Sol Brand

Geographical Ecology of Gerbilline Rodents in Sand Dune Habitats of Israel

In Israel, sand dune habitats of varying sizes occur along a rainfall gradient ranging from 30 to 650 m. In these sand dunes, nine species of granivorous rodents are found, eight of which belong to the family Gerbillidae. Rodent species were sampled during the four main seasons in eleven different locations covering the major sand dune habitats. Both species and their equivalent biomass were highly and significantly correlated with the mean annual rainfall. As the amount of rainfall increased, so did the number of species and their equivalent biomass. However, once a certain amount of rainfall was reached, an additional increase in rainfall was followed by a decrease in species number and biomass. Mean annual rainfall was similarly correlated with % annual cover, an index of the size of the seed crop on which the rodents feed. Number of rodent species was also significantly correlated with the area of the sand dune habitats. Analysis suggests that both rainfall and area are important in determining species number. Most of the patterns of community structure found in Israel are similar to those reported for the rodents that occur in the sand dunes of the desert of the western U.S.A.

Porcupine disturbances and vegetation pattern along a resource gradient in a desert

SummaryIn the Negev Desert, Israel, the Indian crested porcupine, Hystrix indica, digs similar sized, discrete, elongated pits (257±21.3 cm3; n=144) while foraging for below-ground plant storage organs. In these digs, soil moisture content is higher than in the surrounding soil matrix. The digs disturb population and community structure due to porcupine consumption or damage of 18 species of plants, and repopulation by 55 plant species. Over the past 14 years we have studied dig dynamics on a rocky hillslope with three distinct habitats as regards soil moisture content. Midslope soil moisture is the highest, decreasing towards upper and lower slope. We have counted a total of 6,609 digs in the area: 2141 on the upper, 3211 in the middle and 1257 on the lower part of the slope. The number of digs at midslope is significantly higher than on the other parts of the slope (ANOVA; P<0.0001). There is a significant (P<0.05) correlation between the mean number of porcupine digs and the cumulative rainfall amount for the 2 years prior to dig formation. To study plant repopulation in digs, all plants in 144 digs along the slope and from equal sized plots in the undistarbed soil matrix were collected. In all, 288 samples with 20 584 plants were collected, 2042 from the matrix and 18,542 from digs. Of the 55 species, we focused on the abundance patterns of Filago desertorum, Picris cyanocarpa and Bromus rubens, which made up 69.5% of all the individuals in the digs and 68.3% in the matrix. Our results showed that all three species increased in abundance in the digs as compared to the matrix. F. desertorum density increased by a factor of 2.9, P. cyanocarpa by 9.5 and B. rubens by 12.0. There were species-specific responses in abundance to the location of the digs along the moisture gradient. The only species whose abundance responded to the moisture gradient was F. desertorum. P. cyanocarpa demonstrated peak abundance in the location with the poorest moisture regime, while B. rubens showed peak abundance at the intermediate part of the moisture gradient. We suggest a scheme for integrating the increase in density and the species-specific responses to the digs along a water gradient based on R.H. Whittakers view of individual species abundances along an environmental gradient.

The relationship between sit and wait foraging strategy and dispersal in the desert scorpion, Scorpio maurus palmatus

We examine the role of the sit and wait foraging strategy and of the stability and predictability of the biotic environment in shaping population biology and life history traits of the desert scorpion, Scorpio maurus palmatus. The study was carried out in a loessial plain in the Negev desert, Israel. We used a grid system (5x80 m) within the Hammada scoparia plant association. The area was divided into 1,600 squares (50x50 cm) and the presence (within ±5 cm) and width of each scorpion burrow was recorded for eight years (1973–1980). It was found that: (1) Dispersal is a common phenomenon for all S. maurus palmatus age groups and takes place only after a heavy rainfall when soil moisture is high. (2) Dispersion patterns change from clumped to random as a function of age. (3) Dispersal is age specific and density dependent. (4) During the dry seasons a high percentage of the population goes into the resting stage.In order to integrate the above findings, a graphical model was constructed with the main assumption that the S. maurus palmatus prey availability relationship is a decreasing function between the scorpion burrow and its food resources. Data and model analysis led to the conclusion that the desert scorpion, S. maurus palmatus, is confronted with a relatively predictable physical environmeent and unpredictable biological environment. Two alternative strategies are available for S. maurus palmatus to overcome prey unpredictability; dispersal during the rainy season and inactivity during the dry seasons.We suggest that many other burrowing desert animals may face the problem of unpredictability of biological resources. Thus it seems that the S. maurus palmatus biological relationship model can be applied, with modifications, to a wide spectrum of desert burrowing animals.

Relations Among Spatiotemporal Heterogeneity, Population Abundance, and Variability in a Desert

There are at least two features of natural systems that ecologists agree on: (1) they are abiotically heterogeneous in time and space; and (2) they are variable in organism abundance (e.g., Sousa, 1984). In the literature there are discrepancies as to the usage of the terms heterogeneity and variability (see Chapter 1); therefore we define our usage of the terms. Heterogeneity refers to composition of parts of different kinds, and variability indicates changes in values of one kind (Random House Dictionary).

Predation by rodents and the distribution and abundance of the snail Trochoidea seetzenii in the Central Negev Desert of Israel

The desert snail Trochoidea seetzenii exhibits a regular pattern of spatial distribution in the Central Negev drainage basin : high density at the wadi bottom, gradually decreased density toward the top, and very low density at the hill tops. This pattern might be the result of increasing predation pressure by rodent species along the slope (...) To test the hypothesis that predators limit the distribution of rodents along the slopes, we constructed artificial shelters along an entire slope (...) We also collected data from a long term manipulation of shelters (27 yr) and found that the snail density is significantly and drastically reduced relative to a control plot. Snail density along the hillside is also correlated with the number of shrubs and the availability of egg laying sites. Predation, shrubs, and laying sites determine the basic distribution pattern of the snails in the area

Relationship among settling, demography and habitat selection: an approach and a case study

SummaryWe explore the demographic consequences of site selection by animals on their abundance among habitats. We found that pre and post settling survivorship are important links between the behavioral decisions where to settle and the distribution of a population among habitats. This was demonstrated for 10 generations of the desert isopod, Hemilepistus reaumuri, in three habitats in the Negev Desert, Israel. The populations exhibit low survivorship before settling (≈12%) and high survivorship (≈55%) after settling. According to our model this implies high site selection. Theoretical considerations and the case study led us to suggest the following relationship among settling, demography and habitat selection: 1) Individuals search for suitable settling sites to inhabit and reproduce. 2) Their decision where and when to settle is a cost benefit decision. They weigh the benefit of searching for a high quality site against mortality due to increased searching time. 3) The individuals decision to settle determines the pre and post settling survivorship pattern. 4) Survivorship pattern dictates density pattern in time and space. 5) Density pattern in a given habitat determines its quality for the individual. 6) Settling selection among habitats and the number of safe sites controls the distribution of densities among habitats.

Predator - Prey Relationships: Rodent - Snail Interactions in the Central Negev Desert of Israel

We investigated the effects of increasing rodent (Acomys cahirinus and Gerbillus dasyurus) predation efficiency on their population density and the population of their prey, the desert snail (Trochoidae seetzenii). The study was carried out on a rocky hillslope in the Central Negev Desert, Israel. Rodent predation on snails is limited by the number of shelters for rodents in the area. In most natural conditions, more shelters are found on the upper than on the lower slope. We introduced artificial shelters along the slope. We then censused the number of rodents, snails, and of eaten snails for five years

17 - Livestock and Engineering Network in the Israeli Negev: Implications for Ecosystem Management

This chapter introduces the concept of engineering network. This concept encompasses the web of interactions among processes at the landscape, ecosystem, and community levels, emerging from the activity of an assemblage of ecosystem engineers (EEs). The development of the concept is based on the accumulative knowledge of functioning of natural, multiple EEs in the Negev. The chapter further develops the EE network concept by constructing an integrated model that combines natural and domestic organisms. The chapter concludes by discussing the utility of the model for ecosystem management issues related to pastoralism and recreation. The various management options in the Negev are based on the optimization of the spatial ratio between the two patch types created by the principal EEs. In fact, the crux of the management in the Negev is the optimal landscape modulation according to desired exploitation.

SETTLING BEHAVIOR OF THE DESERT ISOPOD HEMILEPISTUS REAUMURI IN RESPONSE TO VARIATION IN SOIL MOISTURE AND OTHER ENVIRONMENTAL CUES

ABSTRACT We report the results of three studies, one observational and two manipulative, that examine the settling behavior of isopods in response to soil moisture and other cues. In a census of isopod settling patterns in twenty-five 5 × 10 m plots arranged on a 200 m2 grid, isopods settled more densely in plots with more successful old burrows from the previous season, and in plots with more shrubs. Isopod settling was not correlated with soil moisture at 10 and 30 cm depths. In a manipulative experiment carried out over two years, isopods settled more densely in 3 × 3 m outdoor pens that received 20 mm of supplemental water in February than in unwatered plots. In a second experiment, 50 mm of water was added to open plots, and two densities of artificial holes were added as well. Isopods settled more densely in plots with added water, and settled much more densely in plots with artificial holes. Water did not significantly affect isopod survival or offspring weight. Unmanipulated plots with higher dens...