Does juvenile competition explain displacement of a native crayfish by an introduced crayfish?

The coldwater crayfish Orconectes eupunctus is endemic to the Spring and Eleven Point Rivers of Arkansas and Missouri, and appears to have been displaced from a portion of its range by the recently introduced ringed crayfish Orconectes neglectus. We examined competition among juveniles as a potential mechanism for this crayfish species displacement through laboratory and field experiments. Orconectes eupunctus juveniles survived and grew in stream cages in their former range, implicating biotic interactions rather than habitat degradation in the displacement. Laboratory experiments revealed O. neglectus juveniles were dominant in the presence of limited food, whereas size rather than species determined occupancy of limited shelter. In a field competition experiment using stream cages, O. neglectus juveniles did not inhibit growth or reduce survival of O. eupunctus juveniles. Consequently, laboratory evidence of O. neglectus dominance did not correspond with competition under field conditions. Combined with previous studies examining the effects of O. neglectus on O. eupunctus, these results suggest that competition may not be a factor in this crayfish species displacement. Alternate mechanisms for the apparent displacement of O. eupunctus by O. neglectus, such as differential predation or reproductive interference, should be investigated.     

Does a top predator reduce the predatory impact of an invasive mesopredator on an endangered rodent?

The mesopredator release hypothesis (MRH) predicts that reduced abundance of top‐order predators results in an increase in the abundance of smaller predators (mesopredators) due to a reduction in intra‐guild predation and competition. The irruption of mesopredators that follows the removal of top‐order predators can have detrimental impacts on the prey of the mesopredators. Here we investigated the mechanisms via which the presence of a top‐order predator can benefit prey species. We tested predictions made according to the MRH and foraging theory by contrasting the abundances of an invasive mesopredator (red fox Vulpes vulpes) and an endangered prey species (dusky hopping mouse Notomys fuscus), predator diets, and N. fuscus foraging behaviour in the presence and absence of a top‐predator (dingo Canis lupus dingo). As predicted by the MRH, foxes were more abundant where dingoes were absent. Dietary overlap between sympatric dingoes and foxes was extensive, and fox was recorded in 1 dingo scat possibly indicating intra‐guild predation. Notomys fuscus were more likely to occur in fox scats than dingo scats and as predicted by the MRH N. fuscus were less abundant in the absence of dingoes. The population increase of N. fuscus following rainfall was dampened in the absence of dingoes suggesting that mesopredator release can attenuate bottom‐up effects, although it remains conceivable that differences in grazing regimes associated with dingo exclusion could have also influenced N. fuscus abundance. Notomys fuscus exhibited lower giving‐up densities in the presence of dingoes, consistent with the prediction that their perceived risk of predation would be lower and foraging efficiency greater in the presence of a top‐predator. Our results suggest that mesopredator suppression by a top predator can create a safer environment for prey species where the frequency of fatal encounters between predators and prey is reduced and the non‐consumptive effects of predators are lower.     

Does a top-predator provide an endangered rodent with refuge from an invasive mesopredator?

In arid environments, ecological refuges are often conceptualised as places where animal species can persist through drought owing to the localised persistence of moisture and nutrients. The mesopredator release hypothesis (MRH) predicts that reduced abundance of top-order predators results in an increase in the abundance of smaller predators (mesopredators) and consequently has detrimental impacts on the prey of the smaller predators. Thus according to the MRH, the existence of larger predators may provide prey with refuge from predation. In this study, we investigated how the abundance of an endangered rodent Notomys fuscus is affected by Australia's largest predator, the dingo Canis lupus dingo , introduced mesopredators, introduced herbivores, kangaroos and rainfall. Our surveys showed that N. fuscus was more abundant where dingoes occurred. Generalised linear modelling showed that N. fuscus abundance was associated positively with dingo activity and long-term annual rainfall and negatively with red fox Vulpes vulpes activity. Our results were consistent with the hypothesis that areas with higher rainfall and dingoes provide N. fuscus with refuge from drought and predation by invasive red foxes, respectively. Top-order predators, such as dingoes, could have an important functional role in broad-scale biodiversity conservation programmes by reducing the impacts of mesopredators.     

Does past evolutionary history under different mating regimes influence the demographic dynamics of interspecific competition?

Interspecific interactions are contingent upon organism phenotypes, and thus phenotypic evolution can modify interspecific interactions and affect ecological dynamics. Recent studies have suggested that male–male competition within a species selects for capability to reproductively interfere with a closely related species. Here, we examine the effect of past evolutionary history under different mating regimes on the demographic dynamics of interspecific competition in Callosobruchus seed beetles. We used previously established experimental evolution lines of Callosobruchus chinensis that evolved under either forced lifelong monogamy or polygamy for 17 generations, and examined the demographic dynamics of competition between these C. chinensis lines and a congener, Callosobruchus maculatus. Callosobruchus chinensis was competitively excluded by C. maculatus in all trials. Time series data analyses suggested that reproductive interference from C. chinensis was relatively more important in the trials involving polygamous C. chinensis than those involving monogamous C. chinensis, in accordance with the potentially higher reproductive interference capability of polygamous C. chinensis. However, the estimated signs and magnitudes of interspecific interactions were not fully consistent with this explanation, implying the evolution of not only reproductive interference but also other interaction mechanisms. Our study thus suggests multifaceted effects of sexually selected traits on interspecific competitive dynamics.     

Does interspecific competition drive patterns of habitat use in desert bat communities?

Bodies of water are a key foraging habitat for insectivorous bats. Since water is a scarce and limiting resource in arid environments, bodies of open water may have a structuring effect on desert bat communities, resulting in temporal or spatial partitioning of bat activity. Using acoustic monitoring, we studied the spatial and temporal activity patterns of insectivorous bats over desert ponds, and hypothesised that sympatric bat species partition the foraging space above ponds based on interspecific competitive interactions. We used indirect measures of competition (niche overlap and competition coefficients from the regression method) and tested for differences in pond habitat selection and peak activity time over ponds. We examined the effect of changes in the activity of bat species on their potential competitors. We found that interspecific competition affects bat community structure and activity patterns. Competing species partitioned their use of ponds spatially, whereby each species was associated with different pond size and hydroperiod (the number of months a pond holds water) categories, as well as temporally, whereby their activity peaked at different hours of the night. The drying out of temporary ponds increased temporal partitioning over permanent ponds. Differences in the activity of species over ponds in response to the presence or absence of their competitors lend further support to the role of interspecific competition in structuring desert bat communities. We suggest that habitat use and night activity pattern of insectivorous bats in arid environments reflect the trade-offs between selection of preferred pond type or activity time and constraints posed by competitive interactions.     

Does interference competition with wolves limit the distribution and abundance of coyotes?

Interference competition with wolves Canis lupus is hypothesized to limit the distribution and abundance of coyotes Canis latrans, and the extirpation of wolves is often invoked to explain the expansion in coyote range throughout much of North America. We used spatial, seasonal and temporal heterogeneity in wolf distribution and abundance to test the hypothesis that interference competition with wolves limits the distribution and abundance of coyotes. From August 2001 to August 2004, we gathered data on cause-specific mortality and survival rates of coyotes captured at wolf-free and wolf-abundant sites in Grand Teton National Park (GTNP), Wyoming, USA, to determine whether mortality due to wolves is sufficient to reduce coyote densities. We examined whether spatial segregation limits the local distribution of coyotes by evaluating home-range overlap between resident coyotes and wolves, and by contrasting dispersal rates of transient coyotes captured in wolf-free and wolf-abundant areas. Finally, we analysed data on population densities of both species at three study areas across the Greater Yellowstone Ecosystem (GYE) to determine whether an inverse relationship exists between coyote and wolf densities. Although coyotes were the numerically dominant predator, across the GYE, densities varied spatially and temporally in accordance with wolf abundance. Mean coyote densities were 33% lower at wolf-abundant sites in GTNP, and densities declined 39% in Yellowstone National Park following wolf reintroduction. A strong negative relationship between coyote and wolf densities (beta = -3.988, P < 0.005, r(2) = 0.54, n = 16), both within and across study sites, supports the hypothesis that competition with wolves limits coyote populations. Overall mortality of coyotes resulting from wolf predation was low, but wolves were responsible for 56% of transient coyote deaths (n = 5). In addition, dispersal rates of transient coyotes captured at wolf-abundant sites were 117% higher than for transients captured in wolf-free areas. Our results support the hypothesis that coyote abundance is limited by competition with wolves, and suggest that differential effects on survival and dispersal rates of transient coyotes are important mechanisms by which wolves reduce coyote densities.     

Does pollen competition reduce the cost of inbreeding?

We hypothesize that floral features promoting pollen competition in angiosperms may have evolved, in some cases, in response to selection generated by the negative effects of inbreeding, at least in plants with mixed-mating systems. Screening of haploid genotypes through pollen competition may purge recessive (or additive) deleterious alleles that are expressed in haploid pollen and hence may reduce the fitness cost of self-pollination, geitonogamy, or biparental inbreeding. We tested one prediction of this hypothesis, that offspring produced by more intense competition among self-pollen have higher fitness than offspring produced by less intense competition. Dalechampia scandens (Euphorbiaceae) flowers were pollinated with pollen from other flowers on the same plant (geitonogamous self-fertilization). Those flowers experiencing more intense pollen competition as a result of low pollen dispersion (positional variance) on the stigma produced heavier seeds and seedlings with faster-growing radicles than flowers experiencing less intense pollen competition (high pollen dispersion), as predicted by our hypothesis.     

Does kin structure explain the occurrence of workers in a lower termite?

Kinship plays a fundamental role in the origin of social life. It is also predicted to affect numerous details within animal societies, yet recent studies revealed equivocal results. We tested the influence of relatedness for the occurrence of workers in the termite Cryptotermes secundus. Here individuals are developmentally flexible to remain workers or to become dispersing sexuals that found new colonies. Furthermore, colony relatedness naturally increases with inbreeding and decreases when neighboring colonies fuse. Similar to recent studies on social Hymenoptera, our experimental change in relatedness gave equivocal results. Reducing relatedness within colonies did not have an effect, but individuals in inbred colonies were less likely to disperse and more likely to remain workers as predicted by kinship arguments. Several explanations for the interpretation of these equivocal results are provided.     

All the eggs in one basket: Are island refuges securing an endangered passerine?

Refuges for threatened species are important to prevent species extinction. They provide protection from a range of environmental and biotic stressors, and ideally provide protection against all threatening processes. However, for some species it may not be clear why some areas are refuges and others are not. The forty‐spotted pardalote (Pardalotus quadragintus) is an endangered, sedentary, cryptic and specialised bird endemic to the island of Tasmania, Australia. Having undergone an extreme range contraction over the past century the species is now mostly confined to a few small offshore island refuges. Key threatening processes to the species include habitat loss, wildfire, competition and predation. The ways in which these processes have molded the species’ contemporary range have not been clearly evaluated. Furthermore, the security of the remnant population within refuges is uncertain. To overcome this uncertainty we assessed key threats and established the population status in known refuges by developing a robust survey protocol within an occupancy modelling framework. We discuss our results in the context of planning trial reintroductions of this endangered species in suitable habitat across its former range. We found very high occupancy rates (0.75–0.96) at two refuges and in suitable conditions, the species was highly detectable (p, 0.43–0.77). At a third location our surveys indicated a local extinction, likely due to recent wildfire. We demonstrate that all refuges are at high risk of one or more threatening processes and the current distribution across island refuges is unlikely to secure the species from extinction. We identified large areas of potential habitat across the species’ former mainland range, but these are likely too distant from source populations for natural recolonisation. We propose that establishing new populations of forty‐spotted pardalotes via reintroduction is essential to secure the species and that this is best achieved while robust source populations still exist.     

Antipodean white sharks on a Mediterranean walkabout? Historical dispersal leads to genetic discontinuity and an endangered anomalous population

The provenance of white sharks (Carcharodon carcharias) in the Mediterranean is both a conundrum and an important conservation issue. Considering this species's propensity for natal philopatry, any evidence that the Mediterranean stock has little or no contemporary immigration from the Atlantic would suggest that it is extraordinarily vulnerable. To address this issue we sequenced the mitochondrial control region of four rare Mediterranean white sharks. Unexpectedly, the juvenile sequences were identical although collected at different locations and times, showing little genetic differentiation from Indo-Pacific lineages, but strong separation from geographically closer Atlantic/western Indian Ocean haplotypes. Historical long-distance dispersal (probably a consequence of navigational error during past climatic oscillations) and potential founder effects are invoked to explain the anomalous relationships of this isolated 'sink' population, highlighting the present vulnerability of its nursery grounds.     

Does the inhibition of microvillus protein phosphorylation by lysine explain the activity of the latter on calcium transfer?

• 1.1. Is the activity of l-lysine on calcium absorption related to the fact that its phosphorylation is competitive with that of the microvilli proteins involved in the mineral transfer?
• 2.2. The microvilli proteins phosphorylation is not cyclic GMP-dependent but is actually inhibited by l-lysine, used in general at a 100 mM concentration.
• 3.3. The electrophoresis is followed by an autoradiograph which reveals the existence of a phosphorylated protein with a molecular weight of 140,000 daltons. Another phosphorylable protein, clearly visible in some preparations but only detectable in others, has a molecular weight close to 70,000 daltons.
• 4.4. The inhibition by lysine of the microvilli proteins phosphorylation is not specific to a given protein, but is also observed for phosphorylable cytosolic proteins.
• 5.5. A scheme for calcium transfer is proposed. It involves a protein whose phosphorylation should reduce the membrane permeability to calcium.
• 6.6. The following three attributes of the phosphorylable membrane protein—its molecular weight; the fact that another protein (probably its monomer) is also phosphorylable; its well known capacity for phosphorylation—suggest that this protein might actually be alkaline phosphatase whose correlations in calcium metabolism are well known.

     

Gene flow between an endangered endemic iguana, and its wide spread relative, on the island of Utila, Honduras: when is hybridization a threat?

The island endemic Ctenosaura bakeri was listed as critically endangered by the IUCN Redlist Assessment in 2004, 7 years after it was recognized as a distinct species. C. bakeri occupies a portion of Utila, a small continental island located off the northern coast of Honduras. Habitat destruction and over-harvesting are among the top threats facing this species. In addition, morphological evidence of hybridization was recently documented, raising the concern that gene flow from the common and widely distributed C. similis could threaten the genetic distinctiveness of C. bakeri. We show that hybridization occurs only at low levels and is not a current threat to C. bakeri. All ctenosaurs captured for this study were identified to species level without difficulty; none had intermediate or mosaic phenotypes. Sequence analysis of mitochondrial and nuclear markers revealed only two individuals with introgressed genotypes. Molecular analysis of the previously described hybrid showed it to be heterozygous for C. bakeri and C. similis alleles. Hybridization between these two species is possible and occurs occasionally in the wild, and the rate of hybridization could increase if habitat destruction or changes in relative abundance increase the probability of interbreeding. However, the level of gene flow indicated by current data is too low to threaten C. bakeri with genetic swamping or deleterious fitness effects.     

Does competition drive character differences between species on a macroevolutionary scale?

Sympatric sister species generally have a degree of phenotypic differentiation that allows them to coexist. It has been well documented that phenotypic similarity results, through resource competition, in one of two major outcomes: local extinction of either competitor or character displacement. Limiting similarity suggests that there is a maximum degree of phenotypic niche overlap with which similar species may coexist. Breaching that maximum would result in exclusion. Character displacement, on the other hand, implies that the species differentiate phenotypically so that resource competition is reduced to the point where coexistence is possible. While it has been suggested that these theories have the potential to accelerate (character displacement) or limit phenotypic evolution (competitive exclusion) on microevolutionary time scales, their effects on macroevolution remain under‐studied. If competition accelerates evolution on a macroevolutionary scale, one would expect that phenotypic diversity increases as novel species ‘push aside’ existing species. On the other hand, one might also expect that phenotypic evolution comes to a halt as novel species are trapped in the (ever decreasing) phenotypic space not yet occupied by existing species, except at the extremes of the phenotypic spectrum. Studying the current geographical ranges of more than 3000 extant species representing 29 mammalian families and their respective body masses, I found little evidence of competition accelerating body size differentiation between species.     

Sleeping with the ‘enemy’: hybridization of an endangered tree weta

While hybridization is an important part of the evolutionary process, for rare species mating with more common species hybridization can increase the risks of extinction. By mating with heterospecifics rare species waste valuable reproductive resources and as a result population sizes may decline. If introgression occurs, the rare species can become genetically swamped by alleles from the more common species, rendering it effectively extinct. As a consequence of these risks, hybridization with the more common species Hemideina femorata (Canterbury tree weta) may lead to the extinction of the range restricted species H. ricta (Banks Peninsula tree weta) on Banks Peninsula. The current study uses spatial interpolation to model the distribution of each species and the potential sympatric zone to guide sampling efforts. Polymorphic microsatellite markers and mitochondrial sequence data were used to determine the extent of hybridization between H. ricta and H. femorata. The results confirm that hybridization is possible between these species. However, hybrids and introgression appear to be very rare, suggesting that reproductive isolating barriers are present but incomplete. The threat of extinction to H. ricta via hybridization with H. femorata is low but extreme loss of habitat may cause changes to population densities that could increase the risks of hybridization. Therefore, landowners should be encouraged to conserve native bush.