el potencial de ser revertida mediante la restauración de la conectividad o de la calidad del hábitat. Se pueden utilizar los modelos ajustados a los datos de ocupación instantánea para predecir la efectividad de estas acciones. Sin embargo, estas inferencias pueden ser engañosas si se desconoce la confiabilidad de las medidas usadas para el hábitat y el paisaje. La única manera de determinar inequívocamente las funciones de la calidad del hábitat y de las dinámicas metapoblacionales es mediante la realización de reintroducciones experimentales en los fragmentos no ocupados, de tal manera que se puede medir directamente la calidad del hábitat a partir de los datos de las tasas vitales. Por lo tanto, realizamos un estudio de 15 años que involucró la reintroducción de un ave neozelandesa amenazada en fragmentos no ocupados de bosque para así obtener datos confiables de la calidad del hábitat y reevaluar las inferencias iniciales hechas por los modelos de ocupación en relación con las medidas de hábitat y paisaje. Aunque las tasas de reproducción fueron similares entre los fragmentos, algunas diferencias sutiles en las tasas de supervivencia de los adultos resultaron en estimaciones λ (una tasa finita de incremento) <0.9 en nueve de los doce fragmentos que no estaban ocupados previamente. Este fue el caso para uno solo de los 14 fragmentos ocupados naturalmente. Esta variación λ explicó en su mayoría el patrón original de ocupación, revirtiendo nuestra conclusión original obtenida del modelo de ocupación de que este patrón estuvo causado por el aislamiento y sugiriendo que sería perjudicial incrementar la conectividad sin mejorar la calidad del hábitat local. Estos resultados muestran que las inferencias a partir de la ocupación instantánea deberían abordarse con cautela y estar sujetas al análisis mediante reintroducciones experimentales en sistemas modelados selectos.

Demographic rates of northern royal albatross at Taiaroa Head, New Zealand.

Demographic rates, such as annual survival rate, are generally difficult to estimate for long-lived seabirds, because of the length of time required for this kind of study and the remoteness of colonies. However, a small colony of northern royal albatross (Diomedea sanfordi) established itself on the mainland of New Zealand at Taiaroa Head, making possible regular banding and monitoring of its individuals since the first chick fledged, in 1938. Data on the presence/absence of birds, as well as on breeding outcomes, were available for the period from 1989-90 to 2011-12, and included 2128 annual resightings of 355 banded individuals of known age. The main goal of the present study was to estimate the annual survival rate of juveniles, pre-breeders, and adults at Taiaroa Head. These rates were estimated simultaneously in a single Bayesian multi-state capture-recapture model. Several models were fitted to the data, with different levels of complexity. From the most parsimonious model, the overall annual adult survival rate was estimated as 0.950 (95% CI [0.941-0.959]). In this model, adult survival declined with age, from 0.976 (95% CI [0.963-0.988]) at 6 years, the minimum age at first breeding, to 0.915 (95% CI [0.879-0.946]) at 40 years. Mean annual survival of pre-breeders was 0.966 (95% CI [0.950-0.980]), and 0.933 (95% CI [0.908-0.966]) for juveniles. There was no discernible difference in survival between males and females, and there was no apparent trend in survival over time. Estimates of other demographic rates were also obtained during the estimation process. The mean age at first return of juveniles to the colony was estimated as 4.8 years (95% CI [4.6-5.1]), and the mean age at first breeding as 8.9 years (95% CI [8.5-9.3]). Because all the birds of the colony were banded, it was possible to estimate the total population size. The number of northern royal albatross present annually at the Taiaroa Head colony has doubled since 1989-90, and the current total population size was estimated to be over 200 individuals. The ratio of the total population size to the number of annual breeding pairs varied from 5 to 12 among years, with an overall mean of 7.65 (95% CI [7.56-7.78]), and this high variability highlights the need for a sufficient number of surveys of seabird breeding populations before reliable conclusions on population trends can be made. Although long-term data allowed estimates of demographic rates of northern royal albatross at Taiaroa Head, the location of the colony and the ongoing management by staff mean that the population dynamics may differ from those of the main population on the Chatham Islands.

Strategic rat control for restoring populations of native species in forest fragments.

Forest fragments have biodiversity value that may be enhanced through management such as control of non-native predators. However, such efforts may be ineffective, and research is needed to ensure that predator control is done strategically. We used Bayesian hierarchical modeling to estimate fragment-specific effects of experimental rat control on a native species targeted for recovery in a New Zealand pastoral landscape. The experiment was a modified BACI (before-after-control-impact) design conducted over 6 years in 19 forest fragments with low-density subpopulations of North Island Robins (Petroica longipes). The aim was to identify individual fragments that not only showed clear benefits of rat control, but also would have a high probability of subpopulation growth even if they were the only fragment managed. We collected data on fecundity, adult and juvenile survival, and juvenile emigration, and modeled the data in an integrated framework to estimate the expected annual growth rate (λ) of each subpopulation with and without rat control. Without emigration, subpopulation growth was estimated as marginal (λ = 0.95-1.05) or negative (λ = 0.74-0.90) without rat control, but it was estimated as positive in all fragments (λ = 1.4-2.1) if rats were controlled. This reflected a 150% average increase in fecundity and 45% average increase in adult female survival. The probability of a juvenile remaining in its natal fragment was 0.37 on average, but varied with fragment connectivity. With juvenile emigration added, 6 fragments were estimated to have a high (>0.8) probability of being self-sustaining (λ > 1) with rat control. The key factors affecting subpopulation growth rates under rat control were low connectivity and stock fencing because these factors were associated with lower juvenile emigration and higher fecundity, respectively. However, there was also substantial random variation in adult survival among fragments, illustrating the importance of hierarchical modeling for fragmentation studies.

Sampling optimization for printer characterization by greedy search.

Printer color characterization, e.g., in the form of an ICC output profile or other proprietary mechanism linking printer RGB/CMYK inputs to resulting colorimetry, is fundamental to a printing system delivering output that is acceptable to its recipients. Due to the inherently nonlinear and complex relationship between a printing system's inputs and the resulting color output, color characterization typically requires a large sample of printer inputs (e.g., RGB/CMYK) and corresponding color measurements of printed output. Simple sampling techniques here lead to inefficiency and a low return for increases in sampling density. While effective solutions have been proposed to this problem very recently, they either do not exploit the full possibilities of the 3-D/4-D space being sampled or they make assumptions about the underlying relationship being sampled . The approach presented here does not make assumptions beyond those inherent in the subsequent tessellation and interpolation applied to the resulting samples. Instead, the tradeoff here is the great computational cost of the initial optimization, which, however, only needs to be performed during the printing system's engineering and is transparent to its end users. Results show a significant reduction in the number of samples needed to match a given level of color accuracy.