Search Results

Author: DAVID SALTZ

Since the formulation of hypothesis testing by Neyman and Pearson in 1933, the approach has been subject to continuous criticism. Yet, until recently this criticism, for the most part, has gone unheeded. The negative appraisal focuses mainly on the fact that P-values provide no evidential support for either the null hypothesis (H0) or the alternative hypothesis (Ha). Although hypothesis testing done under tightly controlled conditions can provide some insight regarding the alternative hypothesis based on the uncertainty of H0, strictly speaking, this does not constitute evidence. More importantly, well controlled research environments rarely exist in field-centered sciences such as ecology. These problems are manifestly more acute in applied field sciences, such as conservation biology, that are expected to support decision making, often under crisis conditions. In conservation biology, the consequences of a Type II error are often far worse than a Type I error. The "advantage" afforded to H0 by setting the probability of committing a Type I error (α) to a low value (0.05), in effect, increases the probability of committing a Type II error, which can lead to disastrous practical consequences. In the past decade, multi-model inference using information-theoretic or Bayesian approaches have been offered as better alternatives. These techniques allow comparing a series of models on equal grounds. Using these approaches, it is unnecessary to select a single "best" model. Rather, the parameters needed for decision making can be averaged across all models, weighted according to the support accorded each model. Here, I present a hypothetical example of animal counts that suggest a possible population decline, and analyze the data using hypothesis testing and an information-theoretic approach. A comparison between the two approaches highlights the shortcomings of hypothesis testing and advantages of multi-model inference.

In: Israel Journal of Ecology and Evolution
Authors: Adiv Gal, David Saltz, and Uzi Motro

The effect of food supplement to Lesser Kestrel (Falco naumanni) nests during the nestling period (from hatching to fledging) was studied in two nesting colonies in Israel – Alona and Jerusalem. Our hypothesis, based on diminishing returns considerations, was that food supplement will have a greater effect on fledgling success in the food-limited, urban colony of Jerusalem, than in the rural colony of Alona. Indeed, food supplement had a significantly positive effect on breeding success in both colonies. However, and contrary to our prediction, the decrease in chick mortality between supplemented and control nests in Jerusalem was not larger than in Alona (actually it was numerically smaller, albeit not significantly so). This implies either that additional factors, possibly urbanization associated, other than food limitation, might be responsible for the difference in nesting success of Lesser Kestrels between Alona and Jerusalem, and/or that the amount or the nutritional quality of the additional food provided to supplemented nests (three mice per chick per week), was not enough.

In: Israel Journal of Ecology and Evolution

Golan wolves are smaller relative to most other populations, but are larger than the wolves found in the south of Israel. Pups are born from mid-February through March. Golan wolves produce an average of 5 pups per litter. In some cases the pups are moved from the den when they are two to three months old, while in other cases they stay in the den until they are five or six months old.In spite of the low survival rate (61%), the reproductive rate is high, and it appears that the population of the Golan wolves has increased in recent years. Population data show that the Golan area is saturated or almost saturated with wolf packs. The wolf population in the Golan is estimated at 80–100 adult wolves. The emigration rate of the Golan wolf to neighboring areas is low (9%) and dispersal distances are relatively short (15.6 km on average). The link between the Golan population and other populations outside the Golan reduces the sensitivity of the population to active management.

Their diet consists mainly of gazelles, young wild boars, carrion, and live-stock. In the southern part of the Golan, more than 50% of the wolves' diet is domestic animals (especially chicken carcasses).

A wolf's home range in the Golan averages 46 square kilometers and is small compared to wolves in other areas. The overlap with neighboring home ranges is low. Sometimes home ranges change over the years. A seasonal pattern could not be found. Golan wolves are mainly nocturnal and are rarely active more than two or three hours after sunrise. On winter nights there are two activity peaks, while during summer there is only one peak, in the early hours of the night. In the summer there is no wolf activity during the middle of the day, while in the winter there is some.

Resting sites during the day are not scattered randomly in the area, but concentrated in a small part of the home range. Even in winter, when the pack is not caring for pups, after foraging the wolves return to where they started from in 28% of cases. On average, the wolves traverse 9.1 km while foraging.

Packs consist of 2–7 individuals. The foraging group size of Golan wolves changes by season. It is more common for wolves to forage alone in summer than in other seasons. In winter, foraging groups are larger. In September, pups start joining the pack on its foraging journeys. At ten months of age, the pups start to forage alone. When they are one year old, some pups leave the pack and roam by themselves. Other pups stay with the pack and help in car-ing for the next generation.

Examination of the data in a demographic model shows that the wolf population in the Golan can sustain itself under heavy culling. However, because of the difficulty in long-term monitoring, careful consideration is needed in the desired management plan. To deter wolf predation, we recom-mend combining protection methods with the killing of wolves that learn how to overcome these protection procedures. In addition, we advise dividing the Golan into three management areas. Stressing the wolf population should be avoided in one of these areas, while in the other two it should be permissible at different levels, according to livestock predation rates and to other manage-ment needs of the

In: Israel Journal of Ecology and Evolution

Reintroduction of herbivores may play a vital role in restoring ecosystem functions. Here we describe the role of the Persian fallow deer (Dama mesopotamica), reintroduced into Israel, as a vector of seed dispersal by endozoochory. Persian fallow deer have a wide diet both from grazing and browsing. From fecal samples, we found that more than 30 species of plants germinated from the deer pellets. Four of the more common species are considered as ruderal. Of the trees, carob (Ceratonia siliqua) seeds were the only intact seeds found in the fecal samples. We found that ingestion by the deer has a positive effect on expediting the germination of carob seeds – a factor of ecological importance in the reintroduction environment, as it contributes to plant genetic diversity by long-range seed dispersal and to community diversity.

In: Israel Journal of Ecology and Evolution

We studied Lesser Kestrels’ (Falco naumanni) conditional nest-site fidelity, i.e., fidelity that depends on the outcome of the previous nesting attempt in that site. In particular, we were interested in examining whether individual kestrels practice a Win–Stay/Lose–Shift (WSLS) strategy towards their nest-sites; that is, does the tendency to use the same nest-site increase following a successful nesting season, but decrease following a failure. For that purpose, we documented the use of nest-sites by Lesser Kestrels and the breeding success in these sites during 1998–2003 in the city of Jerusalem (Israel). We found that while Lesser Kestrels do not practice WSLS strategy towards their nest-site, the males (but not the females) do so towards their sub-colony – they tend to stay in the same sub-colony if their nesting was successful, whereas they tend to migrate to a different sub-colony after failure. A possible explanation to this sexual difference in WSLS behavior can arise from the fact that changing a sub-colony entails a change of hunting area. The male, being the main food provider in the Lesser Kestrel, may be more sensitive to this opportunity.

In: Israel Journal of Ecology and Evolution

Roadkills are the major cause of mortality in some predator species, including endangered species, and are considered one of the causes for the marked decline of otter populations around the world during the last century. We collected all available records of otter (Lutra lutra) roadkills in Israel, and analyzed them in order to assess the role of roadkills in the decline of the otter population in Israel and to find ways in which otter road mortality might be reduced. We found a significant increase in otter road casualty over the last 3 decades. Based on general estimates of population size, we suggest that at least 5% of the otter population in Israel is killed on the roads each year. A seasonal pattern was found: 64% of otter roadkills occurred in winter and spring. There was a slight male bias ratio in fatalities (1.27:1). A majority of casualty records (57.1%, n = 63) were within 100 m of fresh water. Our findings suggest that roadkill has a significant impact on the otter population in Israel. Suitable bridge design, underpasses at favored crossing points, ledges in culverts and bridges to allow otters to walk through even at high flows, fencing to divert otters to a safe underpass, and reflectors and warning signs for motorists can all be used to reduce roadkills.

In: Israel Journal of Ecology and Evolution