Morphological and behavioral defenses in dragonfly larvae: trait compensation and cospecialization

Many animals have two basic traits for avoiding being killedby a predator: behavioral modification and morphological defense.We examined the relationship between antipredator behavior andmorphological defense in larvae of three closely related dragonflyspecies within the genus Leucorrhinia. The three species differwith regard to their morphological defense as expressed in thelength of the larval abdominal spines. Results showed that longerabdominal spines provided protection against an attacking fishpredator (perch) because the probability of being rejected afteran attack was significantly higher in the species with the longestabdominal spines. In contrast to other studies, the specieswith the strongest morphological defense did not show the leastbehavioral predator avoidance. Instead, the species with intermediatemorphological defense showed the least predator behavioral avoidance.The results suggest that the Leucorrhinia system is a mixtureof trait cospecialization (a positive correlation between antipredatorbehavior and morphological defense) and trait compensation (anegative correlation between antipredator behavior and morphologicaldefense). Differences in the relationship between morphologicaland behavioral defense between species might be related to abundancepatterns of the three species in lakes with and without fishpredators.     

Polymorphic microsatellite loci to study population dynamics in a dragonfly,the libellulid Trithemis arteriosa (Burmeister, 1839)

One of the most widely distributed dragonfly species in Africa is the red‐veined‐dropwing Trithemis arteriosa. It is an indicator for permanent water bodies, which are freshwater ecosystems of high environmental value especially in arid regions. For studies to determine population structures, assess species viability and monitor environmental changes, a panel of 10 polymorphic microsatellite loci was developed. The number of alleles per locus ranged from four to 12, with an observed heterozygosity ranging from 0.149 to 0.843.     

The development of dragonfly larvae (Odonata: Anisoptera) from two streams in north-eastern Victoria, Australia

Developmental stages of larvae of eight species of Anisoptera from the Kiewa River and Middle Creek, Victoria, were determined and their phenology investigated. The last six to nine instars of each species were distinguished by size frequency and scatter plots, using labium width, metafemur and wing-pad measurements, and the early instars were estimated from Dyar's Law. This suggested between 11 to 14 instars. Four species appeared to be univoltine and four species semivoltine.     

The macrophyte, Stratiotes aloides, protects larvae of dragonfly Aeshna viridis against fish predation

Predation could be one force determining which contemporary species occupy a certain habitat. Aeshna viridis is an endangered dragonfly species with a larval distribution strongly associated with lakes where the water plant, water soldier, Stratiotes aloides, occurs. In this study, the larvae were almost exclusively found in patches of S. aloides. To study larval association with S. aloides further, we conducted a series of laboratory experiments. Behavioural experiments indicated that larvae preferred S. aloides. Aeshna viridis larvae were nocturnal and rather inactive. Larvae on S. aloides were less susceptible to predation by the perch, Perca fluviatilis, than larvae on another water plant, Myriophyllum alterniflorum. According to our study it seems that occurrence of S. aloides may limit the distribution of A. viridis, and the protection of refuges may be essential in planning the conservation of this endangered species.     

Density-dependent population dynamics in larvae of the dragonfly Pachydiplax longipennis: a field experiment

Summary Several features of dragonfly population biology suggest that population regulation occurs in the larval stage. This study was designed to determine if density-dependent interactions among larval odonates can affect survival, growth and emergence. First-instar larvae of the dragonfly Pachydiplax longipennis were raised in outdoor experimental ponds at initial densities of 38, 152, and 608 larvae · m^-2, under two levels of food availability. Food availability was supplemented in half the pools by volumetric addition of zooplankton every other day. Pools in the low food treatment did not receive the zooplankton supplement.There was a strong negative effect of density on the mean growth rate of survivors, which included both emerging tenerals and individuals overwintering in the larval stage. A higher proportion emerged from low density than high density pools. Metamorphs from high density populations were smaller and emerged slightly later than those from low density, but the absolute number of metamorphs did not differ significantly among density treatments. Food supplementation significantly increased the proportion of overwintering larvae. There were no significant food-by-density interactions, indicating that food and density acted independently on larval population dynamics. Density-dependent mechanisms can clearly contribute to odonate population regulation, especially by controlling the number of larvae which emerge and the average age at reproduction. Population-level responses to density may be a result of interference among larvae.     

Micro-morphological adaptations of the wing nodus to flight behaviour in four dragonfly species from the family Libellulidae (Odonata: Anisoptera)

Adult dragonflies can be divided into two major groups, perchers and fliers, exhibiting notably different flight behaviour. Previous studies have yielded conflicting results regarding the link between the wing macro-morphology and flight style in these two groups. In this study, we present the first systematic investigation of the micro-morphological differences of wings of percher and flier dragonflies in four closely related species from the family Libellulidae. Our results suggest that the shape and material composition of wing microstructural components and, in particular, the nodus are adapted to facilitate the specific wing functioning in fliers and perchers. The findings further indicate a decreasing trend in the area proportion of the soft resilin-dominated cuticle in the nodus in the series of species from typical perchers to typical fliers. Such a reduction in the resilin proportion in the nodus of fliers is associated with an increase in the wing aspect ratio. The knot-shaped protrusion at the nodus of perchers, which becomes notably smaller in that of strong fliers, is likely to act as a mechanical stopper, avoiding large wing displacements. This study aims to develop a novel framework for future research on the relationship between wing morphology and flight behaviour in dragonflies.     

Correlation between population dynamics of mosquito larvae and their habitat qualities

Surveillance of anopheline and culicine larvae was conducted fortnightly to determine population composition and density at seven sites in the area of the Mathura Refinery, Mathura, India during 2005–2006. The correlation between population of the vectors and their habitat quality was established. Temperature (0.978 and 0.85°C), pH (0.99 and 0.95), conductivity (0.98 and 0.98 mho) and calcium ion hardness (0.978 and 0.85 p.p.m.) were positively correlated with the populations of both larval species. In contrast, the correlation coefficients between the parameters total hardness, magnesium ion hardness, biochemical oxygen demand and chemical oxygen demand varied with the larval species. The anopheline larval population was dominant over the culicine population in the surveillance area. The distribution of anopheline mosquito larvae during the study period was found to be constant, and the average density of anopheline and culicine larvae was 84.70 and 15.30%, respectively, across all seven sites. Thus, the study demonstrated spatial and temporal population differences of mosquito larvae with respect to environmental factors, including water quality.     

The distribution patterns of dragonflies (Insecta: Odonata) along the Kiewa River,Australia, and their relevance in conservation assessment

Sampling of larval and adult Odonata from 16 sites along the Kiewa River, Victoria, yielded 34 species: 10 Zygoptera, 24 Anisoptera. Patterns of larval and adult incidence were appraised, and showed that most species were restricted in incidence to several consecutive sites along the river, and that there is clear distinction also between the faunas of the potamon, rhithron and eucrenon regions. Different species of some genera of Anisoptera displayed different zonational distributions, and patterns of incidence and relative abundance of larvae and adults confirmed zonational occupancy. For larvae, these distribution patterns transcended the mode of collection, although many species were found most abundantly in one microhabitat or by one of several sampling methods employed at each site. Sampling of the two stages separately showed considerable concurrence of distributional patterns, so that either stage alone may provide data of value in faunal and conservation assessment. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ecological principles of species distribution models: the habitat matching rule

Most species distribution models (SDMs) assume that habitats are closed, stable and without competition. In that environmental context, it is ecologically correct to assume that members of a species will be distributed in direct relation to the suitability of the habitat, that is, according to the so‐called habitat matching rule. This paper examines whether it is possible to maintain the assumption of the habitat matching rule in the following circumstances: (1) when habitats are connected and organisms can move between them, (2) when there are disturbances and seasonal cycles that generate instability, and (3) when there is inter‐specific and intra‐specific competition. Here I argue that it is possible as long as the following aspects are taken into account. In open habitats at equilibrium, in which habitat selection and competition operate, the habitat matching rule can be applied in some conditions, while competition tends to homogenize the species distribution in other environmental contexts. In the latter case, two methods can be used to incorporate these effects into SDMs: new parameters can be incorporated into the response functions, or the occurrence of proportions of categories of individuals (adult/young, male/female, or dominant/subordinate species in guilds) can be used instead of the occurrence of organisms. The habitat matching rule is not fulfilled in non‐equilibrium environments. The solution to this problem lies in the design of SDMs with two strategies that depend on scale. Locally, the disequilibrium can be encapsulated using average environmental conditions, with sufficiently large cells (in the case of metapopulations) and/or long enough sampling periods (in the case of seasonal cycles). At coarse scales, the use of presence‐only models can in some cases avoid the destabilizing effect of catastrophic historical processes. The matching law is a strong assumption of SDMs because it is based on population ecology theory and the principle of evolution by natural selection.     

A systematic relationship between phytochrome-controlled development and species habitat,for plants grown in simulated natural radiation

A survey of the responsiveness of plant species, typical of open and shade habitats, to simulated natural shade-light quality (i.e. white light plus supplementary far-red) has demonstrated a systematic relationship between habitat and certain developmental responses. Supplementary far-red light has a much greater effect on stem extension rate, petiole length, and leaf dry weight: stem dry weight ratio of the open habitat, shade-intolerant species. Far-red effects on leaf chlorophyll content show no such systematic grading. These results are discussed in relation to habitat adaptation. In most cases, the relationship between developmental response and the estimated phytochrome photoequilibrium, which is established by the radiation treatment, is linear. This is taken as an indication of phytochrome involvement in shade perception.Abbreviations P _fr far-red light absorbing form of phytochrome - P _total total phytochrome - PAR photosynthetically active radiation Paper 8 in the series The Function of Phytochrome in the Natural Environment; for paper 7 see Morgan and Smith (1978)     

Predicting species distribution: offering more than simple habitat models

In the last two decades, interest in species distribution models (SDMs) of plants and animals has grown dramatically. Recent advances in SDMs allow us to potentially forecast anthropogenic effects on patterns of biodiversity at different spatial scales. However, some limitations still preclude the use of SDMs in many theoretical and practical applications. Here, we provide an overview of recent advances in this field, discuss the ecological principles and assumptions underpinning SDMs, and highlight critical limitations and decisions inherent in the construction and evaluation of SDMs. Particular emphasis is given to the use of SDMs for the assessment of climate change impacts and conservation management issues. We suggest new avenues for incorporating species migration, population dynamics, biotic interactions and community ecology into SDMs at multiple spatial scales. Addressing all these issues requires a better integration of SDMs with ecological theory.     

Agonistic behaviour in final-instar larvae of Austrolestes colensonis (Odonata: Lestidae)

Abstract

The agonistic displays of Austrolestes colensonis larvae are described. A terminology is developed to classify larval agonistic displays in the family Lestidae.     

Distribution and habitat specialization of species affect local extinction in dragonfly Odonata populations

The object of our study was to determine the effect of distribution and habitat specialization of odonate species on local extinction in streams in central Finland. We studied the local extinction of the 20 most abundant dragonfly (Odonata) species in 34 small creeks and brooks in central Finland. The historical presence of each studied species in our research area was confirmed using existing records gathered between 1930 and 1975. A minimum of five records was available for each species. During the summers of 1995 and 1996, we investigated the current persistence of 219 separate populations with historical presence. In total, 98 historical populations were vanished. As predicted, we found that species with a narrow distribution were less persistent than species with a broad distribution. Therefore, the extinction risk of a species was inversely related to the width of its regional distribution. Using reference works, species were categorized into two main breeding habitat types: lotic species or lentic species. The species main habitat type was a significant predictor of local extinction risk after statistical removal of the effect of regional distribution on extinction risk. The lotic species had lower local extinction risk than other species. Altogether, the highest extinction risk was found in habitat-specialist species associated with peatlands, probably due to loss of natural breeding habitat. On the other hand, extinction risk was lower in widely distributed habitat generalist species than true lotic species. The local extinction within species was more common in small dynamic upstream than in larger stable downstream habitats. The results of this study are consistent with meta-population theory.     

Ranging behaviour and habitat usage in black rhinoceros, Diceros bicornis, in a Kenyan sanctuary

Home range area and habitat utilization by translocated black rhinoceros Diceros bicornis were studied at Sweetwaters Rhino Sanctuary in the Laikipia district of Kenya. Home ranges were estimated from sightings and tracking data; home range area was very variable between individuals (range 2.25–14.39km², minimum convex polygons), and was independent of age or sex. Groups of rhinoceros shared common home ranges, with little or no overlap between groups; each group consisted of one adult male, one or more adult females and their calves, and sometimes immature animals. Rhinoceros utilize a variety of habitats, but within these show positive selection for certain habitats. Home ranges generally included more Euclea bush, and less grassland and Acacia bush than expected. Rhinoceros make use of regular resting places, or bedding sites, generally situated in bushland in secluded areas, often in dense thickets. Rhinoceros defaecate at dung piles or middens. Middens are located throughout the range not just on the boundaries; the highest density of middens was found in riverine woodland, and the lowest density in grassland and Acacia bush.     

Effects of longitudinal variations in stream habitat structure on fish abundance: an analysis based on subunit-scale habitat classification

SUMMARY 1. Stream reaches contain assortments of various habitat types that can be defined at different spatial scales, such as channel unit (e.g. pools, riffles) and subunit (patches within channel units). We described longitudinal (upstream–downstream) patterns of stream habitat structure by considering subunits as structural elements, and examined their effects on the abundance of masu salmon ( Oncorhynchus masou ) and rosyface dace ( Leuciscus ezoe ) in a third-order tributary of the Teshio River in northern Hokkaido, Japan.
2. Nine subunit types were determined on the basis of water depth, current velocity and substrate, using 0.5 × 0.5 m grids. Although both masu salmon and rosyface dace used pools as a major habitat, the former preferred a subunit type occurring at pool heads (PH subunit) while the latter preferred a slow-current edge type (SE-2 subunit).
3. Along the course of the stream, slow-edge subunits (SE-1, 2 and 3) increased in frequency downstream while fast-edge subunits (FE-1 and 2) decreased, suggesting a downstream development of slow-current edges. Regression analyses indicated that longitudinal variation in masu salmon abundance was explained by the area of PH, rather than pools. Masu salmon density increased with the area of PH. Rosyface dace abundance was explained by a combination of water depth and the area of SE-2, both effects being positive.
4. Longitudinal variations in the abundance of both species were related to the abundance of their preferred habitat at the subunit scale, rather than channel-unit scale. The results emphasise the importance of fine-scale patchiness when examining stream fish habitats.     

Species-specific habitat distribution of coral reef fish assemblages in relation to habitat characteristics in an Okinawan coral reef

We determined the species-specific habitat associations of coral reef fishes and environmental characteristics in an Okinawan coral reef in Japan. We focused on three families (Pomacentridae, Gobiidae and Labridae) and attempted to determine differences in habitat utilization. We selected six sites along the coast of Amitori Bay, from the entrance to the innermost part, in order to cover a wide range of habitat characteristics (exposed habitat, semi-exposed habitat and sheltered habitat). The species diversity of coral assemblages was greater at the exposed and semi-exposed habitats, whereas branching coral mostly covered the sheltered habitat. The environmental factors that determine the species-specific spatial association in fishes differed among families. Both biological characteristics (coral morphology and coral species diversity) and physical characteristics (water depth and wave exposure) affected the spatial association of pomacentrids and gobiids. In contrast, physical characteristics such as substrate complexity and water depth affected the species-specific spatial association of labrid species. Further study is needed to determine the ecological factors that regulate the species-specific habitat preference in Okinawan coral reefs.     

Influence of egg size differences within egg clutches on larval parameters in nine libellulid species (Odonata)

Abstract.  1. In libellulids, egg size differs between species and populations. There are also size differences within egg clutches of individual females.
2. Past experiments suggest that there are two different types of egg clutches in libellulids. Egg size decreases significantly during oviposition in species that perform non-contact guarding during oviposition. In contrast, in species ovipositing in tandem, egg size is randomly distributed.
3. This study deals with the possible consequences of egg size variation within the different egg clutch types. The study examined whether there is a correlation between egg development time, offspring sex or larval size and egg size.
4. The current experiments were conducted in Namibia and Germany. Five non-contact guarding and four tandem guarding libellulid species were used.
5. In some species larger eggs needed more time to develop, in some species no correlation between egg size and egg development time could be found, whereas in other species larger eggs developed faster.
6. The sex ratio was biased towards females in Leucorrhinia dubia and in Sympetrum striolatum and egg size was not associated with gender.
7. In both egg clutch types larger eggs resulted in larger larvae. In this study, evidence was found that the effects of egg size diminished with progressing larval development under good conditions. However, it is possible that the effects may have a greater influence under harsh circumstances.     

Habitat characteristics and the distribution of Odonata in a lowland river catchment in eastern England

The influence of habitat characteristics on the distribution of larval and adult Odonata communities in a lowland river in eastern England was studied. There was a longitudinal distribution of Odonata, with larval assemblages being influenced directly by marginal flow velocity, biochemical oxygen demand (BOD) and phosphate concentrations and indirectly by shade and cover of floating vegetation. Adult populations responded directly to shade, reed cover, amenity-managed land use and bank height, and indirectly to BOD and ammonia concentrations. Distribution patterns were strongly associated with both natural changes along the river system and management impacts. River management practices locally disrupted the natural displacement of species along the river, but whilst some forms of human interference on river systems were beneficial to species richness, the effects on stenotopic species were disadvantageous. To conserve Odonata management emphasis should be on the maintenance of suitable conditions for river specialists.