Interspecific Interference Research Articles

Spatial patterns of grassland–shrubland state transitions: a 74‐year record on grazed and protected areas.

Tree and shrub abundance has increased in many grasslands causing changes in ecosystem carbon and nitrogen pools that are related to patterns of woody plant distribution. However, with regard to spatial patterns of shrub proliferation, little is known about how they are influenced by grazing or the extent to which they are influenced by intraspecific interactions. We addressed these questions by quantifying changes in the spatial distribution of Prosopis velutina (mesquite) shrubs over 74 years on grazed and protected grasslands. Livestock are effective agents of mesquite dispersal and mesquite plants have lateral roots extending well beyond the canopy. We therefore hypothesized that mesquite distributions would be random on grazed areas mainly due to cattle dispersion and clustered on protected areas due to decreased dispersal and interspecific interference with grasses; and that clustered or random distributions at early stages of encroachment would give way to regular distributions as stands matured and density-dependent interactions intensified. Assessments in 1932, 1948, and 2006 supported the first hypothesis, but we found no support for the second. In fact, clustering intensified with time on the protected area and the pattern remained random on the grazed site. Although shrub density increased on both areas between 1932 and 2006, we saw no progression toward a regular distribution indicative of density-dependent interactions. We propose that processes related to seed dispersal, grass–shrub seedling interactions, and hydrological constraints on shrub size interact to determine vegetation structure in grassland-to-shrubland state changes with implications for ecosystem function and management.

Pairwise interactions between functional groups improve biological control

Ecologists have long debated whether predators primarily disrupt one another’s prey capture through interspecific interference, or instead complement one another by occupying different feeding niches. Resolution of this debate has been difficult because different experimental designs are typically used to study interference versus complementarity. We adopted a somewhat atypical approach, surveying communities of predatory insects on 73 free-growing Brassica oleracea plants, and then re-constructing each community in field cages to measure its impact on aphid prey. The predator communities naturally varied in species composition, richness, and relative abundance; in our experiment we kept total predator density constant to avoid confounding effects of differing overall abundance. The predator communities’ impacts on aphids differed by >10-fold. Using a generalized linear model, we found that pairings of several predators in the community improved aphid suppression while no pairings disrupted it. Indeed, accounting for the presence of the beneficial pairings provided more power than species richness to explain predators’ impacts on aphids. Altogether, our results suggest generally complementary or neutral, rather than disruptive, multi-predator effects in this community. Our approach may be useful for determining the frequency of complementary species-pairings in many other systems.

Does character displacement demonstrate density-dependent expression in females? A test on the wing shape of two species of European damselflies

Character displacement (CD) is the evolutionary process which leads to the divergence in trait expression of closely related species in regions where species co-occur, compared to allopatric populations. In Europe CD has been investigated in males of Calopteryx splendens and C. virgo and has been related to species recognition. If species recognition is relevant for males, also females should benefit from CD. The most obvious differences between females of these two species are wing profile and colour. We sampled females from allopatric and from sympatric populations with different relative abundances of these species. Wing shape and pigmentation were evaluated for each damselfly. CD was found in wing profile but not in wing transparency. The relative abundance of species significantly affected CD, but with a different pattern in each species. The prediction that wing shape become more different from the allopatric state when the species was relatively rare, but more similar to the allopatric state when the species was common was evident only for C. splendens. Wing shape changes might increase differences in flying patterns making males more effective to discriminate between heterospecific females. So, CD we observed may be the result of a selection directed to reduce interspecific reproductive interference.

Rye–Vetch Mixture Proportion Tradeoffs: Cover Crop Productivity, Nitrogen Accumulation, and Weed Suppression

Cereal–legume cover crop mixtures have the potential to combine the unique strengths of the component species while taking advantage of interspecific synergies. However, the relative proportion of each species in the mixture is likely to influence species interactions and entail important tradeoffs in cover crop performance. The objective of this study was to evaluate how the relative proportions of cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) sown in mixtures influenced cover crop biomass production, winter annual weed suppression, vetch winter survival, and vetch N2 fixation as measured by the 15N natural abundance method. Following a replacement series design, treatments consisted of a gradient of seven rye–vetch mixture proportions ranging from 100% vetch to 100% rye. Density and biomass composition in the mixtures were highly correlated with rye and vetch seeding rates, with little evidence of substantial interspecific interference. Total shoot biomass in all mixtures was equal to or greater than that of either monoculture, but no differences were detected in vetch winter survival or the efficiency of N2 fixation. Changing the proportions of rye and vetch in the mixtures resulted in tradeoffs related to N and weed management goals. Increasing vetch in mixtures led to greater fixed N accumulation but also increased seed costs and reduced winter annual weed suppression. A greater understanding of how rye–vetch mixture proportions influence cover crop performance can support more‐informed decision‐making regarding cover crop selection and mixture seeding rates.

The Effect of Phosphorus Reduction and Competition on Invasive Lemnids: Life Traits and Nutrient Uptake

Introduction of invasive macrophytes often leads to competition with native species or with already established invasive species. Competition between invasive species in multiple-invaded systems is expected to be particularly high, especially when they share growth form and position in the water column. We performed indoor experiments between invasive free-floating Lemna minuta and Landoltia punctata in monocultures and mixtures under a phosphorus gradient concurring with hypereutrophic, eutrophic, mesotrophic, and oligotrophic conditions. Our results showed that a phosphorus reduction from hypereutrophic to eutrophic had important negative impacts on the relative growth rate (RGR) of both species. A further reduction to mesotrophic condition did not alter either species RGR. However, species strategies and nutrient uptake differed. Both intra- and interspecific interference occurred; however, the intensity differed between phosphorus concentrations. Difference in RGR (RGRD) showed L. minuta to gain at high phosphorus levels, while a reduction favoured L. punctata. In oligotrophic condition, either species hardly produced new daughter fronds. Our results are useful to (1) understand the effects of phosphorus and setting target values in the process of eutrophication reduction and (2) diminish the impacts of invasive lemnids since a water column phosphorus reduction would prevent large impacts.

Awakened Oscillations in Coupled Consumer-Resource Pairs

The paper concerns two interacting consumer-resource pairs based on chemostat-like equations under the assumption that the dynamics of the resource is considerably slower than that of the consumer. The presence of two different time scales enables to carry out a fairly complete analysis of the problem. This is done by treating consumers and resources in the coupled system as fast-scale and slow-scale variables, respectively, and subsequently considering developments in phase planes of these variables, fast and slow, as if they are independent. When uncoupled, each pair has unique asymptotically stable steady state and no self-sustained oscillatory behavior (although damped oscillations about the equilibrium are admitted). When the consumer-resource pairs are weakly coupled through direct reciprocal inhibition of consumers, the whole system exhibits self-sustained relaxation oscillations with a period that can be significantly longer than intrinsic relaxation time of either pair. It is shown that the model equations adequately describe locally linked consumer-resource systems of quite different nature: living populations under interspecific interference competition and lasers coupled via their cavity losses.

How competitive trade-offs limit elevation ranges for temperate-breeding hummingbirds

One intriguing hypothesis about range limits of species along environmental gradients is that interspecific interference competition limits the activity of the better exploitation competitor. The hypothesis works if the costs of interference and (or) exploitation vary along the gradient. However, in some systems, species turnover happens over gradients that may be too short to induce changes in costs associated with competition. An example is breeding Black-chinned Hummingbirds (Archilochus alexandri (Bourcier and Mulsant, 1846)) and Broad-tailed Hummingbirds (Selasphorus platycercus (Swainson, 1827)) in western Colorado, USA, where turnover happens over ∼400 m. We recorded foraging and chasing activity of the two species at feeders and found that their foraging activity changed with elevation but interspecific competition did not. Because the foraging activity of the two species changed inversely with each other, it may be the presence of Black-chinned Hummingbirds rather than active interference that limits the activity of Broad-tailed Hummingbirds. Importantly, the relationship between foraging activity and elevation depended on the distance between the two feeders, which shows that relationships with elevation are contingent on other factors such as spatial distribution of resources. Our results suggest that interspecific differences in flight performance are not manifested over the short elevation gradient and do not account for changes in activity. Flight performance may indirectly affect patterns in breeding-season activity by influencing how species interact with other competitors during the nonbreeding season.

Crown modeling by terrestrial laser scanning as an approach to assess the effect of aboveground intra- and interspecific competition on tree growth

Individual tree growth is controlled by numerous factors, but intertree competition is of special importance as it is the only parameter that can be managed by silvicultural measures. Many indices dealing with aboveground interference use geometric standard crown shapes to quantify the competitive strength of neighbors on the target tree. As such crowns do not realistically represent the spatial heterogeneity in the canopy, a terrestrial laser scanner was used to gain detailed information on crown characteristics which may be used for a more precise modeling of the relationship between competition and growth. We examined groups of 5 trees growing in three major geographic regions of Germany to investigate the effect of intra- and interspecific competition for light on basal area growth of target beech trees (Fagus sylvatica). A competition index based on individual crown shapes derived from TLS-data correlated better with target tree growth than an index using conventional geometric crown shape models. Both measures ascribed the highest competitive strength to intraspecific competition. In contrast to the valuable hardwoods for which a slightly lower crown competition was calculated, the conifer species Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) had considerably weaker competitive effects on beech. The growth response of the investigated target trees reflected the strength in competition (highest relative basal area growth of beech if mixed with Scots pine>Norway spruce>valuable hardwoods>intraspecific competition) even though the increment measurements with self-acting dendrometers covered only one vegetation period. Neighborhood diversity and target tree growth were correlated, indicating stronger effects of intra- compared to interspecific interference. The utilization of a terrestrial laser scanner provided insights into canopy structure of the competitive neighborhood that may enhance our understanding of competitive interactions.

Predator Diversity Effects in an Exotic Freshwater Food Web

Cascading trophic interactions are often defined as the indirect effects of a predator on primary producers through the effect of the predator on herbivores. These effects can be both direct through removal of herbivores [density-mediated indirect interactions (DMIIs)] or indirect through changes in the behavior of the herbivores [trait-mediated indirect interactions (TMIIs)]. How the relative importance of these two indirect interactions varies with predator diversity remains poorly understood. We tested the effect of predator diversity on both TMIIs and DMIIs on phytoplankton using two competitive invasive dreissenid mussel species (zebra mussel and quagga mussel) as the herbivores and combinations of one, two or all three species of the predators pumpkinseed sunfish, round goby, and rusty crayfish. Predators had either direct access to mussels and induced both TMII and DMII, or no direct access and induced only TMII through the presence of risk cues. In both sets of treatments, the predators induced a trophic cascade which resulted in more phytoplankton remaining with predators present than with only mussels present. The trophic cascade was weaker in three-predator and two-predator treatments than in one-predator treatments when predators had direct access to dreissenids (DMIIs and TMIIs). Crayfish had higher cascading effects on phytoplankton than both pumpkinseed and round goby. Increased predator diversity decreased the strength of DMIIs but had no effect on the strength of TMIIs. The strength of TMIIs was higher with zebra than quagga mussels. Our study suggests that inter-specific interference among predators in multi-species treatments weakens the consumptive cascading effects of predation on lower trophic levels whereas the importance of predator diversity on trait mediated effects depends on predator identity.

Contrasting effects of the cyanobacterium Microcystis aeruginosa on the growth and physiology of two green algae, Oocystis marsonii and Scenedesmus obliquus, revealed by flow cytometry

Summary Aquatic photosynthetic productivity is influenced by resource availability, resource use efficiency and interspecific interactions. In hypertrophic environments, interspecific interference is known to influence species succession. The effect of interference by phytoplankton on biomass production is very poorly understood. One hypothesis is that the development of cyanobacterial blooms is triggered by the excretion of allelopathic substances that inhibit the growth of other phytoplankton species. In this study, we analysed how the co‐cultivation of the cyanobacterium Microcystis aeruginosa with two green algae (Oocystis marsonii and Scenedesmus obliquus) influences the resource use efficiency of each partner under nutrient‐replete conditions. Using single‐cell technologies, it was possible to quantify the efficiency of light use and the biomass gain for all three species under hypertrophic (non‐limiting nutrient) conditions. The presence of M. aeruginosa resulted in growth inhibition, reduced metabolic activity and an increased quantum requirement for biomass assimilation in O. marsonii, whereas no changes were observed in S. obliquus. M. aeruginosa, on the other hand, showed an increased cell size in mixed cultures with O. marsonii. However, with respect to biomass production, M. aeruginosa did not profit from the growth inhibition of O. marsonii in the experimental period of 8 days. By contrast, the co‐cultivation of M. aeruginosa with S. obliquus did not affect the physiological activity of either species. This study highlights the potential of flow cytometry to determine species‐specific basic growth parameters, light‐use efficiency and biomass gain during co‐cultivation of different algal strains. It is further demonstrated that sorted cells can be used to analyse their macromolecular composition. The results of this study reveal very different species‐specific patterns of growth kinetics and light‐use‐efficiency of green algae in co‐cultivation experiments with a cyanobacterium.

Effects of livestock and non-native mouflon on use of high-elevation pastures by Alpine chamois

Interspecific interference among livestock, native and non-native large herbivores is a key management and conservation issue, and little is known about its dynamics and implications. We investigated whether native Alpine chamois (Rupicapra r. rupicapra) modify their spatial distribution when non-native mouflon Ovis orientalis musimon and livestock (domestic sheep Ovis aries, and domestic goats Capra hircus) inhabit the same areas in the Alpine meadows of Italian Eastern Alps. We walked 5 hiking trails (5.0±0.1km) at dawn, twice a month during summers 2007 and 2008. During these surveys, we located each group of free-ranging ungulates (chamois, mouflon, and livestock). We also estimated the quality of meadows, finding that forage availability increased linearly as the distance from rocks (i.e., chamois refuges) increased. We predicted that the linear distance between chamois groups and rocks would depend on the co-presence of livestock and mouflon groups. Our results showed that chamois were more likely to be observed in areas with low food availability, but safer (i.e., closer to the rocks), whenever the nearest livestock group was larger and closer, especially if the shepherd's dog was present. Avoidance of the best feeding patches by the wild species is presumably due to spatial interference (e.g. visual and acoustic disturbance) and/or predation risk perception caused by the presence of shepherd's dogs. Similarly, the larger was the nearest group of mouflon, the closer to rocks was located the chamois group. Interestingly, mouflon group vicinity induced chamois to move closer to rocks only if mouflon rams were within the group. This suggests that physical displacement of the smaller species (i.e. chamois) is likely to occur to avoid direct disturbance of larger mouflon rams. Our study clearly showed how a native herbivorous species adjusts its spatial distribution and decreases the likelihood of using areas with higher food availability when livestock and/or a non-native species co-occur.

What makes a good neighborhood? Interaction of spatial scale and fruit density in the predator satiation dynamics of a masting juniper tree

Spatio-temporal variability in fruit production (masting) has been regarded as a key mechanism to increase plant fitness by reducing seed predation. However, considerably more effort has been devoted into understanding the consequences of temporal rather than spatial variations in fruit crop for plant fitness. In order to simultaneously evaluate both components, we quantify fruit production and pre-dispersal damage by three arthropod species (mites, chalcid wasps and moths) in the Spanish juniper (Juniperus thurifera) during 3 years in a spatially explicit context. Our aims were to assess (1) the interaction between fruit production and pre-dispersal fruit damage by arthropods, (2) the potential interference or competition between arthropods, and (3) the form of the phenotypic selection exerted by arthropods on fruit traits considering the spatial context. Arthropods damaged a substantial fraction of fruits produced by Spanish juniper with levels of damage showing sharp inter-annual variations. Fruit damage by mites was negatively related to yearly fruit crop and positively correlated at individual trees fruiting in consecutive years. Increased interspecific interference was an additional consequence of reduced fruit availability during small crop years. During a masting year, fruit damage by less mobile species such as mites was negatively affected by tree crop size, and no spatial structure was observed for mite damage. The incidence of chalcid wasps was low, so the spatial pattern of seed predation was unclear, and no preferences for fruit or seed traits were detected. Conversely, moths selected larger fruits and their incidence on trees was spatially aggregated up to 20 m, with predation levels being negatively affected by fruit abundance at the patch level, suggesting a positive density-dependent effect of neighbors on fruit output. These results highlight the importance of including the spatial component to understand complex species interactions at local scales.

Strategies of the invasive macrophyte Ludwigia grandiflora in its introduced range: Competition, facilitation or coexistence with native and exotic species?

The success of invasive species is due to their ability to displace other species by direct competition. Our hypothesis is that the strategy of the invasive L. grandiflora differs according to the growth form of this plant (submerged/emergent) and to its density, and the presence and the density of neighbouring species, during the first step of introduction phase. Moreover, we also suppose that the invasive species L. grandiflora affects the European native aquatic macrophyte and that invasive species can facilitate the establishment, growth and spread of exotic species coming from the same biogeographical area (the “Invasional Meltdown Hypothesis”). We studied the relationships between three exotic species coming from South America (Ludwigia grandiflora, Egeria densa and Myriophyllum aquaticum) and two European macrophyte species (Ceratophyllum demersum, Mentha aquatica) in monocultures and in mixed cultures. The experiments were carried out in containers placed in a greenhouse for one month in spring 2011. We measured six morphological traits to test the intraspecific and interspecific interferences. In accordance with our hypothesis, the strategy of L. grandiflora differed between its emergent growth form and its submerged growth form, whereas the establishment and the growth of L. grandiflora did not seem to be facilitated by other exotic species (i.e. E. densa and M. aquaticum). The interspecific effect between C. demersum or E. densa on submerged L. grandiflora was stronger in inhibiting plant growth than the intraspecific interferences of L. grandiflora on itself. Mutual inhibition of root production and growth was observed between L. grandiflora and M. aquatica. However, L. grandiflora seemed to have little impact on native species, which may coexist with L. grandiflora during the early stages of L. grandiflora establishment in the introduction area. L. grandiflora stimulated the growth and the vegetative reproduction of E. densa. L. grandiflora facilitated the establishment of E.densa in accordance with the “Invasional Meltdown Hypothesis”. L. grandiflora stimulated the root production and the growth of M. aquaticum at low densities and inhibited it at high densities. L. grandiflora, the first introduced plant in France, could slightly facilitate the growth of E. densa. However, spatial heterogeneity or differential use of resources could explain the coexistence of L. grandiflora and M. aquaticum in the same environment.

Differential behavioural and endocrine responses of common voles (Microtus arvalis) to nest predators and resource competitors

BackgroundAdaptive behavioural strategies promoting co-occurrence of competing species are known to result from a sympatric evolutionary past. Strategies should be different for indirect resource competition (exploitation, e.g., foraging and avoidance behaviour) than for direct interspecific interference (e.g., aggression, vigilance, and nest guarding). We studied the effects of resource competition and nest predation in sympatric small mammal species using semi-fossorial voles and shrews, which prey on vole offspring during their sensitive nestling phase. Experiments were conducted in caged outdoor enclosures. Focus common vole mothers (Microtus arvalis) were either caged with a greater white-toothed shrew (Crocidura russula) as a potential nest predator, with an herbivorous field vole (Microtus agrestis) as a heterospecific resource competitor, or with a conspecific resource competitor.ResultsWe studied behavioural adaptations of vole mothers during pregnancy, parturition, and early lactation, specifically modifications of the burrow architecture and activity at burrow entrances. Further, we measured pre- and postpartum faecal corticosterone metabolites (FCMs) of mothers to test for elevated stress hormone levels. Only in the presence of the nest predator were prepartum FCMs elevated, but we found no loss of vole nestlings and no differences in nestling body weight in the presence of the nest predator or the heterospecific resource competitor. Although the presence of both the shrew and the field vole induced prepartum modifications to the burrow architecture, only nest predators caused an increase in vigilance time at burrow entrances during the sensitive nestling phase.ConclusionVoles displayed an adequate behavioural response for both resource competitors and nest predators. They modified burrow architecture to improve nest guarding and increased their vigilance at burrow entrances to enhance offspring survival chances. Our study revealed differential behavioural adaptations to resource competitors and nest predators.

Coexistence periodic solutions of a doubly nonlinear parabolic system with Neumann boundary conditions

This paper is concerned with a competitive and cooperative mathematical model for two biological populations which dislike crowding, diffuse slowly and live in a common territory under different kind of intra- and inter-specific interferences. The model consists of a system of two doubly nonlinear parabolic equations with nonlocal terms and Neumann boundary conditions. Based on the theory of the Leray–Schauder degree, we obtain the coexistence periodic solutions, namely the existence of two non-trivial non-negative periodic solutions representing the densities of the two interacting populations, under different intra- and inter-specific interferences on their natural growth rates.

Behavioral Interference Between Sympatric Reindeer and Domesticated Sheep in Norway

Abstract Interspecific interaction among sympatric ungulates is important in management and conservation. We investigated behavioral interference between sympatric wild or semidomestic reindeer ( Rangifer tarandus tarandus ) and sheep ( Ovis aries ) in two field studies and one enclosure experiment. For free-ranging wild and semidomestic reindeer, interference between the two species increased with decreasing distances, occurring only at less than 200 m and 30 m, for wild and semidomestic reindeer, respectively, and neither species consistently dominated the other. In a controlled, duplicated experiment we tested interference and confrontations at the feeding patch level among semidomestic reindeer and sheep within 40 × 50 m enclosures. When new reindeer or sheep were introduced into enclosures already occupied by reindeer, new reindeer resulted in significantly more interference and confrontations among individuals compared to new sheep; i.e., intraspecific interference was more prevalent than interspecific interference at equal densities. For all study areas, confrontations decreased with time after “first encounter,” indicating cohabituation. A sympatric use of pastures was not visually disruptive for recorded grazing behavior for either species.

Early interspecific interference in the wheat/faba bean (Triticum aestivum/ Vicia faba ssp. minor) and rapeseed/squarrosum clover (Brassica napus var. oleifera/Trifolium squarrosum) intercrops

Most of research on intercrops evaluate performances and interference between species on the basis of final yield, while little knowledge is available on the interference in early stages and at the root level, at least for cultivated intercrops. In fact, in the few studies on this subject species are often combined minding at experimental needs ( e.g. common substrate, temperature and water requirements, easy root separation) more than at their actual use in the farm. The present work evaluates interspecific interference during early developmental stages for two intercrops of agricultural interest: soft wheat-faba bean and rapeseed-squarrosum clover. Improving this knowledge would help intercrop growth modelling and rational cultivation. The experiments were carried out on soft wheat ( Triticum aestivum ), faba bean ( Vicia faba var. minor ), rapeseed ( Brassica napus var. oleifera ) and squarrosum clover ( Trifolium squarrosum ), germinated and grown until 32 days after sowing (DAS) as one-species stands or as wheat/faba bean and rapeseed/squarrosum clover intercrops, with different densities and proportions for the two species in each couple. Germination was studied in controlled-temperature chamber, plantlet growth was studied on pots in the greenhouse. During germination no interspecific interference was observed for both wheat/faba bean and rapeseed/squarrosum clover intercrops. During plantlet growth, interspecific interference occurred in both intercrops causing variations in whole plant and root dry matter accumulation. In the wheat/faba bean intercrop each species suffered from the competitive effect of the companion species and faba bean was the dominant species when present in lower proportion than wheat. The unexpectedly high aggressivity of faba bean may be explained either with the greater seed size that could have represented an initial advantage within the short duration of the experiment or with the competition towards wheat for substrate N which is not usual in the open field for a N fixing species. In the rapeseed/squarrosum clover intercrop, rapeseed was facilitated by squarrosum clover, while squarrosum clover suffered from the competitive effect of rapeseed, which was the dominant species. The resource use efficiency of intercrops as compared to that of one-species crops was lower in the wheat/faba bean couple, not much different in the rapeseed/squarrosum clover one. In both couples, the best performance was observed when the ratio of the dominant species was lower than that of the companion species (number of plants in the ratio 1:3).

Coexistence via resource partitioning fails to generate an increase in community function.

Classic ecological theory suggests that resource partitioning facilitates the coexistence of species by reducing inter-specific competition. A byproduct of this process is an increase in overall community function, because a greater spectrum of resources can be used. In contrast, coexistence facilitated by neutral mechanisms is not expected to increase function. We studied coexistence in laboratory microcosms of the bactivorous ciliates Paramecium aurelia and Colpidium striatum to understand the relationship between function and coexistence mechanism. We quantified population and community-level function (biomass and oxygen consumption), competitive interactions, and resource partitioning. The two ciliates partitioned their bacterial resource along a size axis, with the larger ciliate consuming larger bacteria than the smaller ciliate. Despite this, there was no gain in function at the community level for either biomass or oxygen consumption, and competitive effects were symmetrical within and between species. Because other potential coexistence mechanisms can be ruled out, it is likely that inter-specific interference competition diminished the expected gain in function generated by resource partitioning, leading to a system that appeared competitively neutral even when structured by niche partitioning. We also analyzed several previous studies where two species of protists coexisted and found that the two-species communities showed a broad range of biomass levels relative to the single-species states.

同种或异种干扰对花鼠分散贮藏点选择的影响

Siberian chipmunks(Tamias sibiricus) tend to increase scatter-hoarding intensity in face of competitions posited by conspecifics and / or interspecifics;however,little is known how they deposit their caches in response to these competitions.Within outdoor enclosures,we investigated how Siberian chipmunks response to conspecifics(females and males) and interspecifics(Korean field mice,Apodemus peninsulae) in cache site selection.We found:(1) Siberian chipmunks avoided to cache in the areas of high competitions in face of both conspecifics and interspecifics;(2) female chipmunks decreased to cache in the high competition areas,while males increased to cache in the median competition areas when conspecifics presented.These results suggest that when competition is high,Siberian chipmunks tend to reduce hoarding foods in the areas with high competition to avoid pilferage;however,males and females may response differently to conspecifics in cache site selection.

Under my wing: lesser kestrels and jackdaws derive reciprocal benefits in mixed-species colonies

In mixed-species assemblages, antipredator benefits for a timid species nesting close to a more pugnacious one are often reported. Advantages for the protected species are usually manifested in terms of higher reproductive success than conspecifics nesting remote to the protector species. Whether the protector species also accrues any benefit remains untested, and the species-specific behavioral traits underlying enhanced reproductive output in mixed-species associations remain poorly documented. We studied associations between lesser kestrels (Falco naumanni) and jackdaws (Corvus monedula) nesting in rural buildings in the Gela Plain (Italy). We tested for interspecific interactions of jackdaws and lesser kestrels by comparing single- and mixed-species colonies in terms of: 1) vigilance, nest attendance, and intra- and interspecific interference and 2) defensive responses shown by each species when confronted with potential predators or competitors. In both species, nesting in mixed associations was accompanied by decreased vigilance. Diminished vigilance, however, was associated with decreased defensive effort for lesser kestrels, whereas jackdaws increased alarm calling, but only in small colonies. Our results reveal a reciprocal influence on behavior of lesser kestrels and jackdaws nesting within the same colony, whereby both species experience decreased energetic expenditures associated with vigilance, but only lesser kestrels appear to benefit via reduced nest defense effort. We discuss our results in light of the possible asymmetrical information transfer triggered by a common set of nest predators that favors the exchange of interspecific information regarding predator detection and defense.