Larger Congener Research Articles

Response of forest Turtur doves to conspecific and congeneric songs in sympatry and allopatry

Birds have a diverse acoustic communication system, and the ability to recognise their own species’ song from a distance facilitates complex behaviours related to mate attraction and rival deterrence. However, certain species, including doves, do not learn songs and their vocal repertoires are much simpler than those of better-studied songbirds. In these so-called non-learning birds, relatively little is known about the role that bird song plays in intra- and interspecific interactions, and how such behaviours might be acquired (inherited or learned from experience). To investigate this question, we focused on two species of African wood doves whose long-range songs are used in a territorial context. Specifically, we examined the responses of sympatric and allopatric populations of male blue-headed wood-doves (Turtur brehmeri) and tambourine doves (Turtur tympanistria) to different types of simulated territorial intrusions, i.e. playback of conspecific, congeneric, and control songs. We aimed to assess (i) whether these species, which have similar songs, respond only to their own species' song or exhibit interspecific territoriality, and (ii) if the response pattern is affected by the presence or absence of congeners in the general area. We found that both species responded strongly to playback of their own species in both sympatric and allopatric populations. In allopatry, though, male tambourine doves misdirected their response and also approached the playback of congeneric songs. Our results indicate that, in areas where the studied Turtur doves live in sympatry, they do not exhibit consistent interspecific territoriality. However, we cannot exclude the possibility that the smaller tambourine dove avoids its larger congener during the process of territory establishment. The difference in tambourine doves’ response toward the song of present (sympatric) or absent (allopatric) congeners suggests that the ability to discriminate between songs of similarly singing potential competitors is acquired through earlier interactions and learning. This plasticity in response supports the misdirected aggression hypothesis, which argues that interspecific territorialism emerges as a maladaptive by-product of signal similarity. However, on an evolutionary timescale, such an ability could be considered an adaptive cognitive tool useful for resolving competing interests with congeners.

How far westward? Revisiting the distribution of Arctonyx badgers in the westernmost global range

Abstract Bangladesh delimits the westernmost range of Arctonyx badgers, but their presence in the country is not completely understood. The whole of Bangladesh is reportedly home to the northern hog badger (A. albogularis); however, there is no valid record to date. The greater hog badger (Arctonyx collaris), its larger congener and a globally vulnerable mustelid, has three valid records. This work, between 2001 and 2021, traced 28 records (all of A. collaris: 20 from literature review and social media, 8 from camera-trapping) in Bangladesh including four rare cases of erythrism and seven conflict incidents. All but five were from mixed evergreen forests of southeast Bangladesh, the known A. collaris range. One record was from wet deciduous forests of northern Bangladesh (bordering Meghalaya, India), a region not previously marked as an A. collaris range. In 2021, from 4436 trap-nights of sampling, 17 notionally-independent events (all night-time) were obtained. This produced the first evidence of A. collaris in northeast Bangladesh, a region that borders the Tripura Hills, India (where it was first recorded in 2020) and belongs to the Indo-Burma biodiversity hotspot. The work proves the existence of relict populations whereas the absence of A. albogularis signifies a re-assessment of its westernmost distribution.

The First Quaternary Record of the Rodent Akodon kadiweu Brandão, Percequillo, D'Elía, Paresque, & Carmignotto, 2021 (Rodentia: Cricetidae: Sigmodontinae).

Rodents of the genus Akodon comprise 41 extant species, and are considered the most diverse genus of the tribe Akodontini. The most recently described extant species is Akodon kadiweu, known exclusively from Serra da Bodoquena, a karstic region located in Mato Grosso do Sul state, Brazil. Some sub-fossil and fossil specimens of Akodon have been reported in recent years for Brazil, but most remain unidentified at the species level. Here we examine the identity of Quaternary specimens of Akodon sp. from the limestone cave Nossa Senhora Aparecida, located in Serra da Bodoquena. Quantitative characters allowed the distinction of Akodon sp. specimens from smaller and larger congeners, and skull qualitative characters of nasal, interorbital region, supraorbital margins, zygomatic notches, zygomatic plate, incisive foramina, mesopterygoid fossa, mandible and molars allowed to identify these individuals as A. kadiweu. Our results revealed the first known past representatives of Akodon to be recorded in Mato Grosso do Sul, as well as western Brazil.

Behavioural and energetic consequences of competition among three overwintering swan (Cygnus spp.) species

BackgroundWinter numbers of the northwest European population of Bewick’s Swans (Cygnus columbianus bewickii) declined recently by c. 40%. During the same period, numbers of two sympatric and ecologically-similar congeners, the Mute Swan (Cygnus olor) and Whooper Swan (Cygnus cygnus) showed increases or stability. It has been suggested that these opposing population trends could have a causal relationship, as Mute and Whooper Swans are larger and competitively dominant to Bewick’s Swans in foraging situations. If so, effects of competition of Mute and Whooper Swans on Bewick’s Swans should be detectable as measurable impacts on behaviour and energetics.MethodsHere, we studied the diurnal behaviour and energetics of 1083 focal adults and first-winter juveniles (“cygnets”) of the three swan species on their winter grounds in eastern England. We analysed video recordings to derive time-activity budgets and these, together with estimates of energy gain and expenditure, were analysed to determine whether individual Bewick’s Swans altered the time spent on key behaviours when sharing feeding habitat with other swan species, and any consequences for their energy expenditure and net energy gain.ResultsAll three swan species spent a small proportion of their total time (0.011) on aggressive interactions, and these were predominantly intraspecific (≥ 0.714). Mixed-effects models indicated that sharing feeding habitat with higher densities of Mute and Whooper Swans increased the likelihood of engaging in aggression for cygnet Bewick’s Swans, but not for adults. Higher levels of interspecific competition decreased the time spent by Bewick’s Swan cygnets on foraging, whilst adults showed the opposite pattern. When among low densities of conspecifics (< c. 200 individuals/km2), individual Bewick’s Swans spent more time on vigilance in the presence of higher densities of Mute and Whooper Swans, whilst individuals within higher density Bewick’s Swan flocks showed the opposite pattern. Crucially, we found no evidence that greater numbers of interspecific competitors affected the net energy gain of either adult or cygnet Bewick’s Swans.ConclusionsWe found no evidence that Bewick’s Swan net energy gain was affected by sharing agricultural feeding habitat with larger congeners during winter. This was despite some impacts on the aggression, foraging and vigilance behaviours of Bewick’s Swans, especially among cygnets. It is unlikely therefore that competition between Bewick’s Swans and either Mute or Whooper Swans at arable sites in winter has contributed to the observed decline in Bewick’s Swan numbers. Further research is needed, however, to test for competition in other parts of the flyway, including migratory stopover sites and breeding areas.

Winter Carnivory and Diapause Counteract the Reliance on Ice Algae by Barents Sea Zooplankton

The Barents Sea is a hotspot for environmental change due to its rapid warming, and information on dietary preferences of zooplankton is crucial to better understand the impacts of these changes on food-web dynamics. We combined lipid-based trophic marker approaches, namely analysis of fatty acids (FAs), highly branched isoprenoids (HBIs) and sterols, to compare late summer (August) and early winter (November/December) feeding of key Barents Sea zooplankters; the copepods Calanus glacialis, C. hyperboreus and C. finmarchicus and the amphipods Themisto libellula and T. abyssorum. Based on FAs, copepods showed a stronger reliance on a diatom-based diet. Phytosterols, produced mainly by diatoms, declined from summer to winter in C. glacialis and C. hyperboreus, indicating the strong direct linkage of their feeding to primary production. By contrast, C. finmarchicus showed evidence of year-round feeding, indicated by the higher winter carnivory FA ratios of 18:1(n-9)/18:1(n-7) than its larger congeners. This, plus differences in seasonal lipid dynamics, suggests varied overwintering strategies among the copepods; namely diapause in C. glacialis and C. hyperboreus and continued feeding activity in C. finmarchicus. Based on the absence of sea ice algae-associated HBIs (IP25 and IPSO25) in the three copepod species during both seasons, their carbon sources were likely primarily of pelagic origin. In both amphipods, increased FA carnivory ratios during winter indicated that they relied strongly on heterotrophic prey during the polar night. Both amphipod species contained sea ice algae-derived HBIs, present in broadly similar concentrations between species and seasons. Our results indicate that sea ice-derived carbon forms a supplementary food rather than a crucial dietary component for these two amphipod species in summer and winter, with carnivory potentially providing them with a degree of resilience to the rapid decline in Barents Sea (winter) sea-ice extent and thickness. The weak trophic link of both zooplankton taxa to sea ice-derived carbon in our study likely reflects the low abundance and quality of ice-associated carbon during late summer and the inaccessibility of algae trapped inside the ice during winter.

Why is the Northern Idaho Ground Squirrel Rare?

Urocitellus brunneus (northern Idaho ground squirrel) has a geographic range of approximately 1,600 km2 in west-central Idaho. It was listed as Threatened under the US Endangered Species Act in 2000. To assist recovery efforts, we tested three hypotheses that might explain its rarity: 1) specialization on a now uncommon habitat; 2) competition with a larger congener, U. columbianus (Columbian ground squirrel); and 3) anthropogenic impacts. We explored the habitat specialization hypothesis by comparing attributes of sites occupied exclusively by each species with areas occupied alternately by each. Sites occupied by U. brunneus had significantly more bare ground; shallower, rockier, harder soils; higher soil temperatures during the active season; less plant cover; shorter vegetation; lower net annual aboveground productivity; and fewer shrubs than sites occupied by U. columbianus. Discriminant analysis showed U. brunneus could occupy some areas used by U. columbianus, but U. columbianus seldom occupied areas occupied by U. brunneus. U. brunneus also occurred in earlier successional communities and could occupy mesic meadows with high water tables not utilized by U. columbianus. In field observations and arena trials, U. brunneus avoided U. columbianus. In two removal experiments U. brunneus expanded into areas from which U. columbianus had been removed, but vacated when U. columbianus returned. Anthropogenic impacts included habitat conversion, conifer invasion of meadows resulting from timber management and fire suppression practices, systematic poisoning, target shooting, and invasive species; grazing appears to have mixed impacts. U. brunneus is rare due to a combination of habitat specialization, competition, and anthropogenic impacts.

The howl of Rancho La Brea: Comparative anatomy of modern and fossil canid hyoid bones.

The Rancho La Brea (RLB) fossil collection housed at the La Brea Tar Pits and Museum in Los Angeles, California, is one of the richest collections of carnivoran fossils in the world. The collection is also particularly well known for the preservation of rare and understudied bones in the tar, including the small bony apparatus that is of particular interest to this study, the hyoid. The La Brea collection houses hyoids from several extinct carnivoran species, some of the most common being those of Canis dirus (the dire wolf) and Canis latrans (the coyote). In this study, we compare fossilized hyoid elements from these two canids to samples from modern large congeners, namely: Canis lupus (the gray wolf), Canis rufus (the red wolf), and modern C. latrans. Seven or nine measurements were taken on each bone of the hyoid apparatus, and principal component analyses were performed in order to determine statistical significance between species. For most of the bones, the majority of the variation was driven by size. Dire wolves could be clearly differentiated from all other canids for all elements; the hyoid apparatus of C. dirus is larger and more robust than that of C. lupus. Most of the bony elements could not be distinguished between red wolves or modern coyotes. However, there are enough, complete fossil coyote basihyoids to compare with those of their modern relatives, and in several metrics (both PC shapes and overall size), RLB and modern C. latrans are significantly different. As larger hyoids have been associated with a lower vocal frequency, this distinction would have resulted in the vocalizations of C. dirus occurring at a lower frequency than those produced by C. lupus and perhaps lower vocalizations in ice age coyotes than their modern relatives. RESEARCH HIGHLIGHTS: We quantify morphological differences in the hyoid of dire wolves (Canis dirus) relative to extant grey wolves (Canis lupus), and hypothesize that, as larger hyoids have been associated with a lower vocal frequency, the vocalizations of C. dirus might have occurred at a lower frequency than those by C. lupus. Likewise, modern and fossil coyotes (Canis latrans) show a significant difference in basihyoid size and shape, potentially indicating that modern and ancient coyotes might have sounded differently.

Starphenes and Phenes: Structures and Properties

Acenes have been known for a long time but their larger congeners, starphenes and phenes, have only been recently accessible as processable and characterizable derivatives. In this personalized review, we delineate the synthetic approach developed by our group over the last four years. Nickel-mediated Yamamoto coupling of ortho-dibromoacenes generates cyclotrimers. If performed in a shotgun approach, i.e. with substituted 2,3-dibromotetracene or -pentacene in the presence of ortho-dibromobenzene or ortho-dibromoveratrole, trimeric phenes and tetramers would result. Cyclotrimers formed by a pentacenylene and two phenylenes are formally dibenzo[a,c]hexacenes. A direct way to obtain these species is to employ Stille coupling of a dimethylstannafluorene with 2,3-dibromoacenes. If tetrabromoanthracenes or tetrabromopentacenes are fed into this process, tetrabenzopentacene and tetrabenzoheptacenes are easily accessible. Optical and quantum-chemical characterizations provide insight into the electronic situation and aromaticity of these species.

Vertical segregation of age-0 and age-1+ polar cod (Boreogadus saida) over the annual cycle in the Canadian Beaufort Sea

The offshore marine ecosystem of the Canadian Beaufort Sea faces the double pressure of climate change and industrialization. Polar cod (Boreogadus saida) is a pivotal forage species in this ecosystem, accounting for 95 % of the pelagic fish assemblage. Its vertical distribution over the annual cycle remains poorly documented. Hydroacoustic records from 2006 to 2012 were analysed to test the hypothesis that age-0 polar cod segregate vertically from larger congeners. Trawls and ichthyoplankton nets validated the acoustic signal. Fish length, weight, and biomass were estimated from new regressions of target strength and weight on standard length. Polar cod were vertically segregated by size in all months, with small age-0 juveniles in the epipelagic (<100 m) layer and larger age-1+ deeper in the water column. From December to March, the biomass of age-1+ peaked in a mesopelagic layer between 200 and 400 m. With increasing irradiance from April to July, the mesopelagic layer deepened and extended to 600 m. Starting in July, age-0 polar cod formed an epipelagic scattering layer that persisted until November. From September onward, age-0 left the epipelagic layer to join small age-1+ in the upper mesopelagic layer. Low biomass in the mesopelagic layer from February to September likely resulted from large polar cod settling on the seafloor to avoid diving marine mammals. Longer ice-free seasons, warmer sea-surface temperatures, or an oil spill at the surface would likely impact epipelagic age-0, while mesopelagic age-1+ would be vulnerable to an eventual oil plume spreading over and above the seafloor.

Evolution of enlarged body size of coal tits Parus ater in geographic isolation from two larger competitors, the crested tit Parus cristatus and the willow tit Parus montanus, on six Scandinavian islands.

ABSTRACTHere, we report that on six widely separated Scandinavian islands, the coal tit Parus ater has evolved morphologically in the direction of two absent competitors, the crested tit P. cristatus and the willow tit P. montanus, to the effect that it is up to 10% larger in linear dimensions than conspecifics on the adjacent Swedish mainland, where all three species coexist. The large size is genetically determined, as ascertained by clutch exchange experiments between island and mainland nests. We conclude that the increased size of P. ater in places where it is geographically isolated from its larger congeners is the result of evolutionary adaptation, due ultimately to relaxed interspecific competition. On the islands, P. ater has evolved into a medium-sized generalist, with selection pressures likely governed by the following causal relationships. When competitors are lacking, P. ater takes over the foraging space of the absentees. The enlarged food base allows higher population densities, which intensifies intraspecific interference competition. This, in turn, selects for increased body size. When P. ater coexists with its larger congeners, it occupies peripheral foraging sites in trees, which requires excellent manoeuvrability and energy-expensive locomotion modes. Reduction of body size increases locomotor capacity for mechanical and aerodynamic reasons and lowers energy consumption, so small size is favoured in sympatry. But in geographic isolation, P. ater exploits the tree periphery less and the inner tree regions more, and it also adopts the easier locomotion modes of the absent species. Therefore, selection for manoeuvrability and a small body size is relaxed. The new selection regime shifts the balance between opposing selection forces towards a larger body size. We were able to test 11 alternative hypotheses and available evidence conclusively eliminates them all. As a result, here, evolution could be predicted regarding both direction and amount of change.

A giant termite of the genus &lt;i&gt;Gyatermes&lt;/i&gt; from the late Miocene of Nagano Prefecture, Japan (Isoptera)

A new species of the termite genus &lt;em&gt;Gyatermes&lt;/em&gt; Engel &amp;amp; Gross (Archotermopsidae) is described and figured from a beautifully preserved forewing in late Neogene sediments of Nagano Prefecture, central Japan. The approximately 27-mm long forewing of &lt;em&gt;&lt;strong&gt;Gyatermes naganoensis&lt;/strong&gt;&lt;/em&gt; Engel &amp;amp; Tanaka, new species, is preserved in Late Miocene (late Messinian) mudstone of the Ogawa Formation (&lt;em&gt;ca&lt;/em&gt;. 6 Ma), and is distinguished from its slightly older and larger congener &lt;em&gt;G. styriensis&lt;/em&gt; Engel &amp;amp; Gross, from the early Tortonian of Styria, Austria. Comments are provided regarding the paleoclimatic implications of a giant termite in the Miocene fauna of Nagano.

Extreme habitat specialisation and population structure of two gorgonian-associated pygmy seahorses

Pygmy seahorses are a group of little-known miniature hippocampid fish that differ considerably in biology and ecology from their larger congeners. We estimated the population density, sex ratio and habitat of 2 sympatric, obligate gorgonian-associated pygmy seahorses, Hippocampus bargibanti and H. denise, in a 20 km long coastal marine protected area in southeast Sulawesi, Indonesia. Belt transects covering 200 m(2) each were surveyed at 7 sites and 5 depth contours to record the density of seahorses and their host gorgonians. The population density (+/- SE) was 1.17 (+/- 0.27) per 200 m(2) for H. denise and 0.34 (+/- 0.20) per 200 m(2) for H. bargibanti, some of the lowest densities for unexploited seahorse populations studied thus far. Male-female pairs (43.9%) were the most common group composition for H. denise, with single, 3 or 4 individuals found on 19.5, 7.3 and 29.3% of inhabited gorgonians, respectively. H. denise inhabited 7.8% of Annella reticulata gorgonians within the survey area but were recorded from a total of 8 gorgonian genera during extensive opportunistic ad hoc searches. Annella spp. density was 10.7 times higher than that of Muricella spp. (the sole host of H. bargibanti), of which 20.0% were inhabited. The small population size, occurrence of pygmy seahorses in groups on their hosts with the resulting skew in sex ratios, and habitat specialisation likely all impact the species' population dynamics, and hence these need to be considered in conservation management strategies.

Terrestrial versus aquatic phenotypes correlate with hydrological predictability of habitats in a semiterrestrial salamander (Urodela, Plethodontidae)

Terrestrial adaptations by small, desmognathine salamanders in Appalachian stream communities have been viewed as evolved responses to large, aquatic, predatory congeners. We tested the role of moisture in the development of adaptive phenotypes in the small, semiterrestrial Desmognathus ocoee . We measured indicators of relative ter- restrial vs. aquatic phenotypes (i.e. tolerance of desiccation, anatomical depression of body/tail) using individuals from stream habitats having different flow regimes within each of three geographical locations. Salamanders from intermittent, first-order streams exhibited greater desiccation tolerance, took longer to reach tolerance limits, and had more anatomically depressed bodies/tails than those from second-order, perennial streams, regardless of loca- tion. Phenotypes of salamanders from second-order streams showed aquatic tendencies. Phenotypic variation was consistent with relative habitat stability and not with relative abundance of large congeners. MtDNA analysis revealed that individuals grouped together based on geographical location and not habitat type, implying that the observed phenotypic differences arose in situ at each geographical location. Recent phylogenetic reconstructions of the Desmognathus indicate that large, aquatic forms are derived, and their appearance corresponds with the late Cenozoic development of modern Appalachian topography. We propose that radiation of desmognathine lifestyles and associated phenotypes tracked the formation of moisture-stability gradients associated with the creation of cool, wet, montane habitats. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 227- 238. ADDITIONAL KEYWORDS: adaptation - community - Desmognathus - moisture - terrestrial - variation.

Role of Food in Territoriality and Egg Production of Buffleheads (Bucephala Albeola) and Barrow's Goldeneyes (Bucephala Islandica)

Abstract Buffleheads (Bucephala albeola) and the North American population of Barrow's Goldeneyes (Bucephala islandica) typically breed in boreal and montane regions where food is less available relative to most habitats used by temperate nesting ducks. We investigated diets and digestive organ morphology of sympatrically breeding female Buffleheads and Barrow's Goldeneyes in central British Columbia. Because those congeners exhibit interspecific aggression in defense of breeding territories, we predicted that competition for food could be a principal factor in evolution of that behavior. We also hypothesized that breeding Buffleheads would show greater variation in digestive organ morphology than Barrow's Goldeneyes because of their smaller body size and consequently greater reliance on their diet to meet nutritional requirements for egg production. Both species fed predominantly on aquatic insects during all reproductive periods, particularly larvae of damselflies (Zygoptera), midges (Chironomidae), and phantom midges (Chaoborinae). Plant foods, primarily seeds of submergent and emergent vegetation, generally represented &lt;15% of diets in both species. Diets of breeding female Buffleheads and Barrow's Goldeneyes were similar throughout reproduction, hence competition for food has likely been a factor in evolution of territorial aggression between those species. The digestive tract morphology of Buffleheads was more variable than that of Barrow's Goldeneyes suggesting that the former relied more on dietary nutrients during reproduction than did their larger congener.

Why are shrews so small? The costs and benefits of small size in northern temperateSorex species in the context of foraging habits and prey supply

This paper reviews the ecological advantages and disadvantages of very small body size inSorex Linnaeus, 1758 shrews living at high latitudes with cold winters. It examines the feeding and foraging habits of small and large shrews in the context of prey supply, location of winter prey sources, territory requirements, habitat exploitation and inter-specific competition. Data on feeding habits and prey availability show that the major costs of small size are a reduction in food niche breadth and prey biomass resulting from restrictions on the type and size of prey eaten, and large territory requirements. Major benefits of small size are the ability to subsist on small, numerous and accessible arthropods with high encounter rates, enabling coexistence with larger congeners and exploitation of low-productivity habitats less suitable for larger earthworm-eating species. Small size, coupled with low per capita food intake, is shown to be of special adaptive value in cold winters when food supply is restricted mostly to small arthropods, and earthworms are few.

NATURAL HISTORY OF LEIOCEPHALUS SEMILINEATUS IN ASSOCIATION WITH SYMPATRIC LEIOCEPHALUS SCHREIBERSII AND AMEIVA LINEOLATA

We examined diet, habitat use, and behavior (focal animal observations of intraspecific interactions, escape behavior, and activity period) of Leiocephalus semilineatus from near Puerto Alejandro, Provincia de Barahona, República Dominicana, and compared some parameters to similar data collected at a site near Baní, Provincia de Peravia. Leiocephalus semilineatus is found in sympatry in dry scrub forests at both sites with Ameiva lineolata, an active-foraging teiid of approximately the same size, and at the Puerto Alejandro site with a larger congener, L. schreibersii. Leiocephalus semilineatus and L. schreibersii from Puerto Alejandro exhibited sexual size dimorphism, whereas L. semilineatus from the Baní site and A. lineolata did not. Leiocephalus semilineatus spent most of the time motionless; other observed activities were interactions with conspecifics, movement, and feeding. Lizards were active from shortly after sunrise to sundown, although activity peaked in late morning. Mean cloacal temperatures of L. semilineatus did not differ significantly from those of the other two species, but were significantly above ambient temperatures. Reproductive condition of collected specimens was examined and no correlation was found between snout-vent length and egg, follicle, or testis size. Clutch size was 1–2. Diets consisted primarily of invertebrates and did not differ significantly between the three species.

Probability of Intra- and Interspecific Encounters, and the Duration of Parental Care in &lt;I&gt;Nicrophorus investigator&lt;/I&gt; (Coleoptera: Silphidae)

In burying beetles (Nicrophorus), male and female pairs bury small carcasses to supply their larvae with food. Both parents care for their larvae for several days and defend them against other burying beetles that try to usurp the carcass. Male defense is very effective in preventing take-overs by conspecifics, but ineffective against attacks by larger congeners. From information on four species of Nicrophorus, Scott (1998) suggested that this asymmetry affects the duration of male care; males care longer when the major competitors are conspecifics, and leave early if they are larger congeners. We performed a field study examining the phenology of N. investigator Zetterstedt and its sympatric congeners in Bielefeld, Germany. Because of its relatively low abundance, an N. investigator arriving at a carcass had a much higher chance to meet an individual of another species of burying beetle than to meet a conspecific, suggesting that intraspecific competition is less important than competition by congeners. Breeding experiments showed that male care in N. investigator was shorter than in the numerically dominant species N. vespilloides Herbst and N. vespillo (L.), supporting Scott's hypothesis. However, we cannot exclude that the differences in male care were caused by other factors that vary between species, as for example the speed of larval development. Also, the probability of encounter used to estimate the relative importance of intra- and interspecific conflicts only gives a rough estimate of the competitive situation because of differences in fighting ability between species.

Some observations on the diet of the backswimmer, Anisops wakefieldi (Hemiptera: Notonectidae)

In a series of laboratory experiments, A. wakefieldi was presented with a variety of prey from different systems to investigate its potential for cannibalism and for eating cladocerans, copepods and rotifers. Large (ca. 7 mm) Anisops decreased the survivorship of small (ca. 3 mm) Anisops, but ate only 0.1 individual predator-1 d-1. Ingestion rates of small Anisops on small (<0.5 mm) and large (0.5–0.9 mm) Ceriodaphnia dubia were 53 and 28 individuals predator-1 d-1, while those of large Anisops on these prey were about twice as high. Clearance rates showed that small Anisops ate small and large C. dubia with similar efficiencies, while large Anisops ate large C. dubia much more efficiently. Anisops ate C. dubia much more efficiently than the calanoid copepod Boeckella hamata. Only the large Anisops ate adult B. hamata. Large Anisops had a very low ingestion rate (0.6 individuals predator-1 d-1) on the larger congener, B. triarticulata. Small, but not large, Anisops ate the rotifer Synchaeta pectinata and small Anisops presented with a natural assemblage of rotifers ate S. pectinata and Polyarthra dolichoptera, but not four other species with a more well-developed lorica – Anuraeopsis fissa, Brachionus angularis, Keratella cochlearis and K. slacki. Ingestion rates on Synchaeta and Polyarthra were 14–20 individuals Anisops -1 d-1.

Echolocation and foraging behavior of the lesser bulldog bat, Noctilio albiventris : preadaptations for piscivory?

We studied variability in foraging behavior of Noctilio albiventris (Chiroptera: Noctilionidae) in Costa Rica and Panama and related it to properties of its echolocation behavior. N. albiventris searches for prey in high (>20 cm) or low (<20 cm) search flight, mostly over water. It captures insects in mid-air (aerial captures) and from the water surface (pointed dip). We once observed an individual dragging its feet through the water (directed random rake). In search flight, N. albiventris emits groups of echolocation signals (duration 10–11 ms) containing mixed signals with constant-frequency (CF) and frequency-modulated (FM) components, or pure CF signals. Sometimes, mostly over land, it produces long FM signals (duration 15–21 ms). When N. albiventris approaches prey in a pointed dip or in aerial captures, pulse duration and pulse interval are reduced, the CF component is eliminated, and a terminal phase with short FM signals (duration 2 ms) at high repetition rates (150–170 Hz) is emitted. Except for the last pulses in the terminal phase N. albiventris avoids overlap between emitted signals and echoes returning from prey. During rakes, echolocation behavior is similar to that in high search flight. We compare N. albiventris with its larger congener, N. leporinus, and discuss behavioral and morphological specializations that can be interpreted as preadaptations favoring the evolution of piscivory as seen in N. leporinus. Prominent among these specializations are the CF components of the echolocation signals which allow detection and evaluation of fluttering prey amidst clutter-echoes, high variability in foraging strategy and the associated echolocation behavior, as well as morphological specializations such as enlarged feet for capturing prey from the water surface.

Body Size, Prey Size, and Community Structure in Insectivorous Mammals

This study investigates the relationship between body size and prey size in three two—species communities of insectivorous mammals in Australia and England. In capacity all species maximized their net energy intake by feeding preferentially on large prey, but the field in larger species of insectivore in each community ate prey that were 25—29% longer than those eaten by smaller species. Direct field observations showed that the larger species of insectivores dug extensively in the topsoil and subsurface litter to obtain prey, whereas the smaller species foraged on the litter surface or in trees. The larger species also exploited denser and structurally more complex microhabitats than their smaller relatives. These differences in foraging behavior allowed their larger insectivores in each community to exploit prey that were 7—19% longer than those encountered by the smaller species. Controlled removal of the larger species of insectivore from two communities produced marked changes in the microhabitat use and prey size selection of the remaining species. In the first community, a small eutherian shrew (Sorex minutus) ate more long prey and tended to move into tall grass when a larger congener, S. araneus, was removed. In the second community a small dasyurid marsupial (Antechinus stuartii) also ate more long prey and decreased its use of trees when the larger A. swainsonii was removed. These results provide no evidence that body size directly influences prey size selection in insectivorous mammals. However, body size differences may influence prey size selection indirectly by conferring an asymmetric competitive advantage on larger insectivores, thus allowing them to actively exclude smaller species from microhabitats containing larger prey. Community diversity of insectivorous mammals should therefore depend on the availability of different foraging microhabitats, and not on the distribution of prey sizes.