Asymmetric competition between larvae of the blowflies Calliphora vicina and Lucilia sericata in carrion

1. The relative abundance of the blowflies Calliphora vicina (R.-D.) and Lucilia sericata (Meigen) in carrion was considered in relation to inter- and intraspecific larval competition and the distribution of adults between habitat types. 2. In mixed and pure laboratory cultures of L. sericata and C. vicina the mortality of both species increased and adult size declined as the initial larval number was increased. However, for L. sericata at initial numbers greater than ten larvae/g of liver, the effects of competition on adult size and mortality were greater in the mixed cultures than in the pure cultures. In contrast, for C. vicina at numbers greater than ten larvae/g of liver, the effects of competition on adult size and mortality were greater in the pure cultures than in the mixed cultures. 3. The laboratory data suggest therefore that for L. sericata the effects of interspecific competition with C. vicina on size and mortality were greater than the effects of intraspecific competition in a pure culture at the same initial number. Notably, however, the intensity of interspecific competition was not sufficiently asymmetric to allow C. vicina to exclude L. sericata even at the highest numbers examined. 4. In the field, higher numbers of adult L. sericata emerged from the carcasses of laboratory mice placed in open pasture than in woodland or hedgerow sites. In contrast, higher numbers of C. vicina emerged from carcasses placed in woodland and hedgerow sites. 5. Trapping showed that in the field adult L. sericata were relatively more abundant in open pasture than in woodland and hedgerow sites, while C. vicina were more abundant in woodland and hedgerow sites than in open pasture. 6. It is concluded that the low numbers of L. sericata that emerge from carrion relative to the numbers of C. vicina may, in part, be the result of asymmetric interspecific competition, but that the uneven distribution of adults of the two species among habitat types also plays a major role in shaping the blowfly community in carrion.     

Kin selection,species richness and community

Can evolutionary and ecological dynamics operating at one level of the biological hierarchy affect the dynamics and structure at other levels? In social insects, strong hostility towards unrelated individuals can evolve as a kin-selected counter-adaptation to intraspecific social parasitism. This aggression in turn might cause intraspecific competition to predominate over interspecific competition, permitting coexistence with other social insect species. In other words, kin selection—a form of intra-population dynamics—might enhance the species richness of the community, a higher-level structure. The converse effect, from higher to lower levels, might also operate, whereby strong interspecific competition may limit the evolution of selfish individual traits. If the latter effect were to prove more important, it would challenge the common view that intra-population dynamics (via individual or gene selection) is the main driver of evolution.     

COMPETITION AND THE EVOLUTION OF AGGRESSIVE BEHAVIOR IN TWO SPECIES OF TERRESTRIAL SALAMANDERS

The effects of competition on the evolution of interspecific interference mechanisms were studied by comparing the aggressive behavior of two terrestrial salamander species from two localities that differ in the intensity of interspecific competition. Plethodon jordani and P. glutinosus are closely related, ecologically similar species that are sympatric at intermediate elevations in the southern Appalachian Mountains. Previous removal and transplant experiments showed that interspecific competition is more intense in the northeastern Great Smoky Mountains, where the species are narrowly sympatric, than in the nearby Balsam Mountains, where sympatry is broader. In laboratory encounters, P. glutinosus from the Great Smoky Mountains were more aggressive to heterospecific and conspecific intruders than were P. glutinosus from the Balsam Mountains. For P. jordani, however, the variation in interspecific and intraspecific aggressive behavior among individuals within populations was as great as the variation between populations. Alpha-selection (i.e., improved competitive ability by the acquisition of interspecific interference mechanisms) has occurred in populations of P. glutinosus under conditions of intense interspecific competition. The evolution of aggressive behavior appears to have been influenced by the intensity of intraspecific competition as well.     

Balearic lizards use chemical cues from a complex deceptive mimicry to capture attracted pollinators

Deceptive flowers from several plant species emit odors that mimic oviposition cues and attract female insects seeking for a laying site. Helicodiceros muscivorus is a species that emits an odor mimicking the foul smell of rotting meat and thereby attracts blowflies that usually oviposit on carcasses but are deceived into pollinating the plant. Thus, H. muscivorus is a striking case of pollination by brood‐site deception. The Balearic lizard, Podarcis lilfordi, exhibits remarkable interactions with dead horse arum. Balearic lizards, which sometimes forage on carcasses, are attracted to blooming dead horse arum. We showed experimentally that P. lilfordi can detect chemical cues from carcasses on cotton swabs and exhibits elevated tongue‐flick rates to carcass chemical cues compared to control stimuli. Lizards also detected and located hidden carcasses using only airborne chemical cues. The responses of lizards to chemical cues from the spadix of blooming dead horse arum were qualitatively and quantitatively similar to those to carcass odors. Therefore, the decay‐like odor that attracts blowflies for the plant's benefit also attracts lizards. This attraction may initially have been somewhat favorable for lizards that eat blowflies, but slightly unfavorable for plants because the lizards ate some pollinators. We suggest that lizards attracted by odor may have learned later to use the plant for thermoregulation and then consume its fruits, making the association more positive for lizards and benefitted arum by seed dispersal.     

Contrasting forms of competition set elevational range limits of species

How abiotic and biotic factors constrain distribution limits at the harsh and benign edges of species ranges is hotly debated, partly because macroecological experiments testing the proximate causes of distribution limits are scarce. It has long been recognized – at least since Darwin’s On the Origin of Species – that a harsh climate strengthens competition and thus sets species range limits. Using thorough field manipulations along a large elevation gradient, we show the mechanisms by which temperature determines competition type, resulting in a transition from interference to exploitative competition from the lower to the upper elevation limits in burying beetles (Nicrophorus nepalensis). This transition is an example of Darwin’s classic hypothesis that benign climates favor direct competition for highly accessible resources while harsh climates result in competition through resources of high rivalry. We propose that identifying the properties of these key resources will provide a more predictive framework to understand the interplay between biotic and abiotic factors in determining geographic range limits.     

Kin selection and the evolution of social information use in animal conflict

Animals often use social information about conspecifics in making decisions about cooperation and conflict. While the importance of kin selection in the evolution of intraspecific cooperation and conflict is widely acknowledged, few studies have examined how relatedness influences the evolution of social information use. Here we specifically examine how relatedness affects the evolution of a stylised form of social information use known as eavesdropping. Eavesdropping involves individuals escalating conflicts with rivals observed to have lost their last encounter and avoiding fights with those seen to have won. We use a game theoretical model to examine how relatedness affects the evolution of eavesdropping, both when strategies are discrete and when they are continuous or mixed. We show that relatedness influences the evolution of eavesdropping, such that information use peaks at intermediate relatedness. Our study highlights the importance of considering kin selection when exploring the evolution of complex forms of information use.     

Coevolution of competing Callosobruchus species does not stabilize coexistence

Interspecific resource competition is expected to select for divergence in resource use, weakening interspecific relative to intraspecific competition, thus promoting stable coexistence. More broadly, because interspecific competition reduces fitness, any mechanism of interspecific competition should generate selection favoring traits that weaken interspecific competition. However, species also can adapt to competition by increasing their competitive ability, potentially destabilizing coexistence. We reared two species of bean beetles, the specialist Callosobruchus maculatus and the generalist C. chinensis, in allopatry and sympatry on a mixture of adzuki beans and lentils, and assayed mutual invasibility after four, eight, and twelve generations of evolution. Contrary to the expectation that coevolution of competitors will weaken interspecific competition, the rate of mutual invasibility did not differ between sympatry and allopatry. Rather, the invasion rate of C. chinensis, but not C. maculatus, increased with duration of evolution, as C. chinensis adapted to lentils without experiencing reduced adaptation to adzuki beans, and regardless of the presence or absence of C. maculatus. Our results highlight that evolutionary responses to interspecific competition promote stable coexistence only under specific conditions that can be difficult to produce in practice.     

Repression of competition favours cooperation: experimental evidence from bacteria

Repression of competition (RC) within social groups has been suggested as a key mechanism driving the evolution of cooperation, because it aligns the individual’s proximate interest with the interest of the group. Despite its enormous potential for explaining cooperation across all levels of biological organization, ranging from fair meiosis, to policing in insect societies, to sanctions in mutualistic interactions between species, there has been no direct experimental test of whether RC favours the spread of cooperators in a well‐mixed population with cheats. To address this, we carried out an experimental evolution study to test the effect of RC upon a cooperative trait – the production of iron‐scavenging siderophore molecules – in the bacterium Pseudomonas aeruginosa. We found that cooperation was favoured when competition between siderophore producers and nonsiderophore‐producing cheats was repressed, but not in a treatment where competition between the two strains was permitted. We further show that RC altered the cost of cooperation, but did not affect the relatedness among interacting individuals. This confirms that RC per se, as opposed to increased relatedness, has driven the observed increase in bacterial cooperation.     

The other facets of family life and their role in the evolution of animal sociality

Family life forms an integral part of the life history of species across the animal kingdom and plays a crucial role in the evolution of animal sociality. Our current understanding of family life, however, is almost exclusively based on studies that (i) focus on parental care and associated family interactions (such as those arising from sibling rivalry and parent‐offspring conflict), and (ii) investigate these phenomena in the advanced family systems of mammals, birds, and eusocial insects. Here, we argue that these historical biases have fostered the neglect of key processes shaping social life in ancestral family systems, and thus profoundly hamper our understanding of the (early) evolution of family life. Based on a comprehensive survey of the literature, we first illustrate that the strong focus on parental care in advanced social systems has deflected scrutiny of other important social processes such as sibling cooperation, parent–offspring competition and offspring assistance. We then show that accounting for these neglected processes – and their changing role over time – could profoundly alter our understanding of the origin and subsequent evolution of family life. Finally, we outline how this ‘diachronic’ perspective on the evolution of family living provides novel insights into general processes driving the evolution of animal sociality. Overall, we infer that the explicit consideration of thus‐far neglected facets of family life, together with their study across the whole diversity of family systems, are crucial to advance our understanding of the processes that shape the evolution of social life.     

Arbuscular mycorrhizal impacts on competitive interactions between Acacia etbaica and Boswellia papyrifera seedlings under drought stress

Aims Arbuscular mycorrhizal fungi can have a substantial effect on the water and nutrient uptake by plants and the competition between plants in harsh environments where resource availability comes in pulses. In this study we focus on interspecific competition between Acaia etbaica and Boswellia papyrifera that have distinctive resource acquisition strategies. We compared the extent of interspecific competition with that of intraspecific competition.Methods In a greenhouse study we examined the influence of Arbuscular Mycorrhiza (AM) and pulsed water availability on competitive interactions between seedlings of the rapidly growing species A. etbaica and the slowly growing species B. papyrifera. A factorial experimental design was used. The factors were AM, two water levels and five species combinationsImportant findings Seedlings of both species benefitted from AM when grown alone, and the positive growth response to pulsed water availability in B. papyrifera seedlings was in contrast with the negative growth response for A. etbaica seedlings. AM also affected the competitive performance of both species. B. papyrifera was not affected by intraspecific competition, whereas A. etbaica was negatively affected compared to the seedlings grown alone. This effect was stronger in the presence of AM. In interspecific competition, A. etbaica outcompeted B. papyrifera. Mycorrhiza and pulsed water availability did not affect the outcome of interspecific competition, and the aggressivity index of A. etbaica remained unchanged. The extent to which AM influences plant competition in a drought-stressed environment may depend on belowground functional traits of the species. AM and pulsed water availability could modify the balance between intraspecific and interspecific competition. By affecting the balance between intraspecific and interspecific competition, both factors could impact the establishment and survival of seedlings.     

Sexual conflict and ecology: Species composition and male density interact to reduce male mating harassment and increase female survival

Sexual conflict is a pervasive evolutionary force that can reduce female fitness. Experimental evolution studies in the laboratory might overestimate the importance of sexual conflict because the ecological conditions in such settings typically include only a single species. Here, we experimentally manipulated conspecific male density (high or low) and species composition (sympatric or allopatric) to investigate how ecological conditions affect female survival in a sexually dimorphic insect, the banded demoiselle (Calopteryx splendens). Female survival was strongly influenced by an interaction between male density and species composition. Specifically, at low conspecific male density, female survival increased in the presence of heterospecific males (C. virgo). Behavioral mating experiments showed that interspecific interference competition reduced conspecific male mating success with large females. These findings suggest that reproductive interference competition between con‐ and heterospecific males might indirectly facilitate female survival by reducing mating harassment from conspecific males. Hence, interspecific competitors can show contrasting effects on the two sexes thereby influencing sexual conflict dynamics. Our results call for incorporation of more ecological realism in sexual conflict research, particularly how local community context and reproductive interference competition between heterospecific males can affect female fitness.     

Presence of soldier larvae determines the outcome of competition in a polyembryonic wasp

Soldier‐producing polyembryonic waSPS are the only social animals that develop as parasites inside the bodies of other insects. Characterizing the kin composition of broods is central to understanding the evolution of the soldier caste in these unique social insects. Here we studied the role of soldiers in mediating the outcome of competition among clones of the polyembryonic wasp Copidosoma floridanum. Soldier‐producing female clones usually monopolized host resources, whereas soldierless male clones usually coexisted in hosts. Behavioural experiments further indicated that early‐emerging soldiers are specialized to combat intraspecific competitors and later‐emerging soldiers are specialized for defence against interspecific competitors. Taken together, our results point to intraspecific competition as a major selective force in the evolution of the soldier caste. Our data also present an evolutionary conundrum: given the benefit of soldiers, why are male clones functionally soldierless?     

Study of community assembly patterns and interspecific interactions involved in insect succession on rat carcasses

Although many forensic entomological studies have described patterns of carrion insect succession and theoretical studies have explained interspecific interactions that drive succession, empirical studies on the quantitative and ecological aspects of carrion insect succession, such as the degree of historical contingency in community assembly and interspecific interactions during succession, are limited. In this study, I investigated variability in the successional pathways of carrion insect communities in rat carcasses and their decomposition processes, and examined the interspecific interactions involved in succession, such as the effects of carcass utilization by early‐arriving species on late‐arriving species. Members of the families Calliphoridae and Formicidae and the species Eusilpha japonica (Motschulsky) and Nicrophorus concolor Kraatz were chiefly observed. In almost all carcasses, formicid species arrived first, and calliphorid species and E. japonica arrived simultaneously or immediately after. Nicrophorus concolor arrived last, with its time of colonization occurring earlier in carcasses with greater E. japonica abundance. Meanwhile, the early‐arriving species decreased when N. concolor arrived. Nicrophorus concolor tended to reproduce on carcasses with lower cumulative abundance of early‐arriving species and tended to feed on carcasses with greater cumulative abundance of early‐arriving species. These results show that the successional pathways of the chief carrion insect species are highly consistent among carcasses. In contrast, early‐arriving species seem to influence the utilization patterns of carcasses by late‐arriving species, and therefore produce variability in the decomposition process. These results also show that succession could be driven by facilitation and interspecific competition between early‐arriving and late‐arriving species.     

Community complexity drives patterns of natural selection on a chemical defense of Brassica nigra

Plants interact with many different species throughout their life cycle. Recent work has shown that the ecological effects of multispecies interactions are often not predictable from studies of the component pairwise interactions. Little is known about how multispecies interactions affect the evolution of ecologically important traits. We tested the direct and interactive effects of inter- and intraspecific competition, as well as of two abundant herbivore species (a generalist folivore and a specialist aphid), on the selective value of a defensive chemical compound in Brassica nigra. We found that investment in chemical defense was favored in interspecific competition but disfavored in intraspecific competition and that this pattern of selection was dependent on the presence of both herbivores, suggesting that selection will depend on the rarity or commonness of these species. These results show that the selective value of ecologically important traits depends on the complicated web of interactions present in diverse natural communities and that fluctuations in community composition may maintain genetic variation in such traits.     

What is macroevolution?

Definitions of macroevolution fall into three categories: (1) evolution of taxa of supraspecific rank; (2) evolution on the grand time-scale; and (3) evolution that is guided by sorting of interspecific variation (as opposed to sorting of intraspecific variation in microevolution). Here, it is argued that only definition 3 allows for a consistent separation of macroevolution and microevolution. Using this definition, speciation has both microevolutionary and macroevolutionary aspects: the process of morphological transformation is microevolutionary, but the variation among species that it produces is macroevolutionary, as is the rate at which speciation occurs. Selective agents may have differential effects on intraspecific and interspecific variation, with three possible situations: effect at one level only, effect at both levels with the same polarity but potentially different intensity, and effects that oppose between levels. Whereas the impact of all selective agents is direct in macroevolution, microevolution requires intraspecific competition as a mediator between selective agents and evolutionary responses. This mediating role of intraspecific competition occurs in the presence of sexual reproduction and has therefore no analogue at the macroevolutionary level where species are the evolutionary units. Competition between species manifests both on the microevolutionary and macroevolutionary level, but with different effects. In microevolution, interspecific competition spurs evolutionary divergence, whereas it is a potential driver of extinction at the macroevolutionary level. Recasting the Red Queen hypothesis in a macroevolutionary framework suggests that the effects of interspecific competition result in a positive correlation between origination and extinction rates, confirming empirical observations herein referred to as Stanley's rule.     

Cephalisation bei Caniden

Cephalisation in Canidae Studied were the intraspecific and interspecific relationships between brain weight and body weight in Canidae. Inclination values of the allometric lines: intraspecific – 0,25, interspecific 0,571. Most of the studied species have nearly the same degree of cephalisation, deviations from the interspecific allometric line are small; the cephalisation of Nyctereutes and Otocyon is less developed than in the other canid species. There is no difference in cephalisation between most canids and felids. Mustelids show a high variability in cephalisation. Criticized were the data of Bauchot (1985) and Gittleman (1986) on brain weight and body weight.     

Complex competitive interactions in four species of Lucilia blowflies

Abstract.

• 1 The effects of intraspecific and interspecific larval competition on larval survival, adult size, adult longevity and fecundity were quantified in four species of coexisting Lucilia blowflies: illustris, silvarum, sericata and caesar.
• 2 There was a general negative effect of increasing density on larval and adult survival, size and fecundity. Additionally, complex species-specific and frequency-dependent responses were identified, which were not expected in these biologically and morphologically closely similar species.
• 3 Lucilia illustris, the numerically dominant species in the natural community, was a superior competitor to L.silvarum at intermediate densities but an inferior competitor at high density. Such nonlinear responses may be related to differences in the life histories and larval behaviour of the species (bigger eggs and more contest-type outcome of competition in L.silvarum).
• 4 We parameterized a model of interspecific competition on a subdivided resource in an attempt to reconcile the conflicting results on larval competitive abilities and the abundances of the species in the field. Using laboratory and field-estimated parameter values the model predicted coexistence of L.illustris and L.silvarum and the observed numerical dominance of the former species. The average densities of flies in the field are limited to relatively low levels, apparently preventing L.silvarum (the superior competitor at high density) from dominating and excluding L. illustris.

     

Differential effect of inter- and intraspecific competition on the performance of invasive and native Taraxacum species

Inter- and intraspecific competitive abilities are significant determinants of invasive success and the ecological impact of non-native plants. We tested two major hypotheses on the competitive ability of invasive species using invasive (Taraxacum officinale) and native (T. platycarpum) dandelions: differential interspecific competitive ability between invasive and native species and the kin recognition of invasive species. We collected seeds from two field sites where the two dandelion species occurred nearby. Plants were grown alone, with kin (plants from the same maternal genotype) or strangers (plants from different populations) of the same species, or with different species in a growth chamber, and the performance at the early developmental stage between species and treatments was compared. The invasive dandelions outcompeted the native dandelions when competing against each other, although no difference between species was detected without competition or with intraspecific competition. Populations of native species responded to interspecific competition differently. The effect of kinship on plant performance differed between the tested populations in both species. A population produced more biomass than the other populations when grown with a stranger, and this trend was manifested more in native species. Our results support the hypothesis that invasive plants have better competitive ability than native plants, which potentially contributes to the establishment and the range expansion of T. officinale in the introduced range. Although kin recognition is expected to evolve in invasive species, the competitive ability of populations rather than kinship seems to affect plant growth of invasive T. officinale under intraspecific competition.     

Effects of spatial aggregation on competition,complementarity and resource use

Abstract The spatial distributions of most species are aggregated to varying degrees. A limited number of studies have examined the effects of spatial aggregation on interspecific and intraspecific interactions, generally finding that spatial aggregation can enhance coexistence between species by reducing the capacity for interspecific competition. Less well studied are the effects of spatial aggregation on complementarity (i.e. differences in resource use strategies) and resource use. Our primary hypothesis was that spatial aggregation reduces the complementarity between species owing to: (i) less interspecific interactions as a result of spatial separation; and (ii) less differences between species as a result of phenotypic plasticity. We further postulate that these negative effects of spatial aggregation on complementarity will reduce resource use by the community. Here we test these hypotheses in a pot experiment in which we applied three levels of spatial aggregation to three sets of two‐species mixtures of herbaceous perennial plant species from native grasslands of south‐eastern Australia. Both root and shoot biomass were significantly affected by spatial aggregation, although the nature of these affects depended upon the species involved, and the relative strengths of interspecific versus intraspecific competition. Complementarity between species in the distribution of their green leaves decreased significantly as spatial aggregation increased for one of the species mixtures, providing some evidence in support of our hypothesis that aggregation reduces complementarity through phenotypic plasticity. Spatial aggregation also altered light interception and use of soil moisture resources, although these effects were dependent on the species involved. We suggest that clear effects of spatial aggregation on complementarity and resource use may be obscured by the idiosyncratic way in which neighbour identity influences plant growth and hence plant size, limiting the ability to generalize, at the community level, any underlying effects of spatial pattern on ecological process.     

The ecology of cooperative breeding behaviour

Ecology is a fundamental driving force for the evolutionary transition from solitary living to breeding cooperatively in groups. However, the fact that both benign and harsh, as well as stable and fluctuating, environments can favour the evolution of cooperative breeding behaviour constitutes a paradox of environmental quality and sociality. Here, we propose a new model – the dual benefits framework – for resolving this paradox. Our framework distinguishes between two categories of grouping benefits – resource defence benefits that derive from group‐defended critical resources and collective action benefits that result from social cooperation among group members – and uses insider–outsider conflict theory to simultaneously consider the interests of current group members (insiders) and potential joiners (outsiders) in determining optimal group size. We argue that the different grouping benefits realised from resource defence and collective action profoundly affect insider–outsider conflict resolution, resulting in predictable differences in the per capita productivity, stable group size, kin structure and stability of the social group. We also suggest that different types of environmental variation (spatial vs. temporal) select for societies that form because of the different grouping benefits, thus helping to resolve the paradox of why cooperative breeding evolves in such different types of environments.