Habitat selection,interspecific interactions and landscape composition

Summary I argue here that, from the perspective of any individual, most landscapes are composed of only three basic types of habitats. These are: (1) source habitat in which reproduction exceeds mortality and the expected per capita growth rate is greater than one; (2) sink habitat, in which limited, reproduction is possible but will not on average, compensate for mortality and the per capita rate of growth is between zero and one; and (3) unusable habitat, which comprises the matrix of all habitats that are never exploited by the species in question, and in which patches of source and sink habitats are embedded. Unlike earlier source-sink models, this model explicitly considers the effects that substituting one type of habitat for another has on the equilibrium size of a population and the interactions between species which can use both source and sink habitats. The model demonstrates that the equilibrium size of a species' population can sometimes be increased by substituting unusable habitat for sink habitat. Thus, even though the average patch quality in the landscape may be decreased, the overall quality of the landscape can increase. For two species with distinct habitat preferences, interactions between species can vary qualitatively as well as quantitatively as a function of the relative abundances of each of the habitat types. The model also shows that the interactions between species are particularly sensitive to the relative costs of moving between patches and sampling patches to determine their quality. Recent fragmentation of natural landscapes may increase the cost of searching for usable (source or sink) patches. Under some conditions, the interspecific interactions may be substantially more negative (competitive) than the interactions that evolved in the original natural landscape, further reducing population sizes and increasing the likelihood of competitive exclusion in fragmented modern landscapes.     

Chemical warfare or modulators of defence responses - the function of secondary metabolites in plant immunity

In plants, a host's responses to an attempted infection include activation of various secondary metabolite pathways, some of which are specific for particular plant phylogenetic clades. Phytochemicals that represent respective end products in plant immunity have been stereotypically linked to antimicrobial properties. However, in many cases, owing to the lack of unequivocal evidence for direct antibiotic action in planta, alternative functions of secondary metabolites should be considered. Correspondingly, recent findings have identified novel, and rather unexpected, functions of phytochemicals in plant immunity that mediate regulatory pathways for conserved defence responses. It also seems likely that these conserved responses can be regulated by clade-specific phytochemicals.     

Population regulation and role of mesozooplankton in shaping marine pelagic food webs

Copepods constitute the majority of the mesozooplankton in the oceans.By eating and being eaten copepods have implications for the flow of matterand energy in the pelagic environment. I first consider populationregulation mechanisms in copepods by briefly reviewing estimates of growthand mortality rates and evidence of predation and resource limitation. Theeffects of variations in fecundity and mortality rates for the demography ofcopepod populations are then examined by a simple model, which demonstratesthat population growth rates are much more sensitive to variations inmortality than to variations in fecundity. This is consistent with theobserved tremendous variation in copepod fecundity rates, relatively low andconstant mortality rates and with morphological and behavioralcharacteristics of pelagic copepods (e.g., predator perception and escapecapability, vertical migration), which can all be considered adaptations topredator avoidance. The prey populations of copepods, mainly protozoa(ciliates) and phytoplankton, may be influenced by copepod predation tovarying degrees. The highly variable morphology and the population dynamics(e.g., bloom formation) of the most important phytoplankton prey populations(diatoms, dinoflagellates) suggest that predation plays a secondary role incontrolling their dynamics; availability of light and nutrients as well ascoagulation and sedimentation appear generally to be more important. Thelimited morphological variation of planktonic ciliates, the well developedpredator perception and escape capability of some species, and the oftenresource-unlimited in situ growth rates of ciliates, on the other hand,suggest that copepod predation is important for the dynamics of theirpopulations. I finally examine the implications of mesozooplankton activityfor plankton food webs, particularly their role in retarding vertical fluxesand, thus, the loss of material from the euphotic zone. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chemical cues from multiple predator-prey interactions induce changes in behavior and growth of anuran larvae

Chemical signals are used as information by prey to assess predation risk in their environment. To evaluate the effects of multiple predators on prey growth, mediated by a change in prey activity, I exposed small and large bullfrog (Rana catesbeiana) larvae (tadpoles) to chemical cues from different combinations of bluegill sunfish (Lepomis macrochirus) and larval dragonfly (Anax junius) predators. Water was regularly transferred from predation trials (outdoor experiment) to aquaria (indoor experiment) in which activity and growth of tadpoles was measured. The highest predation mortality of small bullfrog larvae in the outdoor experiment was due to Anax, and it was slightly lower in the presence of both predators, probably resulting from interactions between predators. There was almost no mortality of prey with bluegill. The activity and growth of small bullfrog larvae was highest in the absence of predators and lowest in the presence of Anax. In the presence of bluegill only, or with both predators, the activity and growth of small bullfrog tadpoles was intermediate. Predators did not affect large tadpole activity and growth. Regressing mortality of small bullfrog tadpoles against activity and growth of bullfrog tadpoles revealed a significant effect for small bullfrog larvae but a non-significant effect for large bullfrog larvae. This shows that the response of bullfrog tadpoles to predators is related to their own body size. The experiment demonstrates that chemical cues are released both as predator odor and as alarm substances and both have the potential to strongly alter the activity and growth of prey. Different mechanisms by which chemical cues may be transmitted to species interactions in the food web are discussed. Received: 28 June 1999 / Accepted: 15 November 1999     

Human UDP-glucuronosyl transferases: Chemical defence,jaundice and gene therapy

Human UDP-glucuronosyltransferases (UDPGTs) are a family of enzymes which detoxify many hundreds of compounds by their conjugation to glucuronic acid, rendering them both harmless and more water soluble, hence, excretable. The level of expression of each UDPGT isoform in the body is the result of interplay between temporal, tissue-specific and environmental regulators. This complexity contributes to the difficulty in predicting the metabolic fate of compounds. Genetic defects and polymorphisms affecting individual isoform activities have deleterious and potentially lethal effects, as exemplified by the severe hyperbilirubinaemia observed in Crigler-Najjar Syndrome. Such severe genetic defects in bilirubin glucuronidation are obvious candidates for antenatal screening and gene therapy.     

The role of nutrition, crowding and interspecific interactions in the development of winged aphids

1. Winged morph production in aphids is a phenotypic trait that has traditionally been seen as a response to unfavourable environmental conditions. The evidence to support this theory is reviewed and the ecological and evolutionary significance of the findings is discussed. 2. The common assertion of poor host‐plant nutritional quality leading to increased production of winged morphs does not always apply, particularly when the host‐plant quality is exceptionally poor. The available data are skewed heavily towards Myzus persicae, and for this species the dynamical change in plant quality appears to be important with respect to wing induction. 3. Crowding may be a less influential stimulus for wing induction as study methods approach natural conditions experienced by aphids on their host plant. 4. The growing evidence that interactions with other organisms can induce the production of winged morphs by aphid colonies is reviewed. In the case of natural enemies, such a response by an aphid colony may be regarded as induced defence. Wing induction may also act as a means of transmission for a virus or fungal pathogen.     

63Environmental change, interspecific interactions, and shifting algal distributions on rocky shores

Because intertidal organisms live close to their environmental tolerances, intertidal species are considered early harbingers of the effects of global change. Using a combination of spatial environmental gradients and long-term datasets, I examine the likely consequences of global warming on the distribution of Mazzaella parksii (formerly Mazzaella cornucopiae ), a turf-forming red alga. On Tatoosh Island, WA, M. parksii is restricted almost entirely to north-facing surfaces. On south-facing slopes, the upper limit of M. parksii , which is set by abiotic stress, occurs much lower on the shore. However, its lower limit, which is set by herbivores, does not vary with aspect. Because its upper and lower limits are independent across the aspect gradient, M. parksii is effectively squeezed out of the system as one moves from a north-facing to a south-facing slope. This general pattern is observed at several spatial scales across gradients of wave exposure and air temperature. The vertical distributional patterns of M. parksii also shift across temporal gradients. Over the past 25 years, the upper limit of M. parksii on Tatoosh Island has shifted downshore by approximately 25 cm. Most of this change was driven by three consecutive harsh summers in the mid 1990's. These temporal patterns, combined with the insight gained from spatial patterns, suggest that M. parksii may go locally extinct in many parts of its range as its upper and lower limits converge. Furthermore, because vertical distributional shifts are linked to stochastic climatic effects, temporal change in marine algal populations may be rapid and unexpected.     

Intra and interspecific association of large pelagic fishes inferred from catch data of surface longline

Synopsis This paper analyses the distribution of longline catches of swordfish, Xiphias gladius, and six species of pelagic elasmobranchs, during a fishing voyage in the tropical eastern Atlantic. Seven scales of sampling units, ranging from about 0.72 to 7.2 km were used. Observed frequencies of appearance of each species in the basic sampling unit, were compared with theoretical frequencies obtained from the Poisson and negative binomial distributions. For the study of the interspecific relationships, contingency tables were used and the degree of association was estimated using the ²test and the coefficient v of Kendall. The catch distribution of the swordfish and the devil ray (Mobula sp.) can be explained by both randomness and a slight trend to association. For the pelagic sharks, a clear trend towards intraspecific clustering was found. Catches of two species of the genus Carcharhinus showed the most positive trends to interspecific association, especially in short ranges, probably due to attraction to previously hooked fish. The possible causes of these distributions are discussed.     

The shaping of social perception by stimulus and knowledge cues to human animacy

Although robots are becoming an ever-growing presence in society, we do not hold the same expectations for robots as we do for humans, nor do we treat them the same. As such, the ability to recognize cues to human animacy is fundamental for guiding social interactions. We review literature that demonstrates cortical networks associated with person perception, action observation and mentalizing are sensitive to human animacy information. In addition, we show that most prior research has explored stimulus properties of artificial agents (humanness of appearance or motion), with less investigation into knowledge cues (whether an agent is believed to have human or artificial origins). Therefore, currently little is known about the relationship between stimulus and knowledge cues to human animacy in terms of cognitive and brain mechanisms. Using fMRI, an elaborate belief manipulation, and human and robot avatars, we found that knowledge cues to human animacy modulate engagement of person perception and mentalizing networks, while stimulus cues to human animacy had less impact on social brain networks. These findings demonstrate that self–other similarities are not only grounded in physical features but are also shaped by prior knowledge. More broadly, as artificial agents fulfil increasingly social roles, a challenge for roboticists will be to manage the impact of pre-conceived beliefs while optimizing human-like design.     

Chemical defence in chrysomelid eggs and neonate larvae

ABSTRACT. Eggs and neonate larvae of chrysomelid beetles (sub-tribes Chrysomelina and Phyllodectina) were investigated for the presence of defensive substances.
The two isoxazolinone glucosides (compounds 1 and 2), characteristic of the adult defence secretion, were detected in the eggs of all studied species. Compound 2, containing a nitropropionate, is always present in concentrations (above 10^-2 M), which are highly deterrent to the ant Myrmica rubra. This compound is not at all or only slightly toxic to ants at 10^-2 M. Compound 1, devoid of nitropropionate, is a minor constituent, and is neither deterrent nor toxic to ants.
The five Chrysomela species studied and Phratora vitellinae also sequester salicin in their eggs in amounts highly deterrent and toxic to ants. A single Chrysomela egg often contains enough salicin to kill an ant. While the isoxazolinones are discarded with the egg shells, salicin is used by neonate larvae as a precursor for the production of salicylaldehyde in the thoracic defence glands, already functional at hatching. No salicin could be detected in the eggs of those species whose larvae produce cyclopentanoid monoterpenes, even if they feed on Salicaceae. No larva of any species seems to be able to produce detectable amounts of monoterpenes at birth. A very early defence, possible only in those species using salicin as the precursor for their defensive secretion, could be highly advantageous in protecting the clustered larvae during the long process of hatching and in avoiding cannibalism between siblings.
Only trace amounts of oleic acid were found in the eggs of Gastrophysa viridula , in contrast to previous reports on its presence in large quantities in the American G. cyanea.     

Host-microbe interactions: shaping the evolution of the plant immune response

The evolution of the plant immune response has culminated in a highly effective defense system that is able to resist potential attack by microbial pathogens. The primary immune response is referred to as PAMP-triggered immunity (PTI) and has evolved to recognize common features of microbial pathogens. In the coevolution of host-microbe interactions, pathogens acquired the ability to deliver effector proteins to the plant cell to suppress PTI, allowing pathogen growth and disease. In response to the delivery of pathogen effector proteins, plants acquired surveillance proteins (R proteins) to either directly or indirectly monitor the presence of the pathogen effector proteins. In this review, taking an evolutionary perspective, we highlight important discoveries over the last decade about the plant immune response.     

Resource partitioning and interspecific interactions among sympatric rain forest arboreal mammals of the Western Ghats, India

Resource partitioning in a community of diurnal arboreal mammalsconsisting of the lion-tailed macaque Macaca silenus, bonnetmacaque (BM) Macaca radiata, Nilgiri langur Semnopithecus johnii,and the Indian giant squirrel Ratufa indica of the Western Ghats,southern India, was studied. Differences in their diet, verticalstratification, food resource niche breadth, niche overlap,and behavioral interactions were examined. Resource partitioningwas through differential habitat use, resource use, and verticalstratification. Of the four species, the BM was not a residentspecies and made frequent forays into evergreen forest fromthe adjacent deciduous forest during the flowering season ofCullenia exarillata and fruiting season of Ficus microcarpa.The macaques had narrower niches, and the langur and the squirrelhad wider niches. Niche overlap was highest between the twomacaques. Overlap among the study species was particularly pronouncedduring the flowering of C. exarillata. There was significantcorrelation between niche overlap and intolerance among thestudy species. Certain species pairs showed little or no mutualintolerance despite high overlap. Cooperative interactions suchas alarm calls occurred more frequently among the resident species.Interaction matrices revealed an underlying pattern of interspecificdominance hierarchy, with the BM dominating over the other threespecies. Our study suggests that the BM do not coexist withthe other three because of high overlap with its congener andlow occurrence of cooperative interactions.     

Diversity in interspecific interactions between a nest-associating species, Pungtungia herzi, and multiple host species

Nest association in fishes affects the reproductive success of the host to varying degrees, from complete failure of the host’s reproduction to fitness advantages. Such varying impacts of nest association are considered to result from both the associate’s behavior and the characteristics of the host’s reproduction. To investigate the relationship between the impact of nest associate and host/associate ecology as well as evolutionary strategies involving nest association, we compared reproductive strategies and success between an associate East Asian minnow, Pungtungia herzi, and two host fishes (a goby, Odontobutis obscura, and a catfish, Pseudobagrus nudiceps) that have different reproductive ecologies. The associate frequently spawned around the days on which both hosts spawned, and gained a fitness advantage through continuous egg protection. Spawning by the associate had a negative effect on the survival of O. obscura eggs. Male O. obscura tended to abandon their nest when it was parasitized during the pre-spawning period. This is likely a tactic to alleviate the costs of brood parasitism. In contrast, survival of P. nudiceps eggs was consistently high in all nests, regardless of the intensity of associate’s spawning, and P. nudiceps young fed on cyprinid offspring (most probably the associate’s eggs/young) in the nest. Both P. nudiceps and P. herzi populations likely gain fitness benefits from their relationship. When comparing these two hosts with another known host, the freshwater perch Coreoperca kawamebari, the observed differences in the impact of nest association to the associate species likely correspond to differences in the spatial reproductive resources used by the respective hosts.     

Model analysis of the effect of environmental fluctuation on the species replacement pattern of pelagic fishes under interspecific competition

There are two factors affecting long-term fluctuation of planktotrophic pelagic fish: environmental fluctuation and interspecific competition. Long-term catch data of planktotrophic pelagic fishes in Japan suggest that the chub mackerel (species B) was replaced by the sardine (A), A was replaced by the anchovy, Pacific saury and horse mackerel (Group C), and species in group C were replaced by species B. If species A defeats B, B defeats C, and C defeats A in interspecific competitive ability, then the abundance of these three groups fluctuate forever and dominate in the same order. We call this cyclic advantage hypothesis for species replacement. In this model, environmental fluctuation affects the species replacement as a trigger. Environmental fluctuation does not determine the next dominant species but greatly affects when the next replacement occurs.     

Intra- and interspecific cohabitation of scorpions in the field and the effect of density, food, and shelter on their interactions

Scorpion cohabitation was studied qualitatively and quantitatively for several years in the field and in controlled experimental conditions in the laboratory. In the field, several cases were recorded of scorpions sharing the same shelter, either intra- or interspecifically. Intraspecific cohabitation was more prevalent than interspecific cohabitation. Among the five scorpion species studied here, Compsobuthus werneri judaicus shows the highest degree of sociality and aggregates both intra- and interspecifically. Leiurus quinquestriatus was never observed to cohabit interspecifically. Both Buthotus judaicus and C. werneri judaicus shared shelters with other scorpions more frequently during the wet season, whereas Nebo hierichonticus and Scorpio maurus fuscus cohabitated more often during the dry season. Under controlled laboratory conditions, density and availability of either food or shelter appear to be significant in facilitating cohabitation, even in the more aggressive species. Received: April 28, 1999 / Accepted: July 30, 1999     

The role of mating preferences in shaping interspecific divergence in mating signals in vertebrates

Vertebrates represent one of the best-studied groups in terms of the role that mating preferences have played in the evolution of exaggerated secondary sexual characters and mating behaviours within species. Vertebrate species however, also exhibit enormous interspecific diversity in features of mating signals that has potentially led to reproductive isolation and speciation in many groups. The role that sexual selection has played in interspecific divergence in mating signals has been less fully explored. This review summarizes our current knowledge of how mating preferences within species have shaped interspecific divergence in mate recognition signals among the major vertebrate groups. Certain signal modalities appear to characterize mating signal diversification among different vertebrate taxa. Acoustic signals play an important role in mating decisions in anuran amphibians and birds. Here, different properties of the signal may convey information regarding individual, neighbor and species recognition. Mating preferences for particular features of the acoustic signal have led to interspecific divergence in calls and songs. Divergence in morphological traits such as colouration or ornamentation appears to be important in interspecific diversity in certain groups of fishes and birds. Pheromonal signals serve as the primary basis for species-specific mating cues in many salamander species, most mammals and even some fishes. The evolution of interspecific divergence in elaborate courtship displays may have played an important role in speciation of lizards, and particular groups of fishes, salamanders, birds and mammals. While much research has focused on the importance of mating preferences in shaping the evolution of these types of mating signals within species, the link between intraspecific preferences and interspecific divergence and speciation remains to be more fully tested. Future studies should focus on identifying how variation in mating preferences within a species shapes interspecific diversity in features of mating signals in order to better understand how sexual selection may have led to speciation in vertebrates.