Temporal and spatial patterns in the emigrations of the army ant Dorylus (Anomma) molestus in the montane forest of Mt Kenya

Abstract.  1. The emigration behaviour of the army ant Dorylus ( Anomma ) molestus was studied in the montane forest of Mt Kenya. This species forages by massive swarm raids (mean width 10.3 m ± 4.6 m SD), which are assumed to have a strong negative impact on the densities of prey populations.
2. For non-reproductive colonies the stay duration in a nest is highly variable (median 17, range 3–111 days). This suggests that the frequency of emigrations is not dictated by a brood cycle as an underlying endogenous pattern generator.
3. Colony density is high (mean nearest neighbour's distance 82.1 m ± 29.4 m SD) and mean foraging range is 75.0 m, so encounters with neighbouring colonies occur frequently.
4. The straight line emigration distance is on average 92.7 m (± 29.7 SD). The emigration direction is random with respect to absolute bearing and also relative to the direction of the previous emigration. However, the emigration direction is influenced by the location of the nearest neighbour. Colonies typically emigrate directly away from their nearest neighbour.
5. Local food depletion is likely to be the ultimate cause for emigrations in this species, because emigration distance is larger than foraging range and colonies move away from their nearest neighbour. A small percentage of emigrations may be triggered by pangolin attacks on nests.
6. Contrary to the prediction of a recently developed mathematical model for epigaeic swarm-raiding Dorylus ( Anomma ) species, D.  ( A .)  molestus colonies do not engage in intraspecific battles. Possible reasons for the absence of fights between colonies despite apparently fierce intraspecific competition are discussed.     

Ellen Dissanayake’s Evolutionary Aesthetic

Dissanayake argues that art behaviors – which she characterizes first as patterns or syndromes of creation and response and later as rhythms and modes of mutuality – are universal, innate, old, and a source of intrinsic pleasure, these being hallmarks of biological adaptation. Art behaviors proved to enhance survival by reinforcing cooperation, interdependence, and community, and, hence, became selected for at the genetic level. Indeed, she claims that art is essential to the fullest realization of our human nature. I make three criticisms: Dissanayake’s theory cannot account adequately for differences in the aesthetic value of artworks; the connections drawn between art and reproductive success are too stretched to account for art's production, nature, and reception; indeed, art enters the picture only because it is so thinly characterized that it remains in doubt that her topic is art as we understand it.     

Excavation and architecture of Argentine ant nests

We used x-ray computed tomography to study the elaboration of nest structures in small sand-filled nest boxes by Argentine ant (Linepithema humile) colonies composed of 10, 100, and 1000 workers. The pattern of nest growth was consistent with a process of density-dependent stimulation of excavation, which subsided as nests grew and the density of digging stimuli declined. Thus, nest excavation would be auto-regulating, and final nest size should be adjusted to colony size. We found that excavation rates and final nest sizes increased with colony size, but were not tenfold greater in 1000-worker colonies than in 100-worker colonies. In the largest colonies, the internal surface area scaled allometrically with volume, so that more surface was obtained relative to volume excavated as the nest grew. Although the gross features of Argentine ant nests, such as total size, seem explicable by a simple, self-organized regulatory process, other features of the nest architecture will require further investigation. Received 3 March 2005; revised 26 April 2005; accepted 3 May 2005.     

Predictors of clutch predation of a globally significant avifauna in New Zealand's braided river ecosystems

Predation by introduced mammals is decimating New Zealand's indigenous fauna. Understanding factors that influence this process allows resources for predator control to be applied with maximum effect. This study examines how predation of a secondary prey species (a relatively common but declining native plover, the banded dotterel Charadrius bicinctus ) varied with reductions in abundance of a major prey source (rabbits), kill-trapping of predators, nest density and habitat complexity. Banded dotterels mostly nest in open braided riverbeds alongside a number of endemic threatened species. We measured the fate of 753 dotterel clutches exposed to predation by cats, ferrets and hedgehogs. We found key times and places of high predation risk. Immediately after widespread reduction in rabbit populations by rabbit haemorrhagic disease (RHD), clutch predation rates were almost as high (mean, 50%) as those recorded during past rabbit poisoning programmes (mean, 57%). Both rates were significantly higher than the mean predation rate of 22% without rabbit control, suggesting a shift in predator diet immediately after rabbit population declines. Unlike after rabbit poisoning, clutch predation rate remained high in the years after RHD. Other patterns observed included higher clutch predation rate where nest density was lower, suggesting that predation can potentially cause local extinction. Clutch predation was also higher along riverbed margins where vegetation was dense. There was equivocal evidence for an effect of predator kill-trapping on clutch predation rate. Management strategies that could potentially reduce clutch predation risks include focusing predator mitigation measures during periods of rabbit decline, maintaining them for more than one breeding season if the rabbit declines are widespread (e.g. RHD epidemics), and applying greater effort at sites with relatively low nest density and along riverbed margins where predator use is more frequent.     

人工释放苜蓿切叶蜂的营巢行为观察

苜蓿切叶蜂Megachile rotundata Fabricius是紫花苜蓿的理想授粉昆虫,国内外已广泛利用切叶蜂为紫花苜蓿授粉,因此,对切叶蜂的田间活动行为分析具有重要的实践指导意义。对苜蓿切叶蜂的田间营巢行为进行观测,结果表明:整个花期切叶蜂均十分活跃,放蜂的第4天开始适应环境,正常活动,7月8～22日,切叶蜂最为活跃,进入蜂巢的切叶蜂数最高时达426头/蜂巢,每日10:00～16:00为活动高峰。每日每块蜂巢的封孔数最多为14个,平均每个蜂室封闭巢孔的数量最多为185个。     

Effects of a low oxygen environment on parental effort and filial cannibalism in the male sand goby, Pomatoschistus minutus

In fish, brood cycling parental males sometimes eat some orall of their eggs, a behavior termed filial cannibalism. Wetested predictions of filial cannibalism models related to thecost of parental care in the male sand goby, Pomatoschistusminutus, by increasing the parental effort (fanning expenditure)through reduced levels of dissolved oxygen to 39% in an experimentalgroup, whereas a control group had fully saturated water. Malesshowed both full-clutch cannibalism and partial-clutch cannibalismin both treatments. Giving the males one to three females tospawn with, we found that small clutches were completely eatenmore often than were larger ones, whereas partial-clutch cannibalismwas not affected by clutch size. Although treatment did notaffect filial cannibalism, it did affect a male's energy statesuch that males in the low oxygen treatment lost more body fat,indicating a greater fanning effort. This shows that males inthe low oxygen treatment allocated more energy to the presentbrood, potentially at the expense of future reproductive success.Our study strongly suggests that filial cannibalism in malesand gobies represents a strategic life-history decision asan investment in future reproductive success, and is not triggeredby a proximate need for food necessary for the male's own survival.Furthermore, males in the low oxygen treatment built nests withlarger entrances, and were less likely to rebuild their nestsafter destruction. Presumably, this makes fanning easier butthe nest more vulnerable to predators, suggesting a trade-offbetween fanning and nest defense.     

The Effect of Rain Forest Canopy Architecture on the Distribution of Epiphytic Ferns (Asplenium spp.) in Sabah, Malaysia

Epiphytic plants are a dominant component of the rain forest canopy biota. They represent a significant proportion of canopy plant biomass and diversity, play a key role in nutrient cycling, and support highly abundant and diverse animal communities. Understanding the factors affecting their distribution in this three-dimensional habitat is consequently of great importance, not least because they may be particularly vulnerable to climate change and habitat conversion. Here we investigate how canopy architecture affects the distribution of two species of bird's nest fern ( Asplenium spp.) in pristine rain forest. Both species were found at high abundances ( Asplenium phyllitidis : 136/ha, SE ± 31.6, Asplenium nidus : 44/ha, SE ± 9.2) and their distributions were differentially affected by canopy architecture. Asplenium phyllitidis was found only at heights < 30 m in areas with a thicker lower canopy layer. Asplenium nidus was found at all heights in the canopy and was associated with emergent trees and areas with an open understory. Larger A. phyllitidis were found higher in the canopy while larger A. nidus were found on trunks and branches with a wider diameter. Asplenium nidus seems adapted to withstand the hot dry conditions in the upper canopy and in gaps, and its size is consequently limited only by the size of its support. Asplenium phyllitidis is dominant in areas that are cooler and damper, and so the growth rate of individuals may be limited by light levels. We discuss possible implications of this partitioning for epiphyte communities in the face of climate change and habitat conversion.
     

Reproductive success of Tree Pipits Anthus trivialis in relation to habitat selection in conifer plantations

Aspects of the reproductive success of Tree Pipits Anthus trivialis were examined in relation to broad‐scale habitat and nest‐site selection in Thetford Forest, a coniferous plantation forest in eastern England. Three habitat classes were defined corresponding to previously reported densities of Tree Pipits: clearfell and recently planted stands (habitat class A: low density), stands 2–5 years old (B: high density) and stands 6 years or older (C: low density). The preference for 2–5‐year‐old stands indicated by higher densities was supported by the timing of territory settlement. Tree Pipits also showed distinct preferences for nest‐site characteristics that were relatively consistent across habitat classes and throughout the breeding season. At the ‘habitat scale’, results were consistent with the predictions of the ideal despotic distribution model. First clutches were laid significantly earlier in the preferred habitat class B. Overall nesting success (i.e. the proportion of nests producing fledglings), but not clutch size, also varied between habitats, being greater in habitat classes B and C than in habitat class A. The variation in overall nesting success between habitats was primarily driven by low nest survival rates during the laying/incubation period in clearfell and recently planted stands. Nest survival rates during the nestling period were lower in the preferred 2–5‐year‐old (and older) stands and declined over the course of the study. Preferences for nest‐site characteristics (at least for those that were measured) provided no apparent benefit to nest survival rates. Overall nesting success thus appeared to be determined at the habitat scale, perhaps because the broad differences in cover between habitats affected the likelihood of nest predation (the main cause of nest failure). It is suggested that the very low nesting success experienced by Tree Pipits in clearfell and new stands may be one factor in the species’ relative avoidance of this habitat and preference for 2–5‐year‐old stands.     

Maternal investment in relation to sex ratio and offspring number in a small mammal – a case for Trivers and Willard theory?

1.  Optimal parental sex allocation depends on the balance between the costs of investing into sons vs. daughters and the benefits calculated as fitness returns. The outcome of this equation varies with the life history of the species, as well as the state of the individual and the quality of the environment.
2.  We studied maternal allocation and subsequent fecundity costs of bank voles, Myodes glareolus , by manipulating both the postnatal sex ratio (all-male/all-female litters) and the quality of rearing environment (through manipulation of litter size by −2/+2 pups) of their offspring in a laboratory setting.
3.  We found that mothers clearly biased their allocation to female rather than male offspring regardless of their own body condition. Male pups had a significantly lower growth rate than female pups, so that at weaning, males from enlarged litters were the smallest. Mothers produced more milk for female litters and also defended them more intensively than male offspring.
4.  The results agree with the predictions based on the bank vole life history: there will be selection for greater investment in daughters rather than sons, as a larger size seems to be more influencial for female reproductive success in this species. Our finding could be a general rule in highly polygynous, but weakly dimorphic small mammals where females are territorial.
5.  The results disagree with the narrow sense Trivers & Willard hypothesis, which states that in polygynous mammals that show higher variation in male than in female reproductive success, high-quality mothers are expected to invest more in sons than in daughters.     

The Effects of Artificial Beach Nourishment on Marine Turtles: Differences between Loggerhead and Green Turtles

Marine turtle reproductive success is correlated with the stability and quality of the nesting environment. Female marine turtles show fidelity to nesting beaches, making artificial beach nourishment practices directly relevant to their recovery. We evaluated the impacts of artificial beach nourishment on Loggerhead ( Caretta caretta ) and Green turtles ( Chelonia mydas ) between artificially nourished and nonnourished beaches. We observed reduced nesting success (ratio of nesting emergences to emergences not resulting in nest deposition) for both species. This negative effect lasted for one season in Loggerheads and for at least one season in Green turtles. Physical attributes of the fill sand did not impede nesting attempts. We argue that the decrease in nesting success resulted from an altered beach profile not favorable for nest deposition, which subsequently improved in later seasons as the beach equilibrated to a more natural slope. We observed a 52.2% decrease in reproductive output (hatchlings km⁻¹ yr⁻¹) for Loggerheads one year postnourishment, with a 44.1% increase observed the two seasons postnourishment. In Green turtles, a 0.8% reduction was observed the first season postnourishment, despite a 13% increase in the nonnourished area. The reduction in reproductive output in both cases was primarily a consequence of decreased nesting success, lowering nest numbers. These results reveal stronger negative effects of beach nourishment on Loggerheads compared to Green turtles and the importance of minimizing excessive nonnesting emergences associated with artificial beach nourishment. Nourished areas also experienced more than 600% increase in the number of Loggerhead hatchlings disoriented by artificial lighting over two years postnourishment.