M. H. Hansell

USING ARTIFICIAL NESTS TO TEST IMPORTANCE OF NESTING MATERIAL AND NEST SHELTER FOR INCUBATION ENERGETICS

Abstract Incubation is an energetically demanding process for parents, in part because of the thermodynamic costs of maintaining egg temperature. One might predict that aspects of nest construction—in particular, the thermodynamic properties of the nesting material and the degree to which the nest provides shelter from the wind—would have important effects on thermodynamic costs. However, little is known about the relative importance of those factors. Here, we investigate egg cooling rates in several commonly used nesting materials and in various wind speeds and examine the effect on those rates of wetting the materials. Nesting materials differ greatly in their insulating properties; feather down is the best insulator, and grass the worst. When the materials are wet, eggs cool much more rapidly, differences between materials tend to diminish, and down becomes the worst insulator. Hence, there may be significant selection pressure to choose particular nesting materials, but materials may be better or worse according to the situation of the nest. Increasing wind speed also has profound effects on egg cooling rates, even at the low speeds tested here, which implies strong selection pressure to locate and construct nests that minimize wind speed at the egg surface. Our results suggest that nest construction may have an important bearing on the subsequent costs of reproduction, and that important trade-offs may exist between nest construction for reduced thermodynamic costs, and other costs and benefits of nest-building and reproduction.

The ecological impact of animal nests and burrows

Nest building and burrow construction have costs. These costs are not well known but some attempts have been made to measure them either directly as energy and time consumed, or indirectly as fitness changes. Calculation of the energetic cost of web construction in the spider Araneus diadematus is an example of the former approach (Peakall & Witt 1976), and the cost of nest construction in the Eastern Phoebe (Sayornis phoebe) measured as clutch reduction compared with nest reuse (Weeks 1978), is an example of the latter. In some instances at least it can be seen that the result of these building efforts is a direct transfer of function from some other system to the artefact through evolution; for example, McNab (1966) showed that naked molerats (Heterocephalus glaber) which live permanently in the stable temperature of their burrow system had almost completely lost their power of physiological thermoregulation. Nests and burrows can also reduce the biological hazards of the external environment; for example, the paper carton nest of the tropical polistine wasp Nectarinella championi is surrounded by a field of hairs capped with sticky droplets apparently to repel ants (Schremmer 1977). The purpose of this paper is to present the argument that by their nature nests and burrows can come to exert important influences upon certain habitats and a number of different ways in which they do this can be identified (Fig. 1). These have implications for the understanding of social evolution, species diversity and habitat stability which deserve greater attention.

Developmental trade–offs in caddis flies: increased investment in larval defence alters adult resource allocation

Developmental trade–offs in resource allocation across life–history stages and between different body parts are predicted by life–history theories. However, there is very little empirical evidence that these occur. We investigated these trade–offs in caddis flies by experimentally manipulating larval case construction and thereby silk expenditure. Case building diverts protein resources away from larval stores, which are of major importance to adult development in species with little or no adult feeding. We induced fifth–instar Odontocerum albicorne to build new cases and examined the consequences for the morphology of the resulting adults. Rebuilding did not alter larval food consumption or the date of entering pupation, but shortened the duration of the pupal period. Adults that had been induced to expend more silk as larvae had lighter thoraces and smaller wings than the controls, but their abdomens did not differ significantly in mass or nitrogen content. These results suggest a trade–off between larval silk production and the pattern of resource allocation within the adult. The maintenance of the abdomen is likely to preserve reproductive potential, while the reduction in thoracic and wing investment will have negative consequences for flight and associated activities, and possibly for adult longevity.

Developmental trade-offs and life histories: strategic allocation of resources in caddis flies

Resource allocation trade–offs during development are potentially very important in the evolution of organism morphology and life–history strategy. However, they have rarely been demonstrated empirically. To what extent the division of limited resources between growing organs is a consequence of particular developmental pathways or varies strategically in line with life–history predictions is unknown. It has been demonstrated in a number of holometabolous insects that altering the resources available at pupation changes the pattern of allocation to adult tissues, but this has not been examined in a life–history context. Using caddis flies (Trichoptera), we show here that the effect of depleted larval resources on the pattern of somatic and reproductive investment is not fixed but varies between species with different life–history patterns. In particular, we demonstrate that, in a long–lived species, thorax size is preserved, which contrasts with the pattern previously observed in a short–lived species. That the adult body can be differentially altered by the same resource depletion in the larvae demonstrates that the allocation of resources amongst body parts is not a consequence of fixed pathways during development. Rather, the allocation of resources during development can occur in a manner consistent with the minimization of the effects on adult fitness.

The Relationship Between Some Psychological Factors and their Effect on the Performance of Grid Questions and Word Association Tests

This paper reports: (i) the relationship between certain psychological factors (i.e. field dependence/field independence, convergence/divergence and working memory capacity); and (ii) the effect of these factors on the performance of the grid-type of questions and of word association tests in biological concepts.

Repeatability of nest morphology in African weaver birds

It is generally assumed that birds build nests according to a genetic ‘template’, little influenced by learning or memory. One way to confirm the role of genetics in nest building is to assess the repeatability of nest morphology with repeated nest attempts. Solitary weaver birds, which build multiple nests in a single breeding season, are a useful group with which to do this. Here we show that repeatability of nest morphology was low, but significant, in male Southern Masked weaver birds and not significant in the Village weavers. The larger bodied Village weavers built larger nests than did Southern Masked weavers, but body size did not explain variation in Southern Masked weaver nest dimensions. Nests built by the same male in both species got shorter and lighter as more nests were constructed. While these data demonstrate the potential for a genetic component of variation in nest building in solitary weavers, it is also clear that there remains plenty of scope in both of these species for experience to shape nest construction.

Elements of eusociality in colonies of Eustenogaster calyptodoma (Sakagami & Yoshikawa) (Stenogastrinae, Vespidae)

The wasp Eustenogaster calyptodoma is at the lower limit of social complexity with colonies predominantly of one or two females. Nevertheless, in this study there was a recognizable division of labour with the oldest female guarding the nest entrance while a younger female did most of the foraging for food. This division of labour was maintained in the absence of any obvious dominance relationship. There was a female-biased sex ratio which could enhance the advantage to a female of staying in the maternal nest; however, colonies may be monogynous or polygynous and degrees of relatedness close or remote. Cooperation between females may therefore result from kinship effects or mutual interest in protection of nest and brood. Within a week of emergence, a young female generally left the nest to found a colony either by building her own nest or by usurping one plus its brood from another wasp. Usurping brood appears to be a method of acquiring assistance quickly in the running of the colony. The most advantageous action for a female therefore appears to be to found her own nest by usurping. Females failing to found probably return to the maternal nest. Factors promoting nest leaving probably include diluted degrees of relatedness between colony members due to polygyny and nest usurping, as well as to unsatisfactory nest material.

Why are pitfall traps so rare in the natural world

Prey capture by trapping is uncommon taxonomically, and generally requires highly evolved cognitive powers (humans) or specialist self-secreted materials (for example, spiders and caddisfly larvae). The most notable exception to this is the conical traps dug by antlion larvae. The relative uncommonness (taxonomically and ecologically) of such pitfall traps has been described as an unexplained mystery in recent publications. Here we suggest some potential routes that might lead to resolution to this mystery. We argue that although such pitfall traps have numerous benefits and are relatively cheap and easy to construct, they may suffer two significant disadvantages relative to, for example, spiders’ webs. First, pitfall traps may require a quite specialist microhabitat. Second, antlion pitfall traps may only work to retain all but the smallest prey if the antlion is present at the bottom of the pit. Thus, antlion may be more functionally tied to their trap than spiders and (since traps are much more visually conspicuous than their owners) this may make them vulnerable to predators and parasitoids that cue on the traps. Both these hypothesised drawbacks are speculative in the absence of a strong body of data and so we discuss how both potential costs could be explored empirically.

The function of lichen flakes and white spider cocoons on the outer surface of birds' nests

The predictions from two hypotheses for the adaptive significance of the application of lichen flakes and white silk cocoons to the outer surface of bird nests are compared. The hypotheses are: (a) concealment by resemblance to the branches to which the nest is attached, and (b) concealment by light reflection to make the nest dissolve into the background beyond the site of attachment. The predictions are tested with evidence obtained from a sample of 42 Long-tailed Tit (Aegithalos caudatus) nests and 64 Blue-grey Gnatcatcher (Polyoptila caerulea) nests, and from examination of single nests of over 50 other species. Little evidence is found to support branch matching although this hypothesis may partly or wholly explain the external application of lichen to the nests of some species. The hypothesis of concealment by light reflection is supported by the data, in particular by the general absence of lichen on branches to which lichen-covered nests are attached and the substitution in some species of pieces ...

Structural communication grids: a valuable assessment and diagnostic tool for science teachers

Structural communication grids involve data being presented in the form of a numbered grid and students being asked to select appropriate boxes, and to put them into a logical sequence, in response to a set question. Use of these grids give an insight into sub-concepts and linkages between ideas held by students, so that a deep level of understanding can be assessed.