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Benedikt Grothe - One of the best experts on this subject based on the ideXlab platform.

  • Optogenetic Control of Neural Circuits in the Mongolian Gerbil.
    Frontiers in Cellular Neuroscience, 2018
    Co-Authors: Stefan Keplinger, Barbara Beiderbeck, Stylianos Michalakis, Martin Biel, Benedikt Grothe, Lars Kunz
    Abstract:

    The Mongolian Gerbil (Meriones unguiculatus) is widely used as a model organism for the human auditory system. Its hearing range covers most of ours and it uses the same mechanisms for sound localization. The auditory circuits underlying these functions have been characterized. However, important mechanistic details are still under debate. To elucidate missing mechanistic details precise and reversible optogenetic manipulation of neuronal activity in these circuitries is required. However, gene transfer or even genomic modification is scarcely established in the Mongolian gerbil. Here, we have established a reliable, gene delivery system using AAV8(Y337F)-pseudotyped recombinant adeno-associated virus (AAV) 2 based vector in combination with the pan-neural human synapsin (hSyn) promoter driving neuron-specific expression of CatCH (Ca2+-permeable channelrhodopsin) or NpHR3.0 (Natronomonas pharaonis halorhodopsin). After stereotactical injection into the gerbil’s auditory brainstem (medial nucleus of the trapezoid body, dorsal nucleus of the lateral lemniscus) and midbrain (inferior colliculus), we characterized CatCH and/or NpHR3.0 transduced neurons in acute brain slices by means of whole-cell patch-clamp recordings. As electrical properties of optogenetic tools strongly depend on neuronal biophysics, this parameterization is crucial for their in vivo application. In a proof of principle experiment in anaesthetized Gerbils we could strongly suppress sound evoked neural responses in the dorsal nucleus of the lateral lemniscus (DNLL) and inferior colliculus (IC) by light activation of NpHR3.0. In summary, by establishing gene delivery and optogenetic tools in the Mongolian gerbil we have paved the way for future studies of the auditory circuitries in this model system.

  • Image_1_Optogenetic Control of Neural Circuits in the Mongolian Gerbil.PDF
    2018
    Co-Authors: Stefan Keplinger, Barbara Beiderbeck, Stylianos Michalakis, Martin Biel, Benedikt Grothe, Lars Kunz
    Abstract:

    The Mongolian gerbil (Meriones unguiculatus) is widely used as a model organism for the human auditory system. Its hearing range is very similar to ours and it uses the same mechanisms for sound localization. The auditory circuits underlying these functions have been characterized. However, important mechanistic details are still under debate. To elucidate these issues, precise and reversible optogenetic manipulation of neuronal activity in this complex circuitry is required. However, genetic and genomic resources for the Mongolian gerbil are poorly developed. Here, we demonstrate a reliable gene delivery system using an AAV8(Y337F)-pseudotyped recombinant adeno-associated virus (AAV) 2-based vector in which the pan-neural human synapsin (hSyn) promoter drives neuron-specific expression of CatCH (Ca2+-permeable channelrhodopsin) or NpHR3.0 (Natronomonas pharaonis halorhodopsin). After stereotactic injection into the gerbil’s auditory brainstem (medial nucleus of the trapezoid body, dorsal nucleus of the lateral lemniscus) and midbrain [inferior colliculus (IC)], we characterized CatCH- and/or NpHR3.0-transduced neurons in acute brain slices by means of whole-cell patch-clamp recordings. As the response properties of optogenetic tools strongly depend on neuronal biophysics, this parameterization is crucial for their in vivo application. In a proof-of-principle experiment in anesthetized Gerbils, we observed strong suppression of sound-evoked neural responses in the dorsal nucleus of the lateral lemniscus (DNLL) and IC upon light activation of NpHR3.0. The successful validation of gene delivery and optogenetic tools in the Mongolian gerbil paves the way for future studies of the auditory circuits in this model system.

  • Sound Localization in Noise by Gerbils and Humans
    Journal of the Association for Research in Otolaryngology, 2012
    Co-Authors: Andrea Lingner, Lutz Wiegrebe, Benedikt Grothe
    Abstract:

    Detection and localization of a target sound in the presence of concurrent, spatially distributed masking sounds is one of the most challenging tasks for the mammalian auditory system. Previous studies demonstrated that the ability to localize signals is decreased by interfering noise. In order to directly compare the behavioral performance in a signal processing task in noise between Gerbils and humans in the free sound field, we quantified their localization ability for a low-frequency signal in the presence of six masking noise sources surrounding the subject. Thresholds were measured both for masking noises that were correlated or uncorrelated across the masking sources. Overall, the Gerbils required a higher signal/noise ratio to detect the low-frequency signal than the humans; that is, the behavioral performance of the Gerbils was considerably worse than that of the humans. Moreover, switching from maskers that were uncorrelated across the masking sources to correlated maskers resulted in more masking in Gerbils but in a release from masking in humans. These results would suggest that the gerbil may not be a good animal model for binaural processing. However, simulations of the localization thresholds in a numerical model of binaural processing in Gerbils and humans reveal that both the inferior overall performance in Gerbils and the opposite effect of masker correlation on the detection thresholds can be attributed to the smaller head size and the wider peripheral auditory filters in Gerbils. Thus, the current data indicate that the binaural processor itself (i.e., the evaluation of signals coming from the two ears) is equally sensitive in Gerbils and humans. However, the physical limitations imposed by the small head prevent the gerbil from performing equally well in the current paradigm.

David S Lindsay - One of the best experts on this subject based on the ideXlab platform.

  • effects of artemisinin and artemisia extracts on haemonchus contortus in Gerbils meriones unguiculatus
    Veterinary Parasitology, 2011
    Co-Authors: Jill Squires, David S Lindsay, Jorge F S Ferreira, Anne M Zajac
    Abstract:

    Abstract Haemonchus contortus is a blood-sucking abomasal parasite of small ruminants that is responsible for major losses to producers worldwide. Resistance of this nematode to commercial anthelmintics has produced a demand for alternative control methods. Plants in the genus Artemisia have traditionally been used as anthelmintics and whole plants and plant extracts have demonstrated activity against gastrointestinal nematodes in several studies. In addition, Artemisia annua is the sole commercial source of artemisinin, the raw material used to produce drugs effective against the hemoprotozoan malaria parasites (Plasmodium species). Artemisinin derivatives have also shown efficacy against some trematodes, including Fasciola hepatica and Schistosoma species. In this study, artemisinin was tested for efficacy against H. contortus in a gerbil model of infection. Also tested in the gerbil model were an aqueous extract, an ethanolic extract and the essential oil of A. annua, and an ethanolic extract of Artemisia absinthium. In all experiments, Gerbils were infected with 600 third-stage H. contortus larvae. In experiment 1, Gerbils were treated orally with 400 milligrams per kilogram body weight (mg/kg BW) artemisinin once or 200 mg/kg BW artemisinin daily for 5 days (Days 4–8 post-infection). In experiment 2, Gerbils were treated daily for 5 days with 600 mg/kg BW of A. annua ethanolic or aqueous extract. In Experiment 3, Gerbils were treated with 1000 mg/kg BW of A. annua or A. absinthium ethanolic extract or with 300 mg/kg BW of A. annua essential oil daily for five consecutive days (Days 4–8 post-infection). No significant effects of treatment were seen with artemisinin or any of the Artemisia species extracts at the dosages studied. The non-ionic surfactant Labrosol® was an effective nontoxic solvent for delivery of hydrophilic plant extracts and the lipophilic essential oil used in the study.

  • Gerbil model of acute neosporosis.
    Veterinary Parasitology, 2005
    Co-Authors: Sheela Ramamoorthy, Nammalwar Sriranganathan, David S Lindsay
    Abstract:

    Experimental infections with the NC-1 strain of Neospora caninum were conducted in Gerbils (Meriones unguiculatus) to determine their acute responses to experimental intraperitoneal infection. Five groups of five female Gerbils were used and they were intraperitoneally infected with 1x10(6), 2x10(6), 3x10(6), 4x10(6) or 5x10(6) tachyzoites. Gerbils in all groups developed clinical signs of neosporosis which consisted of inactivity 4-5 days post-inoculation. Morbidity and mortality were observed in all groups. Grossly there was a clear fibrinous exudate in the abdominal cavity and adhesions of the spleen and pancreas to the stomach in Gerbils suffering from acute neosporosis. The LD50 was calculated as 9.3x10(5) tachyzoites per gerbil. The results indicate that Gerbils can be used as a suitable model of acute neosporosis. This model can be used to screen candidate treatments and to test the efficacy of vaccines for neosporosis without the need to use histology or PCR to demonstrate treatment efficacy.

  • Gerbils meriones unguiculatus are highly susceptible to oral infection with neospora caninum oocysts
    Parasitology Research, 2000
    Co-Authors: J P Dubey, David S Lindsay
    Abstract:

    Laboratory-reared Gerbils (Meriones unguiculatus) were found to be highly susceptible to oral infection with Neospora caninum (NC-Liv strain) oocysts. Gerbils fed ∼1000 oocysts became sick or died at 6–13 days post feeding of oocysts (PFO). N. caninum was isolated in cell culture and from γ-interferon-knockout mice inoculated with homogenates of mesenteric lymph nodes of Gerbils examined as early as 1 day PFO. Numerous N. caninum tachyzoites were found in ulcerative lesions in the intestines of Gerbils examined at 7–9 days PFO. In a gerbil fed 10 oocysts, N. caninum tachyzoites were found in lesions in the brain. Gerbils fed 10 oocysts developed antibodies to N. caninum by 18 days PFO as determined by the Neospora agglutination test (titers ≥1:500). All Gerbils remained negative for antibodies to Toxoplasma gondii as determined by the Toxoplasma agglutination test.

Burt P. Kotler - One of the best experts on this subject based on the ideXlab platform.

  • Novel predator recognition by Allenby's gerbil (Gerbillus andersoni allenbyi ): do Gerbils learn to respond to a snake that can “see” in the dark?
    Israel Journal of Ecology and Evolution, 2016
    Co-Authors: Sonny S. Bleicher, Joel S. Brown, Keren Embar, Burt P. Kotler
    Abstract:

    Unlike desert rodents from North America, Allenby's gerbil (Gerbillus andersoni allenbyi) from the Negev Desert, Israel has evolved with snakes that do not have heat-sensitive sensory pits that enhance night vision. Does this history affect their ability to assess and respond to a snake that has this ability? As a test, we exposed Gerbils to risk of predation from various predators, including snakes, owls, and foxes. The snakes included the Saharan horned viper (Cerastes cerastes) and the sidewinder rattlesnake (Crotalus cerastes). The former snake lacks sensory pits and shares a common evolutionary history with the gerbil. The latter snake, while convergent evolutionarily on the horned viper, has sensory pits and no prior history with the gerbil. The Gerbils exploited depletable resource patches similarly, regardless of snake species and moon phase. While the Gerbils did not respond to the novel snake as a greater threat than their familiar horned viper, the Gerbils were cognizant that the novel predator...

  • The foraging response of Gerbils to a gradient of owl numbers
    Evolutionary Ecology Research, 2011
    Co-Authors: Justin R. St. Juliana, Joel S. Brown, Burt P. Kotler, Shomen Mukherjee, Amos Bouskila
    Abstract:

    Background: While many studies have addressed a prey’s behavioural responses to predators, very few have tested how the prey’s anti-predator behaviour changes as a function of predator number. Hypotheses: Encounter rate with predators should increase with increasing numbers of predators, thus increasing the predation risk (a cost of foraging) for prey individuals. With increased predation risk, prey animals should quit foraging sooner, and leave more resources behind. Increased predation risk should also cause prey to devote more attention to predator detection and less to foraging. This redirection of attention should result in lower harvest rates, and a higher quitting harvest rate for the prey. Organisms: Prey: Allenbyi’s gerbil, Gerbillus andersoni allenbyi , a psammophilic, 25-g desert rodent. Predator: barn owl, Tyto alba . Methods: We allowed Gerbils to forage in a large outdoor aviary in Sede Boker, Israel, subject to various risks of predation (i.e. in the presence of 0, 1, 2, or 3 barn owls). We measured gerbil giving-up densities (GUDs), the amount of food left behind by Gerbils foraging in artificial resource patches. In each trial, resource patches were set up in different microhabitats with different arrangements of seeds. Comparing GUDs between these resource patches provided a gauge of the Gerbils’ perceived risk of predation and apprehension (a forager’s redirection of attention from foraging to predator detection). Results: Gerbils had higher GUDs when owls were present. Furthermore, Gerbils increased their apprehensiveness when more owls were present in the aviary. The increase in gerbil GUD with each additional owl was less than additive.

  • Foraging games between Gerbils and their predators: temporal dynamics of resource depletion and apprehension in Gerbils
    Evolutionary Ecology Research, 2002
    Co-Authors: Burt P. Kotler, Joel S. Brown, Shaan Gresser, David T. Ganey, Amos Bouskila
    Abstract:

    Predator–prey interactions constitute a foraging game when prey individuals manage risk from predators and predator individuals manage fear in their prey. As tools for managing risk, clever prey can use time allocation and apprehension (redirecting attention from foraging to predator detection). One such foraging game occurs between Gerbils and their predators on the sand dunes of the Negev Desert. Here, interacting species of Gerbils compete for patches of seeds that renew daily by afternoon winds. In such circumstances, Gerbils are expected to deplete resource patches over the course of the night, the predators are expected to hunt when gerbil activity is highest, and Gerbils are expected to be most apprehensive when predators are most active and most deadly. We tested these predictions for Gerbils in two field experiments using seed trays to measure resource depletion, gerbil activity and apprehension over the course of the night, between the bush and open microhabitats and at four moon phases (new, half waxing, full and half waning). Gerbils depleted seed resources more quickly in the bush microhabitat than the open and more quickly at new moon than at other moon phases. Gerbil activity at new moon was high throughout most of the night, but decreased towards dawn. In contrast, activity at full moon was generally low, but increased towards dawn. The two gerbil species Gerbillus andersoni allenbyi and G. pyramidum partitioned the night, with G. pyramidum visiting resource patches earlier in the night and encountering a richer, but more risky environment, and G. a. allenbyi foraging later in an environment characterized by fewer seed resources, but lower risk. The same pattern extended over moon phases, with G. pyramidum foraging relatively more at full and waning half moon. Apprehension by Gerbils was higher early in the night than later and higher at full moon than new moon. Schedules of apprehension changed according to moon phase and may have differed between the two Gerbils. Finally, apprehension was higher in the open microhabitat, although the opposite was true at the beginning of the night. This foraging game affects three trophic levels, including the effect of the Gerbils on the availability and

  • Attention, 'apprehension' and Gerbils searching in patches
    2001
    Co-Authors: Sasha R. X. Dall, Burt P. Kotler, Amos Bouskila
    Abstract:

    In this paper, we consider the attentional demands associated with detecting and responding to predators, or ‘apprehension’, and the within-patch search of Allenby’s Gerbils, Gerbillus andersoni allenbyi. We, thus, present a first empirical investigation of the indirect, informational consequences of perceived predation risk. Specifically, we focus on the ability to track the quality of seed patches in sandy habitats. There are two potential effects here; since instantaneous intake rate (or some proxy) is the key parameter of interest to an optimal forager, apprehension can interfere with the estimation of: (1) the number of food items captured, and/or (2) the time taken to capture them (the ability to locate food items). Only (2) will have a consistent effect on patch quality, and we test the hypothesis that increased predation risk reduces gerbil search efficiency. We therefore quantified gerbil search paths in patches of uniform seed distribution that differed in their associated risks of predation by manipulating the presence of barn owls, Tyto alba, and light in an aviary. Gerbil search was more random under risky conditions. We discuss the implications of this result for information processing and patch use under predation risk, and the foraging games between Gerbils and owls in the Negev Desert.

  • foraging and community consequences of seed size for coexisting negev desert granivores
    Oikos, 2000
    Co-Authors: Jessica E Garb, Burt P. Kotler, Joel S. Brown
    Abstract:

    We examined the effects of seed size on patch use and diet selection for three co-existing Negev Desert granivores: Allenby’s gerbil (Gerbillus allenbyi ), greater Egyptian sand gerbil (Gerbillus pyramidum), and crested lark (Galerida cristata). We manipulated size and spatial distribution of seeds in experimental food patches and quantified foraging behavior by measuring giving-up densities (GUDs: the amount of food remaining in a resource patch following exploitation by a forager). In one experiment, we presented small (B1.4 mm in diameter cracked wheat), medium (2.0‐3.3 mm), and large (\3.4 mm) seeds in separate trays; in a second, we presented small and medium seeds separately and mixed together. Gerbils had a higher handling time efficiency on smaller seeds, but a much higher encounter probability on larger seeds (20 times higher on large than medium seeds, and 2‐5 times higher on medium than small seeds). This led Gerbils to have significantly lower GUDs on larger seeds than smaller seeds and to harvest a higher proportion of the larger seeds. When presented with rich and poor patches, G. allenbyi tended to equalize GUDs in both patches, indicating a quitting harvest rate rule for patch exploitation. In contrast, larks appeared to use a fixed time rule for patch exploitation. For larks, seed size did not influence encounter probabilities, and they showed no seed-size selectivity. Still, larks had higher handling efficiencies on smaller than larger seeds, and consequently had a significantly lower GUD on small than medium seeds. Despite large differences between the Gerbils and larks in their foraging, our results do not support species coexistence via seed-size partitioning: the larks had much higher GUDs than the Gerbils on all seed sizes. Nonetheless, seed size, seed abundance, seed distribution and the animal’s patch use behavior all played major roles in determining Gerbils’ and larks’ diet selectivities and GUDs.

J P Dubey - One of the best experts on this subject based on the ideXlab platform.

  • first isolation of neospora caninum from the feces of a naturally infected dog
    Journal of Parasitology, 2001
    Co-Authors: Walter Basso, L Venturini, M C Venturini, S K Shen, D E Hill, O C H Kwok, J P Dubey
    Abstract:

    Neospora caninum is a major cause of abortion in cattle worldwide. Cattle become infected with N. caninum by ingesting oocysts from the environment or transplacentally from dam to fetus. Experimentally, dogs can act as definitive hosts, but dogs excrete few oocysts after ingesting tissue cysts. A natural definitive host was unknown until now. In the present study, N. caninum was isolated from the feces of a dog. Gerbils (Meriones unguiculatus) fed feces from the dog developed antibodies to N. caninum in the Neospora caninum agglutination test, and tissue cysts were found in their brains. Neospora caninum was isolated in cell culture and in gamma-interferon gene knockout mice inoculated with brain homogenates of infected Gerbils. The DNA obtained from fecal oocysts of the dog, from the brains of Gerbils fed dog feces, and from organisms isolated in cell cultures inoculated with gerbil brains was confirmed as N. caninum. The identification of N. caninum oocyst by bioassay and polymerase chain reaction demonstrates that the dog is a natural definitive host for N. caninum.

  • Gerbils meriones unguiculatus are highly susceptible to oral infection with neospora caninum oocysts
    Parasitology Research, 2000
    Co-Authors: J P Dubey, David S Lindsay
    Abstract:

    Laboratory-reared Gerbils (Meriones unguiculatus) were found to be highly susceptible to oral infection with Neospora caninum (NC-Liv strain) oocysts. Gerbils fed ∼1000 oocysts became sick or died at 6–13 days post feeding of oocysts (PFO). N. caninum was isolated in cell culture and from γ-interferon-knockout mice inoculated with homogenates of mesenteric lymph nodes of Gerbils examined as early as 1 day PFO. Numerous N. caninum tachyzoites were found in ulcerative lesions in the intestines of Gerbils examined at 7–9 days PFO. In a gerbil fed 10 oocysts, N. caninum tachyzoites were found in lesions in the brain. Gerbils fed 10 oocysts developed antibodies to N. caninum by 18 days PFO as determined by the Neospora agglutination test (titers ≥1:500). All Gerbils remained negative for antibodies to Toxoplasma gondii as determined by the Toxoplasma agglutination test.

Joel S. Brown - One of the best experts on this subject based on the ideXlab platform.

  • Novel predator recognition by Allenby's gerbil (Gerbillus andersoni allenbyi ): do Gerbils learn to respond to a snake that can “see” in the dark?
    Israel Journal of Ecology and Evolution, 2016
    Co-Authors: Sonny S. Bleicher, Joel S. Brown, Keren Embar, Burt P. Kotler
    Abstract:

    Unlike desert rodents from North America, Allenby's gerbil (Gerbillus andersoni allenbyi) from the Negev Desert, Israel has evolved with snakes that do not have heat-sensitive sensory pits that enhance night vision. Does this history affect their ability to assess and respond to a snake that has this ability? As a test, we exposed Gerbils to risk of predation from various predators, including snakes, owls, and foxes. The snakes included the Saharan horned viper (Cerastes cerastes) and the sidewinder rattlesnake (Crotalus cerastes). The former snake lacks sensory pits and shares a common evolutionary history with the gerbil. The latter snake, while convergent evolutionarily on the horned viper, has sensory pits and no prior history with the gerbil. The Gerbils exploited depletable resource patches similarly, regardless of snake species and moon phase. While the Gerbils did not respond to the novel snake as a greater threat than their familiar horned viper, the Gerbils were cognizant that the novel predator...

  • The foraging response of Gerbils to a gradient of owl numbers
    Evolutionary Ecology Research, 2011
    Co-Authors: Justin R. St. Juliana, Joel S. Brown, Burt P. Kotler, Shomen Mukherjee, Amos Bouskila
    Abstract:

    Background: While many studies have addressed a prey’s behavioural responses to predators, very few have tested how the prey’s anti-predator behaviour changes as a function of predator number. Hypotheses: Encounter rate with predators should increase with increasing numbers of predators, thus increasing the predation risk (a cost of foraging) for prey individuals. With increased predation risk, prey animals should quit foraging sooner, and leave more resources behind. Increased predation risk should also cause prey to devote more attention to predator detection and less to foraging. This redirection of attention should result in lower harvest rates, and a higher quitting harvest rate for the prey. Organisms: Prey: Allenbyi’s gerbil, Gerbillus andersoni allenbyi , a psammophilic, 25-g desert rodent. Predator: barn owl, Tyto alba . Methods: We allowed Gerbils to forage in a large outdoor aviary in Sede Boker, Israel, subject to various risks of predation (i.e. in the presence of 0, 1, 2, or 3 barn owls). We measured gerbil giving-up densities (GUDs), the amount of food left behind by Gerbils foraging in artificial resource patches. In each trial, resource patches were set up in different microhabitats with different arrangements of seeds. Comparing GUDs between these resource patches provided a gauge of the Gerbils’ perceived risk of predation and apprehension (a forager’s redirection of attention from foraging to predator detection). Results: Gerbils had higher GUDs when owls were present. Furthermore, Gerbils increased their apprehensiveness when more owls were present in the aviary. The increase in gerbil GUD with each additional owl was less than additive.

  • Foraging games between Gerbils and their predators: temporal dynamics of resource depletion and apprehension in Gerbils
    Evolutionary Ecology Research, 2002
    Co-Authors: Burt P. Kotler, Joel S. Brown, Shaan Gresser, David T. Ganey, Amos Bouskila
    Abstract:

    Predator–prey interactions constitute a foraging game when prey individuals manage risk from predators and predator individuals manage fear in their prey. As tools for managing risk, clever prey can use time allocation and apprehension (redirecting attention from foraging to predator detection). One such foraging game occurs between Gerbils and their predators on the sand dunes of the Negev Desert. Here, interacting species of Gerbils compete for patches of seeds that renew daily by afternoon winds. In such circumstances, Gerbils are expected to deplete resource patches over the course of the night, the predators are expected to hunt when gerbil activity is highest, and Gerbils are expected to be most apprehensive when predators are most active and most deadly. We tested these predictions for Gerbils in two field experiments using seed trays to measure resource depletion, gerbil activity and apprehension over the course of the night, between the bush and open microhabitats and at four moon phases (new, half waxing, full and half waning). Gerbils depleted seed resources more quickly in the bush microhabitat than the open and more quickly at new moon than at other moon phases. Gerbil activity at new moon was high throughout most of the night, but decreased towards dawn. In contrast, activity at full moon was generally low, but increased towards dawn. The two gerbil species Gerbillus andersoni allenbyi and G. pyramidum partitioned the night, with G. pyramidum visiting resource patches earlier in the night and encountering a richer, but more risky environment, and G. a. allenbyi foraging later in an environment characterized by fewer seed resources, but lower risk. The same pattern extended over moon phases, with G. pyramidum foraging relatively more at full and waning half moon. Apprehension by Gerbils was higher early in the night than later and higher at full moon than new moon. Schedules of apprehension changed according to moon phase and may have differed between the two Gerbils. Finally, apprehension was higher in the open microhabitat, although the opposite was true at the beginning of the night. This foraging game affects three trophic levels, including the effect of the Gerbils on the availability and

  • foraging and community consequences of seed size for coexisting negev desert granivores
    Oikos, 2000
    Co-Authors: Jessica E Garb, Burt P. Kotler, Joel S. Brown
    Abstract:

    We examined the effects of seed size on patch use and diet selection for three co-existing Negev Desert granivores: Allenby’s gerbil (Gerbillus allenbyi ), greater Egyptian sand gerbil (Gerbillus pyramidum), and crested lark (Galerida cristata). We manipulated size and spatial distribution of seeds in experimental food patches and quantified foraging behavior by measuring giving-up densities (GUDs: the amount of food remaining in a resource patch following exploitation by a forager). In one experiment, we presented small (B1.4 mm in diameter cracked wheat), medium (2.0‐3.3 mm), and large (\3.4 mm) seeds in separate trays; in a second, we presented small and medium seeds separately and mixed together. Gerbils had a higher handling time efficiency on smaller seeds, but a much higher encounter probability on larger seeds (20 times higher on large than medium seeds, and 2‐5 times higher on medium than small seeds). This led Gerbils to have significantly lower GUDs on larger seeds than smaller seeds and to harvest a higher proportion of the larger seeds. When presented with rich and poor patches, G. allenbyi tended to equalize GUDs in both patches, indicating a quitting harvest rate rule for patch exploitation. In contrast, larks appeared to use a fixed time rule for patch exploitation. For larks, seed size did not influence encounter probabilities, and they showed no seed-size selectivity. Still, larks had higher handling efficiencies on smaller than larger seeds, and consequently had a significantly lower GUD on small than medium seeds. Despite large differences between the Gerbils and larks in their foraging, our results do not support species coexistence via seed-size partitioning: the larks had much higher GUDs than the Gerbils on all seed sizes. Nonetheless, seed size, seed abundance, seed distribution and the animal’s patch use behavior all played major roles in determining Gerbils’ and larks’ diet selectivities and GUDs.

  • mechanisms of coexistence of optimal foragers as determinants of local abundances and distributions of desert granivores
    Journal of Mammalogy, 1999
    Co-Authors: Burt P. Kotler, Joel S. Brown
    Abstract:

    Foraging theory can be applied to the study of ecological communities. We developed and tested several local mechanisms of species coexistence based on foraging theory for a desert granivore community in a heterogeneous landscape in the Negev Desert, Israel. The most common species were Allenby's gerbil ( Gerbillus allenbyi ), Wagner's gerbil ( Gerbillus dasyurus ), and crested lark ( Galerida cristata ). Allenby's Gerbils were most abundant on sandy substrates; Wagner's Gerbils were most abundant on cobble and loess substrates; crested larks occurred across all three. To test among predictions of the different mechanisms of coexistence, we used live-trapping and counts to census rodents and birds, recorded spoor in sand-tracking plots to determine habitat-specific activity patterns, and measured giving-up densities in depletable food patches to estimate relative foraging efficiencies on different substrates and within different habitats. Allenby's gerbil had an advantage in habitat selection by being the most efficient forager (lowest giving-up densities on seeds in feeding trays) in the sandy habitat. The crested lark was the tolerant forager. Its foraging abilities were affected little by escape substrate, foraging substrate, or food type. As a result, the crested lark had three advantages: it was the most efficient forager in the loess habitat, it was a better insectivore than the Gerbils, and its diurnal habit allowed it first access to seed patches that renew in the afternoon in the sandy habitat when winds typically arise. In response to our measures of foraging aptitude, Wagner's gerbil revealed no advantage over the other species, and factors promoting its success eluded our proposed mechanisms of species coexistence. Foraging ecology and community ecology can be integrated to understand local species distributions, abundances, and community structure and organization. Uniform conceptual and methodological techniques can be applied across taxa and communities. We were able to relatively quickly test which mechanisms of coexistence apply. In the community we studied, there were two species whose presence we feel we understood and one species whose presence remained an enigma.