Interspecific Competitive Relationships Research Articles

Food-plant choice of seven dominant grasshopper species in the Xinjiang grasslands

Feeding habits and competitive interactions among dominant grasshopper species in the Xinjiang grasslands (China) were studied under natural conditions through microscopic analyses of insect crop contents. Sex-specific and interindividual differences in feeding habits and interspecific competition were investigated. Analyses of ecological niche width and overlap revealed potential competition among grasshoppers. The results showed significant difference in the sex-specific variations in the feeding habits of the seven grasshoppers; sex-specific variations in feeding range and preferred plants were observed, with females feeding more extensively on host plants, and female and male adults choosing to feed on different plant species. Individuals of all seven grasshoppers showed different degrees of dietary variance, with oligophagous grasshoppers (Oedaleus decorus males, Dericorys annulata, and Bryodema gebleri males) showing a smaller degree of individual dietary variance than polyphagous grasshoppers (Oedipoda caerulescens, Calliptamus coelesyriensis females, Calliptamus barbarus, and Notostaurus albicornis); Calliptamus coelesyriensis and Notostaurus albicornis showed the greatest individual variance in their diets. Oedaleus decorus, Bryodema gebleri, and Calliptamus barbarus consumed primarily Poaceae and exhibited varying foot-plant choice. For example, Oedaleus decorus was observed to have high- preference feeding for Poa annua, Bryodema gebleri for Stipa capillata, and Calliptamus barbarus for Setaria viridis. Dericorys annulata fed primarily on Amaranthaceae, Notostaurus albicornis fed primarily on Poaceae and Amaranthaceae, and Oedipoda caerulescens fed primarily on Asteraceae. Calliptamus barbarus exhibited strong interspecific competition with Oedaleus decorus and Calliptamus coelesyriensis, and Bryodema gebleri demonstrated the strongest interspecific competition with all six other species. Considering the influence of sex on interspecific competition among grasshoppers enhances our understanding of interspecific competitive relationships.

Effect of interspecific competitive relationships involving Tubastraea spp. (Scleractinia, Dendrophyllidae) and Palythoa caribaeorum (Zoantharia, Sphenopidae)

Effect of interspecific competitive relationships involving Tubastraea spp. (Scleractinia, Dendrophyllidae) and Palythoa caribaeorum (Zoantharia, Sphenopidae)

Microbial community structure and denitrification responses to cascade low-head dams and their contribution to eutrophication in urban rivers

Low-head dams are one of the most common hydraulic facilities, yet they often fragment rivers, leading to profound changes in aquatic biodiversity and river eutrophication levels. Systematic assessments of river ecosystem structure and functions, and their contribution to eutrophication, are however lacking, especially for urban rivers where low-head dams prevail. In this study, we address this gap with a field survey on microbial community structure and ecosystem function, in combination with hydrological, environmental and ecological factors. Our findings revealed that microbial communities showed significant differences among the cascade impoundments, which may be due to the environment heterogeneity resulting from the cascade low-head dams. The alternating lentic–lotic flow environment created by the low-head dams caused nutrient accumulation in the cascade impoundments, enhancing environmental sorting and interspecific competition relationships, and thus possibly contributing to the reduction in sediment denitrification function. Decreased denitrification led to excessive accumulation of nutrients, which may have aggravated river eutrophication. In addition, structural equation model analysis showed that flow velocity may be the key controlling factor for river eutrophication. Therefore, in the construction of river flood control and water storage systems, the location, type and water storage capacity of low-head dams should be fully considered to optimize the hydrodynamic conditions of rivers. To summarize, our findings revealed the cumulative effects of cascade low-head dams in an urban river, and provided new insights into the trade-off between construction and decommissioning of low-head dams in urban river systems.

The background microbiota and sanitization agent drive the fate of Listeria monocytogenes in multispecies biofilms formed on a plasma-polymerized coating applied on stainless steel

The present study evaluates the anti-biofilm activity of a coating applied with an atmospheric-pressure plasma jet system on AISI 316 stainless steel (SS) against multispecies biofilms containing Listeria monocytogenes (using background microbiota from three different meat industries) using culture-dependent and culture-independent approaches. Also, the disinfection effectiveness and biofilm evolution after sanitization with two food industry biocides were assessed. The anti-biofilm activity of the coating against L. monocytogenes, observed on mono-species biofilms (p < 0.05), was lost on the multispecies biofilms developed for 7 days at 12 °C (p > 0.05), with L. monocytogenes counts ranging from 5.5 ± 0.7 to 6.1 ± 0.5 CFU/cm2 on the uncoated SS and from 4.4 ± 0.2 to 6.4 ± 0.5 CFU/cm2 on the coated SS. The taxonomic composition of the formed biofilms was highly dependent on the industry but not affected by the artificial inoculation with L. monocytogenes and the nature of the surface (coated vs uncoated SS). When L. monocytogenes was artificially inoculated, its growth was partially controlled in the biofilms developed, with the magnitude of this effect being lower (p < 0.05 on coated SS) for the industry with the lowest taxonomy richness and diversity (3.8 ± 0.2 CFU/cm2), as compared the other two sampled industries (2.4 ± 0.4 and 1.6 ± 0.2 CFU/cm2). The 15-min disinfection treatments with either sodium hypochlorite or peracetic acid at 0.5 % resulted in total viable and L. monocytogenes counts below the limit of detection in most cases, immediately after treatment. The subsequent incubation of the sanitized plates for another 7 days at 12 °C in fresh BHI media led to the development of biofilms with lower bacterial richness and alpha diversity, and higher beta diversity. Even though sodium hypochlorite was in general slightly less effective than peracetic acid immediately after application, it caused a stronger growth control (p < 0.05) of the naturally present L. monocytogenes on the multispecies biofilms developed. This finding highlights the importance of understanding the interspecific competitive relationships between the members of the background microbiota and L. monocytogenes for the long-term control of this pathogen in food processing facilities.

Temperature or competition: Which has more influence on Mediterranean ant communities?

Temperature and competition are two of the main factors determining ant community assemblages. Temperature may allow species to forage more or less efficiently throughout the day (in accordance with the maximum activity temperature of each species). Competition can be observed and quantified from species replacements occurring during resource exploitation. We studied the interspecific competitive interactions of ant communities from the Doñana Biological Reserve (southern Spain). Ants were sampled from pitfall traps and baits in three habitats with contrasted vegetation physiognomy (savin forest, pine forest, and dry scrubland). We measured the temperature during the competitive interactions between species and created a thermal competition index (TCI) to assess the relative contribution of temperature and numerical dominance to the competitive outcomes. Temperature had unequal effects on ant activity in each type of habitat, and modulated competitive interactions. The TCI showed that a species’ success during pair interactions (replacements at baits) was driven by the proportion of workers between the two competing species and by the species-specific effect of temperature (how advantageous the temperature change is for each species during bait replacement). During competitive interactions, the effect of temperature (higher values of TCI) and numeric supremacy (higher worker proportion) gave higher success probabilities. Interspecific competitive relationships in these Mediterranean ant communities are habitat dependent and greatly influenced by temperature.

Interspecific Competitive Relationships between Crop Components and Weeds in Mixed Cropped Faba Bean (Vicia Faba L.) with False Flax (Camelina Sativa Crantz)

Interspecific Competitive Relationships between Crop Components and Weeds in Mixed Cropped Faba Bean (Vicia Faba L.) with False Flax (Camelina Sativa Crantz)

植物功能群去除对高寒草甸群落结构、多样性及生产力的影响

群落中物种的丧失在干扰下普遍存在，但对生态系统过程和功能的影响仍存在较大不确定性。选取青藏高原东缘典型高寒草甸为对象，开展优势植物功能群的梯度去除试验，以模拟长期过牧干扰下物种的损失。经过连续两个生长季的功能群去除，我们对群落的物种组成、结构、多样性和生物量等特征进行了分析，探讨了上述指标的响应过程和机制。研究结果表明：（1）功能群的去除降低了群落高度，增加了物种均匀度，并显著影响了禾草、杂草优势比以及功能群多样性和优势度；（2）同时，去除操作显著减小了凋落物量与禾草生物量，并显著影响了群落地上生物量；（3）进一步分析还发现，禾草、莎草和杂草功能群之间存在显著的竞争关系，群落生产力主要取决于禾草功能群并随物种均匀度的增大而显著减小。上述结果表明，禾草在高寒草甸群落中占据竞争优势地位，植物功能群的损失主要通过改变种间竞争关系、引起有机物质丢失影响群落过程和功能。;Impacts of biodiversity loss on ecosystem dynamics and functioning have aroused considerable attention and controversies. Loss of plant species is common in natural assembled community, whereas the response of ecosystem process remains unclearly. The continuous overgrazing of livestock has resulted significant plant species loss, like palatable grass and sedge species in alpine meadow on the Qinghai-Tibet plateau. In this study, we conducted a plant removal experiment to simulate the species loss along retrogressive succession gradient of alpine meadow resulting from long term overgrazing. A typical alpine meadow located on the eastern edge of the plateau was selected as the object to conduct the removal manipulation. The study site was fenced in April 2014 after the long term moderate winter grazing of yaks to exclude grazing of herbivores. Six removal treatments including: remove no plant species, remove Grass, remove Grass and Sedge, remove all species, randomly remove 25% of community aboveground biomass, and randomly remove 50% of community aboveground biomass. In middle July 2014 and 2015, we removed aboveground part of specific plant species individuals in 1 m×1 m plots. In late July 2016, the community coverage, height, species composition, diversity indices and biomass were investigated based on 0.5 m×0.5 m quadrats to detect response of alpine meadow to the removal experiment. The results showed that (1) removal of plant functional group (PFG) decreased the weighted-average height of community, but had no significant effect on the cumulative coverage of community. (2) Removal manipulation significantly influenced the summed dominance ratio (SDR) of Grass and Forb group, while no significant for Sedge group. (3) Removal of PFG increased the species evenness, and significantly influenced PFG diversity and dominance, whereas showed no significant effects for other diversity indices. (4) Removal of PFG reduced the litter biomass and Grass biomass. Only the removal of all plant reduced the community aboveground biomass. (5) In addition, further analysis showed that the community aboveground biomass was mainly depending on the Grass group, and decreased significantly with the increase of species evenness. And significantly competitive relationships were found among Grass, Sedge and Forb groups. The results showed that Grass species in the alpine meadow community have the greatest competitive advantage, the loss of plant species could change the community properties by means of influencing the inter-specific competitive relationships and significant plant biomass loss. The successive long-term monitoring on the response of community functioning to plant species loss should be strengthened.

Competitive characteristics related to nitrogen utilization and calla lily growth in rubber–calla lily intercropping systems

In this study, we analyzed the interspecific competitive relationships and their effect on the growth and nitrogen (N) utilization characteristics of calla lilies in rubber–calla lily intercropping systems using root barrier and 15N tracer techniques. Our results showed that intercropping significantly inhibited calla lily growth and reduced nitrogen uptake. Nitrogen utilization efficiency was also reduced in the individual parts of calla lily plants, as well as on a whole-plant basis, as a result of competition with rubber trees for nitrogen. Furthermore, nitrogen uptake by calla lily from fertilizer was lower than that from soil, and the percentage of nitrogen taken up from the fertilizer and the nitrogen utilization efficiency calculated by the tracer method were lower than those calculated using the difference method. Our results demonstrated that there two ways in which interspecific competition for nutrients between calla lilies and rubber trees can be mitigated: (1)calla lilies use adaptive strategies (such as increased root length, increased root numbers, and enhanced dry matter allocation to roots) to maximize their nutrient access and (2) N fertilizer application.

山西五鹿山白皮松群落乔灌层的种间分离

The Wulu Mountains,a part of the Luliang Mountain Range,are situated at 36°23′45″—36°38′20″N,111°08′—111°18′E in western Shanxi Province,China.This area has a warm-temperate continental monsoon climate with abundant plant resources and high biodiversity.Appropriate conditions for the growth of Pinus bungeana Zucc.ex Endl.are limited within the Wulu Mountains which include only a part of the overall range of P.bungeana.Therefore,building nature reserves in which P.bungeana can be studied systematically is important both ecologically and academically,with the goal of studying this species in its warm temperate north China climate so it can be preserved in natural forests indefinitely. Interspecific relationships are an important factor affecting community composition,structure,function and dynamics.Interspecific segregation refers to the relative distributions of two or more related species.It reflects the degree of mixing of two species based on their interrelationships.For example,the less two species mix,the higher the degree of interspecific segregation exists. The segregation relationship between different species pairs can be helpful in revealing the phenomena of species interactions,community structure and dynamics.This relationship can be used to explore the impacts of environmental differences on species distribution.Practically,such study is the scientific foundation of species conservation,restoration and the reconstruction of degraded ecosystems. We established 55 quadrats within natural P.bungeana communities to study the intraspecific and interspecific competition relationships of nine tree species and patterns of interspecific segregation of all species in the tree and shrub layers of P.bungeana communities.Using ArcView GIS software and the nearest neighbor method,interspecific segregation was studied with an N × N nearest-neighbor contingency table,a 2 × 2 nearest-neighbor contingency sub-table,and Hegyi′s competition index model for the individual tree species. The results indicate:(1) most of the species pairs are randomly segregated(80%),some species pairs are positively segregated(16.19%),and only a few species pairs are negatively segregated(3.81%).(2) There are some differences among different species in the interspecific segregation of all species.The larger individuals representing dominant species in the communities tended to be positively segregated with the other large trees and shrubs,probably because of their stronger competitive vigor.For example,P.bungeana,which is the most common and dominant species of this community,was positively segregated from Platycladus orientalis,Quercus wutaishanica,Ulmus pumila,Syringa pubescens,Cotoneaster multiflorus,Sophora davidii,Viburnum mongolicum,the dominant species of this community.Negative segregation appeared between dominant species and companion species in the communities,such as P.bungeana and Populus davidiana,P.orientalis and F.vulgaris,S.microphylla and Salix wallichiana.This appeared to be caused by the fact the companion species had fewer individuals,lower coverage and similar habitat requirements to the dominant species.Intensive interspecific competition resulted in a mosaic distribution and full competitive exploitation of resources among species,apparently causing them to be more likely to become negatively segregated. The 15 species from the forest plots were divided into three ecological species groups(ESG),based on their niches and relationships between the species,other plants and the environment.(3) The status of interspecific segregation of species has a close relationship to their intraspecific and interspecific competitive relationships and spatial distribution patterns.The larger individuals representing dominant species with more severe intraspecific competition than interspecific competition and appearing to have an aggregating distribution in the communities tended to be positively aggregated with the other large trees and shrubs.Negative aggregation(segregation) appeared between dominant species and companion species which have more severe interspecific competition than intraspecific competition in the communities.The interspecific competition of species within the same ESGs was more intense than in species in different ESGs.(4) The interspecific segregation is related to the heterogeneity in the communities,in that aggregation often occurs between two species which have different habitat requirements;while the segregation often appears between two species which have same or similar environmentally requirements.(5) The results show the 15 species we studied overlapped in distribution and were characterized by overall non-segregation.(6) The intraspecific and interspecific relationships were caused by ecological niches to which the different species are adapted and their biological requirements,and these differences may be the mechanisms which allow these species to stably coexist in the P.bungeana community of the Wulu Mountain Nature Reserve.

Direct physiological effects of nitrogen on Sphagnum: a greenhouse experiment

Summary1. Bogs are nutrient‐poor peatland ecosystems that are sensitive to nitrogen (N) deposition. Production of peat mosses (i.e. the peat‐forming genus Sphagnum) is known to decrease under elevated N deposition, but the causal mechanisms are poorly understood.2. It is predicted that increased N deposition will cause changes in Sphagnum species composition, with fast‐growing species benefiting from increased N availability in contrast to slow‐growing species. Knowledge of species‐specific responses to N availability can help us to understand interspecific competitive relationships.3. We investigated the direct effects of N application on plant physiology in three Sphagnum species by exposing shoots to a range of N doses (corresponding to depositions of 0–5·6 g m−2 year−1), over 5 months, in a greenhouse experiment. The species investigated included one that grows high above the water‐table (Sphagnum fuscum) and two that grow lower down (Sphagnum balticum and Sphagnum fallax). S. fuscum and S. balticum originate from ombrotrophic and S. fallax from minerotrophic environments. To estimate N responses, we measured the performance and light‐capture kinetics of the photosynthetic apparatus (maximum photosynthetic rate and Fv/Fm), biomass production, shoot formation, and N and phosphorus (P) concentrations in the tissue.4. Tissue nitrogen concentration generally increased with N application rate, and photosynthetic rate increased with N concentration, although S. balticum exhibited a unimodal response. With respect to production, a negative response to N application rate was found in S. fallax and S. fuscum (weak), while production in S. balticum was unrelated to application rate. S. fallax was the fastest‐growing species, producing two to three times more biomass per shoot compared with the other species.5. The mismatch between photosynthetic capacity and production could partly be explained by an increased N : P ratio following N application. Phosphorus limitation may not negatively affect photosynthetic capacity, but may hamper production.6. The fast‐growing species S. fallax is considered to benefit from increased N deposition, but we found a negative physiological response, suggesting stoichiometric constraints. Thus, we conclude that responses to N deposition cannot be predicted in a simple way from physiological traits related to growth rate without considering local environmental factors.

Niches and Interspecific Competitive Relationships of the Parasitoids,Microplitis prodeniaeandCampoletis chlorldeae, of the Oriental Leafworm Moth,Spodoptera litura, in Tobacco

Both Microplitis prodeniae Rao and Chandry (Hymenoptera: Bracondidae) and Campoletis chlorideae Uchida (Hymenoptera: Ichnumonidae) are major parasitoids of Spodoptera litura (Fabricious) (Lepidoptera: Noctuidae) in tobacco, Nicotiana tabacum L. (Solanales: Solanaceae) at Nanxiong, Guangdong Province, South China. The niches and interspecific competition relationships of the two species were studied. The results show that the competition between the two species for spatial and food resources was very intense, and C. chlorideae was always dominant when the two species compete for spatial and food resources in different periods. Thus C. chlorideae may drive M. prodeniae away when they occupy the same spatial or food resource. The adaptability of C. chlorideae to the environment in the tobacco fields may be greater than that of M. prodeniae, so C. chlorideae can maintain a higher population compared to that of M. prodeniae.

Relações interespecíficas entre parasitoides nativos de moscas-das-frutas e o braconídeo exótico Diachasmimorpha longicaudata em frutos de 'umbu-cajá'

Espécies de vespas parasitoides (Hymenoptera: Braconidae) são importantes agentes de controle biológico de moscas-das-frutas (Diptera: Tephritidae). Este trabalho teve por objetivo conhecer os efeitos da liberação e as relações de competitividade interespecífica do parasitoide exótico Diachasmimorpha longicaudata Ashmead sobre o complexo de parasitoides nativos de moscas-das-frutas associado a frutos de 'umbu-cajá' (Spondias spp.) na região do Recôncavo Baiano. Entre os meses de abril e julho de 2006, 8.955 frutos (192,93kg) foram coletados antes e após (24 e 48 horas) a liberação de 9.600 fêmeas de D. longicaudata em campo. Obteve-se um total de 8.724 pupários de Tephritidae, dos quais emergiram 3.963 adultos de Anastrepha obliqua (Macquart) e 1.115 parasitoides. A maior frequência relativa foi de Doryctobracon areolatus (Szépligeti), seguida por Asobara Anastrephae (Muesebeck) e Utetes Anastrephae (Viereck). Após 24 e 48 horas da liberação do parasitoide exótico D. longicaudata em campo, constatou-se que o índice de parasitismo total aumentou de 15,86 para 20,4 e 45,19%, respectivamente. Assim, observou-se que a liberação da espécie exótica D. longicaudata não apresenta efeitos negativos na ocorrência dos parasitoides nativos e contribui para complementar o controle biológico natural de A. obliqua em frutos de 'umbu-cajá', nas condições deste estudo.

Simulated Environmental Change Has Contrasting Effects on Defensive Compound Concentration in Three Alpine Plant Species

Environmental change, caused by nitrogen deposition and temperature increase, is predicted to affect allocation to carbon-based secondary compounds (CBSCs) in plants, due to changes in their internal carbon resources. The CBSCs are considered important for plant resistance to biotic and abiotic environmental stresses, such as herbivory, pathogen attacks, and UV radiation. To determine how allocation to putative defense compounds is affected by N deposition and increased temperature, we analyzed the composition of CBSCs in leaves of three arctic-alpine plant species: Bistorta vivipara, Dryas octopetala, and Salix reticulata after 5 years of warming (by open-top chambers) and experimental nutrient addition in an alpine Dryas heath in southern Norway. The dry weight of leaves increased after nutrient addition and warming combined with nutrient addition in all three species, while the weight of D. octopetala leaves also increased with warming alone. Individual chemical compounds or compound groups reacted to the treatments to different degrees and in different directions in the three species. The total concentration of CBSCs changed significantly only in S. reticulata, where it decreased in plots with nutrient addition combined with warming. Shading caused by taller vegetation in these plots might have bigger effects on the CBSC concentration than the direct changes in nutrient availability and temperature. Dryas octopetala had the highest concentration of CBSCs among the three species and was least affected by the treatments. Our results show that increased N availability and temperature influenced the level of carbon-based defense in some alpine plants but not others, indicating species-specific C-allocation responses to environmental change. Consequently, environmental changes may differentially affect defense abilities of alpine plant species, which could possibly contribute to future changes in interspecific competitive relationships and subsequently species composition of alpine plant communities.

Shoot and root competition in potato/maize intercropping: Effects on growth and yield

Interspecific competitive relationships and their effect on yield have been analysed in the association of potato and maize, two species with contrasting patterns of root and shoot systems establishment. Greenhouse experiments were carried out under three configurations (NC: no interspecific competition; FC: shoot and root interspecific competition; SC: shoot-only interspecific competition). Despite large variations between replicate experiments associated with seasonal effects, the study revealed consistent patterns of competition for above- and below-ground resources. Light interception in FC and SC was dominated by potato (60%) during the first 45 days after planting and by maize thereafter (80%). The extra shade caused by the companion crop increased soil moisture by up to 10% in SC treatments. The yield of the two species responded in opposite ways to SC, which was consistent with asymmetric patterns of competition between the two species. In potato, FC reduced tuber yield (number and size) by 4–26%, while SC increased tuber size (compared to NC) by 3–39%. In maize, FC reduced LAI and plant height by up to 45%, shoot and root dry mass, nutrient content, yield, the weight of 100 grains and harvest index by ca. 30–100%, while SC affected all but LAI and plant height. It appears that the contrast between the progressive installation of the maize root system and the rapid early extension of the potato root system is amplified by the restriction of maize root development under competition, which leads to close interdependencies between root and shoot competitive relationships. Although the specific effects of root competition cannot be uncovered by this set of experiments, competition effects on maize in the potato/maize intercropping seem to primarily related to light availability in the mixed canopy.

The Structure of Ant Assemblages in an Urban Area of Helsinki, Southern Finland

We collected ants in ten replicated habitat types of an urban island and described their assemblages using Non-metric Multidimensional Scaling and Multivariate Regression Trees. Lasius niger was the most abundant species, followed by Myrmica rubra, Formica fusca, L. flavus and L. platythorax; these species comprised 87% of all 1133 nests of the 16 species found. Ant assemblages changed gradually from open habitats to sites with closed tree canopy. Species most tolerant to urban pressure were L. niger, L. flavus and M. rugulosa, whereas forest-associated species were scarce or absent. Successful urban species had extensive (Palaearctic) or more limited (Euro-Siberian) distribution. Common and abundant habitat generalists were overrepresented relative to rural areas; these were also efficiently dispersing pioneer species with independent colony founding. Lack of suitable (micro)habitat apparently hampered colonization of many species. Competitively superior, territorial species were rare or absent, as were species dependent on dead wood, and many species depending on other ants. The indicated reorganization of interspecific competitive relationships may be due to selective impoverishment of the urban species pool. Comparison with other urban studies suggested that in ants, faunal homogenization has not taken place on a European scale.

Patch use as an indicator of habitat preference, predation risk, and competition

A technique for using patch giving up densities to investigate habitat preferences, predation risk, and interspecific competitive relationships is theoretically analyzed and empirically investigated. Giving up densities, the density of resources within a patch at which an individual ceases foraging, provide considerably more information than simply the amount of resources harvested. The giving up density of a forager, which is behaving optimally, should correspond to a harvest rate that just balances the metabolic costs of foraging, the predation cost of foraging, and the missed opportunity cost of not engaging in alternative activities. In addition, changes in giving up densities in response to climatic factors, predation risk, and missed opportunities can be used to test the model and to examine the consistency of the foragers' behavior. The technique was applied to a community of four Arizonan granivorous rodents (Perognathus amplus, Dipodomys merriami, Ammospermophilus harrisii, and Spermophilus tereticaudus). Aluminum trays filled with 3 grams of millet seeds mixed into 3 liters of sifted soil provided resource patches. The seeds remaining following a night or day of foraging were used to determine the giving up density, and footprints in the sifted sand indicated the identity of the forager. Giving up densities consistently differed in response to forager species, microhabitat (bush versus open), data, and station. The data also provide useful information regarding the relative foraging efficiencies and microhabitat preferences of the coexisting rodent species.