Ido Tsurim

Winter bird communities in the northern Negev: species dispersal patterns, habitat use and implications for habitat conservation

Bird habitat conservation may require different management strategies for different seasonal bird assemblages. We studied habitat use by winter birds in forest and scrubland habitat patches in the northern Negev, Israel. Our goal was to assess whether differences in responses to landscape and habitat structure between breeding and non-breeding seasons require changes in future conservation plans that have been suggested for the Negev breeding bird community. We evaluated habitat and area effects on bird abundance and distribution and tested whether species habitat use during winter involves niche shifts. Compared with breeding birds, a larger proportion of winter bird species occupied both scrubland and forest. As in summer, forest bird species responded to habitat structure, whereas scrubland species were associated with both habitat structure and area. Resident birds disperse into habitats in which they were not present during summer. Consequently, for several species, the correlation between bird densities and environmental factors showed a better fit at the landscape rather than at the habitat scale. In addition, rather than niche shift, birds actually extended their niche breadth. Nest site selection may constrain bird distribution into a realized niche, smaller than their fundamental niche. Despite the scale differences in habitat use, the similar species diversity patterns between seasons suggest that both winter and summer birds would benefit from conservation of scrub patches larger than 50 ha, and enrichment of foliage layers within the planted forests.

Inter- and intra-specific density-dependent effects on life history and development strategies of larval mosquitoes.

We explored how inter- and intra-specific competition among larvae of two temporary-pool mosquito species, Culiseta longiareolata and Ochlerotatus caspius, affect larval developmental strategy and life history traits. Given that their larvae have similar feeding habits, we expected negative reciprocal inter-specific interactions. In a microcosm experiment, we found sex-specific responses of larval survival and development to both intra- and inter-specific larval competition. C. longiareolata was the superior competitor, reducing adult size and modifying larval developmental time of O. caspius. We observed two distinct waves of adult emergence in O. caspius, with clear sex-specific responses to its inter-specific competitor. In males, this pattern was not affected by C. longiareolata, but in females, the timing and average body size of the second wave strongly varied with C. longiareolata density. Specifically, in the absence of C. longiareolata, the second wave immediately followed the first wave. However, as C. longiareolata abundance increased, the second wave was progressively delayed and the resulting females tended to be larger. This study improves our understanding of the way intra- and inter-specific competition combine to influence the life histories of species making up temporary pond communities. It also provides strong evidence that not all individuals of a cohort employ the same strategies in response to competition.

Foraging Behavior of Urban Birds: Are Human Commensals Less Sensitive to Predation Risk than their Nonurban Counterparts

Abstract We hypothesized that the foraging behavior of urban birds would be less sensitive to variation in the cost of predation than that of nonurban bird species. We predicted that food-patch utilization by House Sparrows (Passer domesticus), a widespread human commensal, would be less sensitive to variation in predation risk than that of Spanish Sparrows (P. hispaniolensis), its nonurban counterpart. We applied the giving-up density (GUD) method to quantify patch use behavior of the two species with respect to distance from shelter. Our results indicated that Spanish Sparrows perceived a steep gradient of increased predation cost with increasing distance from shelter, while House Sparrows seemed indifferent to distance from shelter. These results support the hypothesis that the cost of predation has less effect on the foraging behavior of urban than nonurban birds, although alternative explanations include differences between species in the degree of neophobia, or variations in their ability to assess predation risk.

The Effect of Travel Costs on Food Hoarding in Gerbils

Abstract Hoarding strategies range between scatterhoarding (small multiple hoards) and larderhoarding (large single hoard). We hypothesized that spatial distribution of food affects hoarding strategy of 2 nocturnal psammophilic rodents, Gerbillus pyramidum and G. allenbyi. We used a modular arena to test the prediction that hoarding strategy would tend toward scatterhoarding as travel distance during foraging increases. We manipulated travel distance and studied its effect on hoarding behavior. G. allenbyi, as predicted, tended to scatterhoard as travel distance increased. G. pyramidum, however, reacted to changes in travel distance by moving the location of its larderhoard but did not scatterhoard. We suggest that hoarding strategy may be scale dependent and that gerbils will increase their number of hoards when energy costs of travel are sufficiently high.

Interactive effects of salinity and a predator on mosquito oviposition and larval performance

Oviposition habitat selection (OHS) is increasingly being recognized as playing a large role in explaining mosquito distributions and community assemblages. Most studies have assessed the role of single factors affecting OHS, while in nature, oviposition patterns are most likely explained by multiple, interacting biotic and abiotic factors. Determining how various factors interact to affect OHS is important for understanding metapopulation and metacommunity dynamics. We investigated the individual and interactive effects of three water salinities (0, 15 and 30 p.p.t. NaCl added) and the aquatic predator Anisops debilis Perplexa (Hemiptera: Notonectidae) on OHS and larval performance of the mosquitoes Ochlerotatus caspius Pallas and Culiseta longiareolata Macquart (Diptera: Culicidae) in outdoor-artificial-pool and laboratory experiments. C. longiareolata inhabited only freshwater pools, strongly avoided pools containing A. debilis, and larvae experienced lower survival in the presence of A. debilis. Salinity concentration interacted strongly with the predator in affecting OHS and larval survival of O. caspius; oviposition increased with increasing salinity in the absence of the predator and decreased with increasing salinity in the presence of the predator. O. caspius larval survival in predator-free pools was lowest in freshwater and highest at intermediate salinity. In predator pools, survival was highest at high salinity, where predation rate was shown to be lowest in the laboratory. Our results highlight that assessing the role of single factors in affecting mosquito distributions can be misleading. Instead, multiple factors may interact to affect oviposition patterns and larval performance.

Effects of fish cues on mosquito larvae development

We investigated the effects of predator-released kairomones on life history traits of larval Culex pipiens (Linnaeus). We compared the development time and survival of sibling larvae, reared in either water conditioned by the presence of Gambusia affinis (Baird and Girard) or fishless control-water. Our results indicate that larvae developing in fish-conditioned water (FCW) pupated faster than larvae in fishless-control water. The effect of FCW on larval survival was evident only in females. Surprisingly, FCW increased female survival. In both development-time and survival, boiling the water eliminated the FCW effect, supporting our hypothesis that fish conditioning is based on kairomones. Accelerated metamorphosis in response to predator released kairomones, evident in our results, is a rarely described phenomenon. Intuitively, when exposed to predator associated signals, aquatic larvae should metamorphose earlier to escape the higher risk of predation. However, theoretical models predict this outcome only under specific conditions. Indeed, longer - rather than shorter - time to metamorphosis is usually observed in response to predation risk. We argue that the response of larval mosquitoes to predation risk is context-dependent. Shortening larval development time may not be an exceptional response, but rather represents a part of a response spectrum that depends on the level of predation risk and resource abundance.

Species-Specific Non-Physical Interference Competition among Mosquito Larvae

Individuals of different sex, size or developmental stage can compete differently and hence contribute distinctively to population dynamics. In species with complex life cycles such as insects, competitive ability is often positively correlated with larval developmental stage. Yet, little is known on how the development and survival of early-instars is influenced by interference from late-instar larvae, especially at low densities when exploitative competition is expected to be negligible. Furthermore, the specificity and mechanisms by which interference competition operates are largely unknown. We performed two complementary experiments aiming to quantify the competitive effects of late instar Ochlerotatus caspius on early instar larvae at low densities and under high resource supply rate. The first experiment examined the net effect of interference by 4th on 1st instar O. caspius larvae, relative to the effect of 1st instars on themselves. The second experiment examined the effect of species-specific, non-physical interference competition (i.e., cage larvae) by 4th on 1st instar O. caspius larvae at low or high densities. Specifically, we compared the responses of O. caspius larvae raised in the presence of caged con- or hetero-specific, Culiseta longiareolata, with that of larvae in the empty-cage control group. As expected, interference from late instar larvae had a net negative effect on the development rate of first instars. In contrast, the presence of caged con-specifics (non-physical interference) accelerated the development rate of O. caspius, however, this pattern was only evident at the low density. Notably, no such pattern was detected in the presence of caged hetero-specifics. These results strongly suggest the existence of species-specific growth regulating semiochemicals.

Detrivory, competition, and apparent predation by Culiseta longiareolata in a temporary pool ecosystem

Larvae of the mosquito Culiseta longiareolata Macquart have been suggested as important species in desert and Mediterranean temporary pond ecosystems through their strong competitive abilities and as intra-guild predators. We examined their potential predatory effect on larvae of the abundant saltmarsh mosquito Ochlerotatus caspius. We did not find evidence for predatory effects of C. longiareolata on O. caspius larvae. We suggest that, at least in our system, C. longiareolata is an apparent predator. Namely, it does not actively prey on mobile victims, but rather feeds on the carcasses of its fallen competitors additional to its generally immobile food. Hence, we do not expect the occurrence of anti-predator behaviors in response to C. longiareolata presence, including larval development characteristics and oviposition habitat selection.

The structure of winter bird communities in the northern Negev shrub-steppes: Relating species composition to habitat structure

We describe the structural patterns of granivorous bird communities in a semiarid shrub-steppe during winter and examine whether and how habitat structure and productivity play roles in determining the structure of these bird communities. We used line transects and measurements of microhabitat use to describe the species diversity, species composition, and microhabitat use of the birds in semiarid shrub-steppe habitats across the northern Negev Desert, Israel. We then related those patterns to the structural characteristics of the habitats along the bird transects at two spatial scales. The bird communities in our study were not random samples of the species pool. Bird abundance and species diversity were correlated with the amount and distribution of perennial and annual vegetation; surrogates of seed abundance and habitat structure, respectively. Species assemblies across the landscape were organized in a nested-subsets structure possibly related to habitat structure. Indeed, species composition was rel...

The Effect of Food and Shelter on Habitat Selection by Granivorous Birds Over-Wintering in Shrub Steppes of the Northern Negev, Israel

Habitat structure and productivity are suggested as important determinants of community structure. We manipulated food abundance and shelter availability in an ephemeral community of wintering passerine birds by augmenting seeds and by adding a large bush to experimental plots in the northern Negev, Israel. In Experiment-1, we augmented seven 1-ha subplots with seeds for 5 weeks, keeping adjacent subplots as controls. We then switched treatments between the subplots for 4 additional weeks. In Experiment-2, we had five independent 4-ha plots, divided into four 1-ha subplots allocated to four treatments: Control, Seed Augmentation, Shelter Addition, and both Seed Augmentation and Shelter Addition. Species richness and bird abundance increased with food abundance, suggesting that birds either move into sites with more food, allocate more time to foraging in them, or both. bird abundance and species richness were not affected by the shelter addition. Food abundance affected species diversity only during Exper...