Does microhabitat structure affect foliar mite assemblages?

1. Habitat structure is an important factor influencing population dynamics and trophic organisation of terrestrial invertebrates. The phylloplane zone on vascular plant leaves is topographically complex, containing a multitude of microhabitats such as leaf hairs, lesions, and structural refugia such as domatia, which may modify interactions between resident invertebrate communities, colonisers, and subsequent trophic relationships. Leaf domatia are small indentations on the underside of leaves and are often inhabited by potentially beneficial mites and other arthropods. 2. This study investigated the relationship between domatia availability and foliar mite assemblages in contrasting habitats (native forest, plantation forest, and pasture) using a standard test plant (the endemic New Zealand shrub Coprosma lucida, J.R. & G. Forst.). 3. Diverse woody native vegetation types supported higher numbers of mite species than either plantation forest or pastoral grasses. The highest number of mite species occurred in the native forest (63%), plantation forest (38%), and pastoral grasses (25%). In the native vegetation type, experimental C. lucida leaves with domatia supported higher mite densities, greater colonisation success, and more diverse mite assemblages than those without domatia. Mite assemblages within the pastoral site were significantly different from the other two vegetation types. Only one fungivorous mite species, Orthotydeus californicus, occurred compared to five mite species in native and plantation forests. 4. This study indicated that foliar mite assemblages in native vegetation on experimental C. lucida shrubs are influenced by domatia availability, resident foliar mites, and local mite assemblages.     

Does canopy position affect wood specific gravity in temperate forest trees?

The radial increases in wood specific gravity known in many tree species have been interpreted as providing mechanical support in response to the stresses associated with wind loading. This interpretation leads to the hypothesis that individuals reaching the canopy should (1) be more likely to have radial increases in specific gravity and (2) exhibit greater increases than individuals in the subcanopy. Wood specific gravity was determined for three species of forest trees (Acer rubrum, Fagus grandifolia and Tsuga canadensis) growing in central Massachusetts, USA. Acer rubrum shows radial increases in specific gravity, but these increases are not more pronounced in canopy trees; the other two species show a pattern of radial decreases. The degree of radial increase or decrease is influenced by tree height and diameter. Of the dominant tree species for which we have data, A. rubrum, Betula papyrifera and Pinus strobus show radial increases in specific gravity, whereas F. grandifolia, T. canadensis and Quercus rubra show decreases. The occurrence of radial increases in B. papyrifera and P. strobus, which are often canopy emergents, suggests that it is overall adaptive strategy that is important rather than position (canopy vs. subcanopy) of any individual tree. It is suggested that radial increases in specific gravity are associated with early-successional status or characteristics and decreases with late-successional status or persistence in mature forest.     

Does richness of emergent plants affect CO2 and CH4 emissions in experimental wetlands?

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Do terrestrial invertebrates experience floodplains as landscape mosaics? Immediate and longer-term effects of flooding on ant assemblages in a floodplain forest

Considering the floodplain landscape as a mosaic of habitat patches at different successional stages is useful for understanding (1) the processes associated with individual floods and (2) the legacy of flood history. Here, we investigate the applicability of the mosaic model to opportunistic ant species inhabiting the floodplain. Ground-active ant assemblages in river red gum (Eucalyptus camaldulensis) floodplain forest in south-eastern Australia were sampled before and for two years after a major flood in 2000–2001 at 24 sites with different inundation histories. Despite the mobility and opportunistic life history traits of floodplain ants, flood history appeared to impose a persistent mosaic structure on ant assemblages. Increasing duration of inundation of the forest floor was associated with decreasing species richness. β-diversity was low, with the ant species at the most inundation-prone sites being a subset of those at drier sites. Less extensive flooding occurred in 2002–2003, enabling the consistency of short-term responses to inundation to be assessed. Flooding acts as a resetting mechanism, creating a characteristic ant assemblage. After floodwaters receded, there was little evidence of convergence in the structure of ant assemblages through time between sites flooded for different durations. The persistence of dissimilarities in ant assemblages suggests that succession towards terrestrialization was either not occurring or that it was operating at a rate that was too slow to be detected.     

Does fragmentation of wetlands affect gene flow in sympatric Acrocephalus warblers with different migration strategies?

Wetlands are naturally patchy habitats, but patchiness has been accentuated by the extensive wetlands loss due to human activities. In such a fragmented habitat, dispersal ability is especially important to maintain gene flow between populations. Here we studied population structure, genetic diversity and demographic history of Iberian and North African populations of two wetland passerines, the Eurasian reed warbler Acrocephalus scirpaceus and the moustached warbler Acrocephalus melanopogon. These species are closely related and sympatric in our study sites, but the reed warbler is a widespread long‐distance migrant while the moustached warbler's breeding range is patchier and it is resident or migrates over short distances. Using microsatellite and mtDNA data, we found higher differentiation in moustached than in reed warblers, indicating higher dispersal capability of the latter species. Our results also suggest that the sea limits dispersal in the moustached warbler. However, we found evidence of gene flow between the study sites in both species, indicating a capability to compensate for habitat fragmentation. In most cases, the gene flow was restricted, possibly because of the large distances between study sites (from ca 290 to 960 km) or breeding site fidelity. The reed warbler had higher haplotype diversity, likely due to dispersal from different populations, past admixture event and a larger population size. We found also signs of postglacial population growth for both species and evidence of a recent colonization or re‐colonization of the Mallorca Island by the moustached warbler.     

Will fencing floodplain and riverine wetlands from feral pig damage conserve fish community values?

Installation of feral pig (Sus scrofa) exclusion fences to conserve and rehabilitate coastal floodplain habitat for fish production and water quality services remains untested. Twenty‐one floodplain and riverine wetlands in the Archer River catchment (north Queensland) were surveyed during postwet (June–August) and late‐dry season (November–December) in 2016, 2017, and 2018, using a fyke net soaked overnight (~14–15 hr) to test: (a) whether the fish assemblage are similar in wetlands with and without fences; and (b) whether specific environmental conditions influence fish composition between fenced and unfenced wetlands. A total of 6,353 fish representing twenty‐six species from 15 families were captured. There were no wetland differences in fish assemblages across seasons, years and for fenced and unfenced (PERMANOVA, Pseudo‐F < 0.589, p < .84). Interestingly, the late‐dry season fish were far smaller compared to postwet season fish: a strategy presumably in place to maximize rapid disposal following rain and floodplain connectivity. In each wetland, a calibrated Hydrolab was deployed (between 2 and4 days, with 20 min logging) in the epilimnion (0.2 m) and revealed distinct diel water quality cycling of temperature, dissolved oxygen and pH (conductivity represented freshwater wetlands), which was more obvious in the late‐dry season survey because of extreme summer conditions. Water quality varied among wetlands in terms of the daily amplitude and extent of daily photosynthesis recovery, which highlights the need to consider local conditions and that applying general assumptions around water quality conditions for these types of wetlands is problematic for managers. Though many fish access wetlands during wet season connection, the seasonal effect of reduced water level conditions seems more overimprovised when compared to whether fences are installed, as all wetlands supported few, juvenile, or no fish species because they had dried completely regardless of the presence of fences.     

Does within-population variation in fish egg size reflect maternal influences on optimal values?

Various models that assume correlations between maternal phenotype and offspring environment predict adaptive variation in egg size within populations. Here we conduct a comparative test of these models using published data on fish egg size. Intrapopulation variation in egg size was most pronounced in fish with demersal eggs and larvae (median coefficient of variation [CV] at family level = 6.5%), where offspring environment is likely influenced by maternal phenotype, and least so in fish with pelagic eggs (CV = 3.6%), which experience a relatively stochastic spatial distribution during incubation. This difference was significant at various taxonomic levels, was robust to variation in mean egg size and habitat (i.e., freshwater or marine), and was mirrored in independent paired contrasts. Fish with demersal eggs and pelagic larvae were not significantly different from those with pelagic eggs (CV = 3.8%), indicating that selection favoring within-population variation in egg size occurs mainly posthatching and that any such selection occurring prehatching may be less intense. These results suggest that patterns of within-population variation in egg size among fish taxa reflect adaptive processes and that maternal effects on the egg size-fitness function may explain apparent discrepancies from the single-optima Smith-Fretwell model.     

Does breeding season variation affect evolution of a sexual signaling trait in a tropical lizard clade?

Sexually selected traits can be expected to increase in importance when the period of sexual behavior is constrained, such as in seasonally restricted breeders. Anolis lizard male dewlaps are classic examples of multifaceted signaling traits, with demonstrated intraspecific reproductive function reflected in courtship behavior. Fitch and Hillis found a correlation between dewlap size and seasonality in mainland Anolis using traditional statistical methods and suggested that seasonally restricted breeding seasons enhanced the differentiation of this signaling trait. Here, we present two tests of the Fitch–Hillis Hypothesis using new phylogenetic and morphological data sets for 44 species of Mexican Anolis. A significant relationship between dewlap size and seasonality is evident in phylogenetically uncorrected analyses but erodes once phylogeny is accounted for. This loss of strong statistical support for a relationship between a key aspect of dewlap morphology and seasonality also occurs within a species complex (A. sericeus group) that inhabits seasonal and aseasonal environments. Our results fail to support seasonality as a strong driver of evolution of Anolis dewlap size. We discuss the implications of our results and the difficulty of disentangling the strength of single mechanisms on trait evolution when multiple selection pressures are likely at play.     

Is there a core set of organisms that structure macroinvertebrate assemblages in freshwater wetlands?

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Does divergence in female mate choice affect male size distributions in two cave fish populations?

Sexual selection by female choice can maintain male traits that are counter selected by natural selection. Alteration of the potential for sexual selection can thus lead to shifts in the expression of male traits. We investigated female mate choice for large male body size in a fish (Poecilia mexicana) that, besides surface streams, also inhabits two caves. All four populations investigated, exhibited an ancestral visual preference for large males. However, only one of the cave populations also expressed this female preference in darkness. Hence, the lack of expression of female preference in darkness in the other cave population leads to relaxation of sexual selection for large male body size. While P. mexicana populations with size-specific female mate choice are characterized by a pronounced male size variation, the absence of female choice in one cave coincides with the absence of large bodied males in that population. Our results suggest that population differences in the potential for sexual selection may affect male trait variation.     

Do steady state assemblages occur in shallow lentic environments from wetlands?

The Okavango Delta has an annual flood cycle that spreads slowly from the northwestern`panhandle' into a widening delta to the southeast. Rotifers were sampled from areas where the flood was active, and from other areas not yet reached by the flood. In still waters, the samples were dominated by euplanktonic rotifers, particularly of the genera Brachionus, Keratella and Hexarthra, with about 20 species per 1000 individuals at a station. Where the water was moving the samples were dominated by periphytic rotifers, with over 100 species per 1000 individuals at a single station. The periphytic species were dominated by the genus Lecane,with over 45 species, followed by Lepadellawith 24 species, and Trichocercawith 23 species. Comparison of the Okavango with six other tropical localities reveals fairly consistent ratios of the numbers of species in the periphytic genera Lecane, Lepadellaand Trichocerca,indicating that there may be assembly rules for communities of tropical periphytic rotifers.     

Evaluating detectability of freshwater fish assemblages in tropical streams: Is hand-seining sufficient?

Unprecedented threats to natural ecosystems mean that accurate quantification of biodiversity is a priority, particularly in the tropics which are underrepresented in monitoring schemes. Data from a freshwater fish assemblage in Trinidad were used to evaluate the effectiveness of hand-seining as a survey method in tropical streams. We uncovered large differences in species detectability when hand-seining was used alone, in comparison with when hand-seining and electrofishing were used together. The addition of electrofishing increased the number of individuals caught threefold, and increased the biomass fivefold. Some species were never detected using hand-seining, resulting in significant underestimates of species richness; rarefaction curves suggest that even when hand-seining effort increases, species richness is still underestimated. Diversity indices (Shannon and Simpson index) reveal that diversity was also significantly lower for hand-seined samples. Furthermore, the results of multivariate analyses investigating assemblage structure also differed significantly depending on whether they were based on hand-seined data alone, or a combination of hand-seining and electrofishing. Despite the extra equipment and maintenance required, these findings underline the value of including electrofishing when sampling tropical freshwater streams.     

Does structural change in the zooplankton community affect larval fish feeding in anthropogenically disturbed tropical waters?

Environmental Biology of Fishes - Anthropogenic perturbations and climate change have altered the zooplankton community structure in the Klang Strait during the past 30&nbsp;years, in that the...     

Does variation in morphology correspond with variation in habitat use in freshwater gastropods?

We tested if variations (i.e., breadth) in morphology and habitat use vary predictably among six aquatic gastropod species that were collected across Indiana and Illinois, USA. We predicted that interspecific morphological variation would positively covary with variation in habitat use among species. We used geometric morphometrics (Procrustes technique and relative warp analysis) to quantify morphology and multivariate analyses (PCA) to quantify habitat. Increased morphological breadth did not vary predictably with increased habitat breadth. However, we found that life history traits correspond with patterns in morphological and habitat breadth for these six aquatic gastropods. Pulmonate gastropods (use lungs for respiration) that lack an operculum cover exhibited decreased morphological breadth compared to coenogastropods (use gills for respiration). This pattern may ultimately be a function of behavioral adaptations in freshwater gastropods. Gastropods that are capable of breathing air or using other behavioral modifications such as burrowing to escape predators may not require high morphological breadth. Conversely, selection may favor higher morphological breadth in gastropods with gills that also do not move out of the water column to escape predators.     

Niche expansion and the niche variation hypothesis: does the degree of individual variation increase in depauperate assemblages?

The niche expansion and niche variation hypotheses predict that release from interspecific competition will promote niche expansion in depauperate assemblages. Niche expansion can occur by different mechanisms, including an increase in within-individual, among-individual, or bimodal variation (sexual dimorphism). Here we explore whether populations with larger niche breadth have a higher degree of diet variation. We also test whether populations from depauperate lizard assemblages differ in dietary resource use with respect to variation within and/or among individuals and sexual dimorphism. We found support for the niche expansion and niche variation hypotheses. Populations in assemblages with low phylogenetic diversity had a higher degree of individual variation, suggesting a tendency for niche expansion. We also found evidence suggesting that the mechanism causing niche expansion is an increase in variation among individuals rather than an increase in within-individual variation or an increase in bimodal variation due to sexual dimorphism.     

Does post-warm-up rest interval affect the diurnal variation of 30-s Wingate cycle ergometry?

The purpose of this investigation was to assess the effects of rest interval following active warm-up (WU) durations on the diurnal variation of high-intensity cycling performance. Eleven male physical education students (22.6 ± 2.5 years; 179.2 ± 5.7 cm; 82.6 ± 9.6 kg; mean ± SD) participated in a cross-over randomized study, and they all underwent the 30-s Wingate test in the morning (08:00 h) and in the evening (18:00 h), after 5-min (WU₅) and 15-min (WU₁₅) warm-up durations, either with rest (WR), or without rest interval (NR) separating the WU at the onset of the high-intensity cycling exercise performance. The WU consisted of pedaling at a constant pace of 60 rpm against at 50% of the maximal aerobic power. The rest interval between the end of warm-up and the beginning of the anaerobic exercise was set at 5 min. Peak power (PP), mean power (MP), and the fatigue index (FI) were recorded. Likewise, heart rate, oral temperature (T), and rating of perceived exertion were registered at rest, at the end of the WU and just after the Wingate test. The ANOVA’s showed no main effect of the rest interval on PP, MP, FI, and T parameters. However, significant interactions (WU duration × time-of-day and recovery condition × WU duration) were recorded on both PP and MP parameters. PP and MP were higher in the afternoon compared to the morning with gains of 4.4 and 3.6%, respectively. In the morning sessions, the WU₁₅ allows better improvement of muscular power, with either 0- or 5-min pre-exercise rest interval. However, in the afternoon sessions, both WU₁₅ and WU₅ durations allow better improvement of 30-s Wingate cycling performance in, respectively, WR and NR conditions. Therefore, athletes and coaches, as well as researchers, interested in high-intensity cycling exercise, should take into account the rest interval, the time-of-day, and the duration of warm-up when practicing, assessing, or interpreting data related to powerful lower limbs’ muscles contractions activities.     

Does larder-hoarding affect the condition of chicks in urban kestrels?

Hoarding by urban kestrels and its subsequent exploitation significantly increases the frequency and regularity of feeding during the early stage of the nestling period. Twelve kestrels’ nests situated in various part of the city were chosen to test whether hoarding could affect the chicks’ condition. Four nests (with 22 nestlings) were provided with food — one dead mouse per chick per day (F group) and 8 (43 nestlings) were used as a control group (NF). Nestlings were weighed daily, and the length of their tarsus was also measured when the oldest chick in the nest was 11 days old. 50% of the NF nests experienced a decrease in the number of nestlings but no nestlings were lost in any of the F nests. However, no significant differences were found between the groups either in body mass or tarsus length. A possible reason was the behaviour of the adults which could be interpreted as the regulation of the frequency of prey delivery depending on its presence or absence in the nest.