Ofer Ovadia | Ben Gurion University of the Negev (original) (raw)

Papers by Ofer Ovadia

Journal of Zoology, Jul 3, 2017

Animals in nature generally face fluctuating rather than constant environmental conditions. When ... more Animals in nature generally face fluctuating rather than constant environmental conditions. When given a choice, animals usually seek to minimize the variance of gain. However, it is clear that the avoidance of variance in energetic gain depends on several factors, including hunger level. While holding the mean prey encountered constant, we studied the effect of variance in prey arrival on the growth rates of two pit-building antlion species, Myrmeleon hyalinus and Cueta lineosa. Both species construct pit-traps in loose soils and ambush small prey in the same desert habitats, while differing in their preferred microhabitat: shaded vs. exposed to direct sunlight. We expected the light-preferring species to better tolerate variance in feeding than the shade-preferring species, owing to the former's higher stress tolerance and natural occurrence in microhabitats that are more likely poor with prey. While increasing variance in prey arrival reduced the growth rates of both species, this decrease was more pronounced in the species inhabiting the shaded and most likely prey-richer microhabitat. The greater variance tolerance of the light-preferring species stems from its ability to capture several prey items when almost simultaneously encountered. It could also be that this species has lower basal metabolic rate, which improves its starvation tolerance. These two antlion species differed in their prey capture success, starvation and thermal tolerance, and we thus suggest that their tolerance to variance in feeding opportunities and functional response offer an additional axis that enables them to coexist in the same desert habitats.

Population Ecology, Mar 29, 2008

Journal for Nature Conservation, Dec 1, 2022

Science of The Total Environment, Dec 1, 2015

• No additional burden of disease was found among graywater users in this study. • Rate of illnes... more • No additional burden of disease was found among graywater users in this study. • Rate of illnesses found was less than the Israeli national rate for gastroenteritis. • No specific exposures could be distinguished as a cause of illness.

Plant Ecology, Sep 7, 2011

Naturally growing plants are able to plastically respond to myriad environmental challenges and o... more Naturally growing plants are able to plastically respond to myriad environmental challenges and opportunities. When confronted with multiple stresses, plants are expected to be able to prioritize their responses according to immediacy and predicted acuteness of these stresses. Here, we studied the interactive effects of competition and nutrient deprivation on growth responses of damaged Trifolium purpureum plants to salivary cues of a mammalian grazer. Salivary cues elicited marked growth responses in damaged but otherwise wellnourished and competition-free T. purpureum plants; however, this positive effect was annulled under Stipa capensis competition and was reversed under nutrient deficiency. The results suggest that the magnitude and direction of the effects of salivary cues on plant growth depend on an intricate prioritization of plant responses to prevailing and expected challenges and that T. purpureum plants perceive competition as a more acute stress than grazing. While herbivore saliva enables plants to reliably differentiate between herbivory and physical damage, the limited correlation between prevailing and future herbivory might reduce the informative value of salivary cues, rendering their effects weaker than those of prevalent competition and nutrient deficiency, whose continued detrimental effects are usually highly predictive. The results stress the importance of further studying the interactive effects of the acuteness and reliability of prevailing and anticipated stresses, and the informational content and adaptive value of environmental cues under various environmental circumstances.

Conservation Biology, Oct 1, 2003

F1000Research, Aug 11, 2016

Journal of Plant Ecology, Nov 25, 2015

Aims Release of carbon from plant roots initiates a chain of reactions involving the soil microbi... more Aims Release of carbon from plant roots initiates a chain of reactions involving the soil microbial community and microbial predators, eventually leading to nutrient enrichment, a process known as the 'microbial loop'. However, root exudation has also been shown to stimulate nutrient immobilization, thereby reducing plant growth. Both mechanisms depend on carbon exudation, but generate two opposite soil nutrient dynamics. We suggest here that this difference might arise from temporal variation in soil carbon inputs. Methods We examined how continuous and pulsed carbon inputs affect the performance of wheat (Triticum aestivum), a fast-growing annual, while competing with sage (Salvia officinalis), a slow-growing perennial. We manipulated the temporal mode of soil carbon inputs under different soil organic matter (SOM) and nitrogen availabilities. carbon treatment included the following two carbon input modes: (i) continuous: a daily release of minute amounts of glucose, and (ii) Pulsed: once every 3 days, a short release of high amounts of glucose. the two carbon input modes differed only in the temporal dynamic of glucose, but not in total amount of glucose added. We predicted that pulsed carbon inputs should result in nutrient enrichment, creating favorable conditions for the wheat plants. Important Findings carbon addition caused a reduction in the sage total biomass, while increasing the total wheat biomass. In SOM-poor soil without nitrogen and in SOM-rich soil with nitrogen, wheat root allocation was higher under continuous than under pulsed carbon input. Such an allocation shift is a common response of plants to reduced nutrient availability. We thus suggest that the continuous carbon supply stimulated the proliferation of soil microorganisms, which in turn competed with the plants over available soil nutrients. the fact that bacterial abundance was at its peak under this carbon input mode support this assertion. Multivariate analyses indicated that besides the above described changes in plant biomasses and bacterial abundances, carbon supply led to an accumulation of organic matter, reduction in NO 3 levels and increased levels of NH 4 in the soil. the overall difference between the two carbon input modes resulted primarily from the lower total wheat biomass, and lower levels of NO 3 and soil PH characterizing pots submitted to carbon pulses, compared to those subjected to continuous carbon supply. carbon supply, in general, and carbon input mode, in particular, can lead to belowground chain reactions cascading up to affect plant performance.

Journal of Zoology, Sep 11, 2018

Spatio-temporal variation in aquatic habitat characteristics can have important implications for ... more Spatio-temporal variation in aquatic habitat characteristics can have important implications for the population and community dynamics of organisms utilizing these habitats. We studied the life-history responses of Culex pipiens larvae (Diptera: Culicidae) to multiple environmental factors associated with habitat drying by increasing larval density (directly affecting resource availability), temperature fluctuations (influencing physiological processes), and solute concentration due to evaporation (inducing an environmental stress), using a full-factorial design. We found that high density led to lower larval survival and to shorter development time. Larvae delayed their metamorphosis in response to fluctuating temperature. We detected inter-sexual differences in the effects of these two factors on adult body sizes, with high larval density leading to the emergence of smaller females, and fluctuating temperature translating to larger adult males. The two sexes also differed concerning the two-way interactive effects of different environmental factors on development time and on adult size. Our findings indicate that C. pipiens larvae respond to multiple environmental factors via phenotypic plasticity, rather than through bet-hedging. Future studies should account for additional inter-stage effects, rather than body size, such as adult fecundity, longevity, and dispersal.

Agriculture, Ecosystems & Environment, Apr 1, 2021

Abstract Habitat fragmentation entails major effects on many ecological processes. Theory offers ... more Abstract Habitat fragmentation entails major effects on many ecological processes. Theory offers two contradicting hypotheses for the expected effects of fragmentation on seed dispersal strategy. On the one hand, fragmentation may select for increased dispersal by purging poor dispersers that are incapable of moving between patches (spatial sorting). On the other hand, fragmentation may select for reduced dispersal due to the increased cost of leaving a colonized patch; especially whenever the surrounding matrix is hostile. Furthermore, fragmentation can have additional indirect effects on dispersal through its' effects on abiotic and biotic environmental characteristics, but these pathways are rarely accounted for. Empirical evidence testing these hypotheses in plants comes mainly from distinctly fragmented landscapes at either very large scales or very small scales, whereas studies at intermediate scales, such as those that characterize many agricultural landscapes are lacking. Here, we quantified direct and indirect effects of fragmentation-related characteristics, such as patch size and isolation level, on multiple dispersal-related traits of a heterocarpic annual plant in a fragmented agricultural landscape. Using a structural equation modelling approach, we examined whether fragmentation had positive or negative effects on seed dispersal potential and seed dispersal-related traits. Overall, we found more support for the spatial sorting hypothesis. However, the patterns were not simple, nor consistent across all traits and paths. The positive association between fragmentation and dispersal was mainly via a negative effect of connectivity on seed dispersal potential, but the effect of patch area on dispersal traits was less clear. We identified multiple direct and indirect effects of fragmentation-related patch characteristics on dispersal-related traits. Furthermore, the relative importance of direct and indirect effects was qualitatively different between overall effects. Our findings show that different characteristics of fragmented habitats may differentially affect different dispersal-related traits, and that these effects may take place via multiple paths, often leading to a complex relationship between fragmentation and dispersal.

Behavioral Ecology, Jul 1, 2003

We observed patch-use behavior by two gerbil species in a field setting and investigated how aggr... more We observed patch-use behavior by two gerbil species in a field setting and investigated how aggression and intrinsic decisionmaking interact to influence patch residence times. Results were interpreted by using a competing risk analysis model, which uniquely enabled us to estimate the intrinsic patch-leaving decisions independently of external interruptions of foraging bouts by aggression. The experiment was conducted in two 1-ha field enclosures completely surrounded by rodent-proof fences and included allopatric (only Gerbillus andersoni allenbyi) and sympatric (G. a. allenbyi and G. pyramidum) treatments. We predicted that increased food patch quality (i.e., habitat quality) should decrease intrinsic patch-leaving rates and increase rates of aggressive interactions involving the forager feeding in the patch (i.e., the occupant individual). We also anticipated that increasing population density should result in an increase in the rate of aggressive interactions involving the occupant individual. Our results supported the first two predictions, indicating a trade-off between foraging and aggression. However, the third prediction was realized only for G. a. allenbyi in allopatry. Furthermore, in allopatry, occupant G. a. allenbyi individuals with high competitive ranks were involved in aggressive interactions at lower rates than those with low competitive ranks. However, in sympatry, patchuse behavior of occupant G. a. allenbyi individuals was mainly influenced by aggressive behavior of G. pyramidum, which did not respond to their competitive rank. Thus, it should pay less for G. a. allenbyi to be aggressive in sympatric populations. The observed reduction in intraspecific aggression among individual G. a. allenbyi in the presence of G. pyramidum supports this assertion. We suggest that this reduction likely weakens the negative effect of intra-and interspecific density on the per capita growth rate of G. a. allenbyi. Because this would change the slope of the isocline of G. a. allenbyi, it could be an important mechanism promoting coexistence when habitat selection is constrained.

Mycorrhiza, Feb 23, 2021

The order of affiliations of the authors of the above article were rearranged and Ofer Ovadia one... more The order of affiliations of the authors of the above article were rearranged and Ofer Ovadia one of the co-authors was added as co-corresponding author in the authorship group and affiliation section. The original article has been corrected. Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Journal of Plant Ecology, Jun 26, 2021

We explored if and how seasonal fires interact with microhabitat type (i.e. under Pistacia shrub,... more We explored if and how seasonal fires interact with microhabitat type (i.e. under Pistacia shrub, under Cistus shrub or a canopy gap) to influence the composition of the germinable soil seed bank (GSSB) community in a typical eastern Mediterranean woodland. We conducted a field experiment, involving prescribed spring and autumn burns, and thereafter quantified the seed germination patterns using soil samples collected from both burned and adjacent unburned control plots. Soil temperature was significantly higher during autumn burns, while being more variable during spring burns. Fire caused overall reductions in GSSB density, richness and diversity. The reductions in GSSB richness and diversity were significantly stronger under Pistacia and Cistus shrubs located within plots subjected to autumn burns, and these patterns were mainly evident among annuals. GSSB density of dwarf shrubs was higher in samples collected from burned plots, and this pattern was more pronounced in samples collected under Pistacia and Cistus shrubs. Together with the appearance of unique species, seasonal fires led to significant changes in the composition of the GSSB community. Our results illustrate that seasonal fires interact with spatial heterogeneity to influence the composition of the GSSB community mostly via differential effects on the germination densities of annuals and dwarf shrubs. These findings imply that the increase in the frequency of seasonal fires, which has occurred in the eastern Mediterranean basin during the last few decades, may translate into a shift in eco-evolutionary selection pressures, operating on plants inhabiting this unique ecosystem.

Ecological Applications, Oct 23, 2017

Spatial synchrony plays an important role in dictating the dynamics of spatial and stagestructure... more Spatial synchrony plays an important role in dictating the dynamics of spatial and stagestructured populations. Here we argue that, unlike Moran effect where spatial synchrony is driven by exogenous factors, spatial correlation in intrinsic/local scale processes, can affect the level of spatial synchrony among distinct sub-populations, and therefore the persistence of the entire population. To explore this mechanism, we modelled the consequences of spatial heterogeneity in aquatic habitat quality, and that of temporal variation in local extinction probability, on the persistence of stagestructured mosquito populations. As a model system, we used two widely distributed mosquito species, Aedes albopictus and Culex pipiens, both key vectors of a range of infectious diseases.

Science of The Total Environment

Ornithological Applications, 2021

Understanding the causes of spread of overabundant species plays a key role in deciphering their ... more Understanding the causes of spread of overabundant species plays a key role in deciphering their invasion mechanisms, while providing managers with targeted management actions to control their spread. The objective of this research was to quantify the spread of Hooded Crow (Corvus cornix) in Israel and to elucidate the causes of its spread. Long-term occurrence data of Hooded Crow sightings were used to analyze the species range expansion rate. This dataset was analyzed with a range of climatic, normalized difference vegetation index (NDVI), and land-use variables. Analysis of opportunistic presence-only data, corrected for possible sampling biases, illustrated traveling waves of eastward expansion, from the Mediterranean coast into Israel’s central mountain range, and a star-like pattern of spread southward into the northwestern Negev desert. A diffusion equation model revealed an expansion rate of 1.60 km year–1. Land-use analysis revealed an affinity of sighted individuals toward...

Scientific Reports, 2021

Trap-building predators, such as web-building spiders and pit-building antlions, construct traps ... more Trap-building predators, such as web-building spiders and pit-building antlions, construct traps to capture their prey. These predators compete over sites that either enable the construction of suitable traps, are prey rich, or simply satisfy their abiotic requirements. We examined the effect of intraspecific competition over suitable space in pit-building wormlions. As expected, the ability of wormlions to select their favorable microhabitats—shaded or deep sand over lit or shallow sand—decreased with increasing density. Favorable microhabitats were populated more frequently by large than by small individuals and the density of individuals in the favorable microhabitat decreased with their increase in body mass. The advantage of large individuals in populating favorable microhabitats is nevertheless not absolute: both size categories constructed smaller pits when competing over a limited space compared to those constructed in isolation. The outcome of competition also depends on th...

Journal of Plant Ecology, 2021