The Parisian comparative anatomist Claude Perrault, dissecting an Indian giant tortoise in 1676, was the first to observe that the urinary bladder is of an extraordinary size in terrestrial tortoises. In 1799, the English comparative physiologist Robert Townson suggested that the bladder functioned as a water reservoir, as he had shown previously for frogs and toads. However, these observations went unnoticed in subsequent reports on tortoise water economy that were made by travellers and naturalists visiting the Galapagos Archipelago and marvelling over the huge numbers of giant tortoises that inhabited these desert-like islands. The first such report was by an American naval officer, David Porter, who was a privateer in the 1812–15 war with England. In his journal he referred to the constant supply of water which the Galapagos tortoises carried with them. References to the location in the body, as well as the amounts and quality of the water stored, were, however, contradictory.

The confusion concerning the anatomical identity of the water reservoir in the Galapagos tortoise, Geochelone elephantopus, persisted throughout the nineteenth century, and continued when studies of tortoise water economy and drinking behaviour in arid environments were taken up independently in the desert tortoise, Gopherus agassizii, which inhabits the desert regions in the south-western United States. In 1881 Cox found large sacs filled with clear water under the carapace, but it was half a century later that these sacs were identified as the large bilobed bladder; references to specific water sacs continued to appear in the literature until the 1960s.

Since 1970, information on the water economy of desert tortoises has been obtained from extensive field studies. Rates of disappearance of tritiated water injected into the body have shown that during the drought periods of the summer, water turnover (intake) rates do not differ from the rates of metabolic water production. Under these conditions urine is not voided, but is stored in the large bladder. During a drought period the bladder urine increases from initially low osmolality finally to reach isosmolality with the blood plasma. Soluble K+ is the major cation of the urine, but large amounts of K+ are also present as precipitated urates. During a drought period the body is in negative water balance, but despite substantial losses of total body water, the plasma concentrations of Na+ and Cl− can remain constant for many months, indicating regulation of the extracellular fluid and water content of the body tissues by reabsorption of water from the urinary bladder. The bladder thus acts both as a store for nitrogenous waste and K+ and as a water reservoir during droughts. Following rain showers, there is a sharp decline in tritium activity correlated with copious drinking from temporary pools of rain water. The old bladder urine is voided and most of the water drunk is stored as a highly dilute urine.

In 1676 Perrault observed that in a freshwater turtle, Emys orbicularis, but not in the giant tortoise, two other bladders opened into the cloaca. By the mid-twentieth century it had been established that these cloacal bladders typically were restricted to species of chelonians that led a semi-terrestrial or semi-aquatic life. The function of the bladders has been debated since Townson observed in 1799 that dehydrated freshwater turtles took up water by anal drinking, suggesting that anal drinking served in the water economy of semi-terrestrial turtles. Since then, the bladders have been ascribed hydrostatic and respiratory functions, but the recent literature mostly argues for a respiratory function. The possible role of the cloacal bladders as a water reservoir in amphibious turtles is still open.

Terrestrial amphibians and tortoises are unique among vertebrates in possessing large urinary bladders that may function as water reservoirs in dry environments. This function depends upon copious water intake when water becomes available combined with discontinued voiding of urine in the absence of water. Adaptation to terrestrial habitats in ureotelic amphibians is correlated with tolerance of high urea concentrations in the body fluids. In arid-zone tortoises and uricotelic tree frogs, nitrogenous waste products are precipitated in the bladder, which functions as the main sink. Renewed contact with water releases drinking behaviour and voiding of the bladder urine until the accumulated excretory products are eliminated from the body and/or bladder, preparing the organism for re-exposure to arid conditions.

Birds evolved from and are phylogenetically recognized as members of the theropod dinosaurs; their first known member is the Late Jurassic Archaeopteryx, now represented by seven skeletons and a feather, and their closest known non-avian relatives are the dromaeosaurid theropods such as Deinonychus. Bird flight is widely thought to have evolved from the trees down, but Archaeopteryx and its outgroups show no obvious arboreal or tree-climbing characters, and its wing planform and wing loading do not resemble those of gliders. The ancestors of birds were bipedal, terrestrial, agile, cursorial and carnivorous or omnivorous. Apart from a perching foot and some skeletal fusions, a great many characters that are usually considered ‘avian’ (e.g. the furcula, the elongated forearm, the laterally flexing wrist and apparently feathers) evolved in non-avian theropods for reasons unrelated to birds or to flight. Soon after Archaeopteryx, avian features such as the pygostyle, fusion of the carpometacarpus, and elongated curved pedal claws with a reversed, fully descended and opposable hallux, indicate improved flying ability and arboreal habits. In the further evolution of birds, characters related to the flight apparatus phylogenetically preceded those related to the rest of the skeleton and skull. Mesozoic birds are more diverse and numerous than thought previously and the most diverse known group of Cretaceous birds, the Enantiornithes, was not even recognized until 1981. The vast majority of Mesozoic bird groups have no Tertiary records: Enantiornithes, Hesperornithiformes, Ichthyornithiformes and several other lineages disappeared by the end of the Cretaceous. By that time, a few Linnean ‘Orders’ of extant birds had appeared, but none of these taxa belongs to extant ‘families’, and it is not until the Paleocene or (in most cases) the Eocene that the majority of extant bird ‘Orders’ are known in the fossil record. There is no evidence for a major or mass extinction of birds at the end of the Cretaceous, nor for a sudden ‘bottleneck’ in diversity that fostered the early Tertiary origination of living bird ‘Orders’.

A revised six-kingdom system of life is presented, down to the level of infraphylum. As in my 1983 system Bacteria are treated as a single kingdom, and eukaryotes are divided into only five kingdoms: Protozoa, Animalia, Fungi, Plantae and Chromista. Intermediate high level categories (superkingdom, subkingdom, branch, infrakingdom, superphylum, subphylum and infraphylum) are extensively used to avoid splitting organisms into an excessive number of kingdoms and phyla (60 only being recognized). The two ‘zoological’ kingdoms, Protozoa and Animalia, are subject to the International Code of Zoological Nomenclature, the kingdom Bacteria to the International Code of Bacteriological Nomenclature, and the three ‘botanical’ kingdoms (Plantae, Fungi, Chromista) to the International Code of Botanical Nomenclature. Circumscriptions of the kingdoms Bacteria and Plantae remain unchanged since Cavalier-Smith (1981). The kingdom Fungi is expanded by adding Microsporidia, because of protein sequence evidence that these amitochondrial intracellular parasites are related to conventional Fungi, not Protozoa. Fungi are subdivided into four phyla and 20 classes; fungal classification at the rank of subclass and above is comprehensively revised. The kingdoms Protozoa and Animalia are modified in the light of molecular phylogenetic evidence that Myxozoa are actually Animalia, not Protozoa, and that mesozoans are related to bilaterian animals. Animalia are divided into four subkingdoms: Radiata (phyla Porifera, Cnidaria, Placozoa, Ctenophora), Myxozoa, Mesozoa and Bilateria (bilateral animals: all other phyla). Several new higher level groupings are made in the animal kingdom including three new phyla: Acanthognatha (rotifers, acanthocephalans, gastrotrichs, gnathostomulids), Brachiozoa (brachiopods and phoronids) and Lobopoda (onychophorans and tardigrades), so only 23 animal phyla are recognized. Archezoa, here restricted to the phyla Metamonada and Trichozoa, are treated as a subkingdom within Protozoa, as in my 1983 six-kingdom system, not as a separate kingdom. The recently revised phylum Rhizopoda is modified further by adding more flagellates and removing some ‘rhizopods’ and is therefore renamed Cercozoa. The number of protozoan phyla is reduced by grouping Mycetozoa and Archamoebae (both now infraphyla) as a new subphylum Conosa within the phylum Amoebozoa alongside the subphylum Lobosa, which now includes both the traditional aerobic lobosean amoebae and Multicilia. Haplosporidia and the (formerly microsporidian) metchnikovellids are now both placed within the phylum Sporozoa. These changes make a total of only 13 currently recognized protozoan phyla, which are grouped into two subkingdoms: Archezoa and Neozoa; the latter is modified in circumscription by adding the Discicristata, a new infrakingdom comprising the phyla Percolozoa and Euglenozoa). These changes are discussed in relation to the principles of megasystematics, here defined as systematics that concentrates on the higher levels of classes, phyla, and kingdoms. These principles also make it desirable to rank Archaebacteria as an infrakingdom of the kingdom Bacteria, not as a separate kingdom. Archaebacteria are grouped with the infrakingdom Posibacteria to form a new subkingdom, Unibacteria, comprising all bacteria bounded by a single membrane. The bacterial subkingdom Negibacteria, with separate cytoplasmic and outer membranes, is subdivided into two infrakingdoms: Lipobacteria, which lack lipopolysaccharide and have only phospholipids in the outer membrane, and Glycobacteria, with lipopolysaccharides in the outer leaflet of the outer membrane and phospholipids in its inner leaflet. This primary grouping of the 10 bacterial phyla into subkingdoms is based on the number of cell-envelope membranes, whilst their subdivision into infrakingdoms emphasises their membrane chemistry; definition of the negibacterial phyla, five at least partly photosynthetic, relies chiefly on photosynthetic mechanism and cell-envelope structure and chemistry corroborated by ribosomal RNA phylogeny. The kingdoms Protozoa and Chromista are slightly changed in circumscription by transferring subphylum Opalinata (classes Opalinea, Proteromonadea, Blastocystea cl. nov.) from Protozoa into infrakingdom Heterokonta of the kingdom Chromista. Opalinata are grouped with the subphylum Pseudofungi and the zooflagellate Developayella elegans (in a new subphylum Bigyromonada) to form a new botanical phylum (Bigyra) of heterotrophs with a double ciliary transitional helix, making it necessary to abandon the phylum name Opalozoa, which formerly included Opalinata. The loss of ciliary retronemes in Opalinata is attributed to their evolution of gut commensalism. The nature of the ancestral chromist is discussed in the light of recent phylogenetic evidence.

The ‘origin of larvae’ has been widely discussed over the years, almost invariably with the tacit understanding that larvae are secondary specializations of early stages in a holobenthic life cycle.

Considerations of the origin and early radiation of the metazoan phyla have led to the conclusion that the ancestral animal (=metazoan) was a holopelagic organism, and that pelago-benthic life cycles evolved when adult stages of holopelagic ancestors became benthic, thereby changing their life style, including their feeding biology.

The literature on the larval development and phylogeny of animal phyla is reviewed in an attempt to infer the ancestral life cycles of the major animal groups. The quite detailed understanding of larval evolution in some echinoderms indicates that ciliary filter-feeding was ancestral within the phylum, and that planktotrophy has been lost in many clades. Similarly, recent studies of the developmental biology of ascidians have demonstrated that a larval structure, such as the tail of the tadpole larva, can easily be lost, viz. through a change in only one gene. Conversely, the evolution of complex structures, such as the ciliary bands of trochophore larvae, must involve numerous genes and numerous adaptations.

The following steps of early metazoan evolution have been inferred from the review.

The holopelagic ancestor, blastaea, probably consisted mainly of choanocytes, which were the feeding organs of the organism. Sponges may have evolved when blastaea-like organisms settled and became reorganized with the choanocytes in collar chambers.

The eumetazoan ancestor was probably the gastraea, as suggested previously by Haeckel. It was holopelagic and digestion of captured particles took place in the archenteron. Cnidarians and ctenophores are living representatives of this type of organization. The cnidarians have become pelago-benthic with the addition of a sessile, adult polyp stage; the pelagic gastraea-like planula larva is retained in almost all major groups, but only anthozoans have feeding larvae.

Within the Bilateria, two major lines of evolution can be recognized: Protostomia and Deuterostomia. In protostomes, trochophores or similar types are found in most spiralian phyla; trochophore-like ciliary bands are found in some rotifers, whereas all other aschelminths lack ciliated larvae. It seems probable that the trochophore was the larval type of the ancestral, pelago-benthic spiralian and possible that it was ancestral in all protostomes. Most of the non-chordate deuterostome phyla have ciliary filter-feeding larvae of the dipleurula type, and this strongly indicates that the ancestral deuterostome had this type of larva.

Nuptial feeding encompasses any form of nutrient transfer from the male to the female during or directly after courtship and/or copulation. In insects, nuptial gifts may take the form of food captured or collected by the male, parts, or even the whole of the male's body, or glandular products of the male such as salivary secretions, external glandular secretions, the spermatophore and substances in the ejaculate. Over the past decade, there has been considerable debate over the current function of nuptial feeding in insects. This debate has centred on the issue of whether nuptial gifts function as paternal investment (i.e. function to increase the fitness and/or number of the gift-giving male's own offspring) or as mating effort (i.e. function to attract females, facilitate coupling, and/or to maximize ejaculate transfer), although the two hypotheses are not mutually exclusive. In the present article, evidence for the potential of nuptial gifts to function as either paternal investment, mating effort, or both is reviewed for each form of nuptial feeding in each insect taxon for which sufficient data are available. Empirical evidence suggests that many diverse forms of nuptial feeding in different insect taxa function, at least in part, as mating effort. For example, nuptial prey and salivary masses in the Mecoptera, regurgitated food in Drosophila (Diptera), hind-wing feeding in Cyphoderris (Orthoptera) and the secretion of the male's cephalic gland in Neopyrochroa (Coleoptera) and Zorotypus (Zoraptera) appear to function to entice females to copulate and/or to facilitate coupling. Nuptial prey and salivary masses in the Mecoptera also appear to function to maximize ejaculate transfer (which is also a form of mating effort), as do nuptial prey in Empis (Diptera), external glandular secretions in Oecanthus and Allonemobius (Orthoptera) and the spermatophylax in gryllids and tettigoniids (Orthoptera). Large spermatophores in, for example, the Lepidoptera and Coleoptera, also appear to be maintained by selection on the male to maximize ejaculate transfer and thereby counter the effects of sperm competition. In contrast to the large amount of evidence in support of the mating effort hypothesis, there is a relative lack of good evidence to support the paternal investment hypothesis. Certain studies have demonstrated an increase in the weight and/or number of eggs laid as a result of the receipt of larger gifts, or a greater number of gifts, in tettigoniids, gryllids, acridids, mantids, bruchid beetles, drosophilids and lepidopterans. However, virtually all of these studies (with the possible exception of studies of the spermatophylax in tettigoniids) have failed to control adequately for hormonal substances in the ejaculate that are known to affect female reproductive output. Furthermore, in at least four tettigoniids (but not in the case of two species), three lepidopterans, a drosophilid and probably also bruchid beetles and bittacids, evidence suggests that the male has a low probability of fertilising the eggs that stand to benefit from his nuptial gift nutrients. Therefore, the hypothesis that paternal investment might account for the function of nuptial gifts in general is not supported.

The Triassic reptile Euparkeria has been frequently given a pivotal position in interpretations of the evolution of archosaurs. Most recently, Welman (1995) has argued from braincase data that Euparkeria is more closely related to birds than are either theropod dinosaurs or crocodilians – a conclusion clearly at odds with the current orthodoxy. The braincase of a single specimen of Euparkeria is described in detail and compared with previous descriptions and with the braincases of other diapsids. Variations among the known specimens are documented. The homology of various braincase structures are reassessed in light of the study by Welman (1995). We argue that the braincase of Euparkeria has an undivided metotic fissure, an incompletely ossified medial wall of the otic capsule, a well-defined ‘semilunar depression’, and posteroventrally positioned foramina in the parabasisphenoid for the entrance of the cerebral branches of the internal carotid arteries. It lacks enclosure of the Eustachian system in bone, well-developed tympanic sinuses, or a well-defined recess for the lagena. A review of braincase morphology in extinct and extant diapsids suggests that braincase features of Euparkeria are largely plesiomorphic for Archosauria. The evolutionary relationships between Euparkeria and extant archosaurs (birds and crocodilians) are considered by reviewing braincase morphology in extant and extinct diapsids. No shared derived characters could be found that support the resolutions (crocodilians (Euparkeria+birds)) or (birds (Euparkeria+crocodilians)). Three derived characters shared by extant archosaurs support the resolution (Euparkeria (crocodilians+birds)), but only the presence of laterally positioned foramina in the parabasisphenoid for the entrance of the cerebral branches of the internal carotid arteries appears to represent strong evidence. The other two features are a degree of ossification (of the medial wall of the otic capsule) that exhibits some homoplasy among archosaurs, and an absence (of the ‘semilunar depression’), and therefore do not represent particularly robust hypotheses of homology. Our interpretation of the braincase of Euparkeria is fully congruent with the consensus among recent explicit phylogenetic analyses that this taxon is close to, but not a member of, the archosaur crown group. Birds and crocodilians share a number of other derived similarities (subdivided metotic fissure, elongated and tubular cochlear recess, enclosed Eustachian system, extensive tympanic sinuses, quadrate-prootic articulation) that are probably not homologous because of their absence in a number of non-avian dinosaurs and crocodilian-line crown-group archosaurs.

The use of video images in place of natural stimuli in animal behaviour experiments is reviewed. Unlike most other artificial means of stimulus presentation, video stimuli can depict complex moving objects such as other animals, preserving the temporal and spatial patterns of movement precisely as well as colour and sounds for repeated playback. Computer editing can give flexibility and control over all elements of the stimulus. A variety of limitations of video image presentation are also considered. Televisions and video monitors are designed with human vision in mind, and some non-human animals that differ in aspects of visual processing such as their colour vision, critical flicker-fusion threshold, perception of depth and visual acuity, may perceive video images differently to ourselves. The failure of video stimuli to interact with subjects can be a drawback for some studies. For video to be useful, it is important to confirm that the subject animal responds to the image in a comparable way to the real stimulus, and the criteria used to assess this are discussed. Finally, the contribution made by video studies to date in the understanding of animal visual responses is considered, and recommendations as to the future uses of video are made.

The range of environmental sex determination and sex changes throughout plant taxa from bryophytes and pteridophytes to spermatophytes is reviewed. Lability in sex expression occurs in many plant taxa but only in homosporous pteridophytes is labile sex the rule. Among angiosperms, labile sex appears to be more common among dioecious and monoecious plants than among hermaphrodites. However, hermaphrodites can control allocation to male and female functions by varying the relative emphasis on pollen and ovules. A majority of plants with labile sex expression are perennials, which indicates that flexibility in sex is more important for species with long life cycles. Environmental stress, caused by less-than-optimal light, nutrition, weather or water conditions, often favours maleness. The extreme lability in the sex expression of homosporous pteridophytes is suggested to be related primarily to the mating systems.

Current knowledge of frugivory and seed dispersal by vertebrates in the Oriental Region is summarized. Some degree of frugivory has been reported for many fish and reptile species, almost half the genera of non-marine mammals and more than 40% of bird genera in the region. Highly frugivorous species, for which fruit dominates the diet for at least part of the year, occur in at least two families of reptiles, 12 families of mammals and 17 families of birds. Predation on seeds in fleshy fruits is much less widespread taxonomically: the major seed predators are colobine monkeys and rodents among the mammals, and parrots, some pigeons, and finches among the birds. Most seeds in the Oriental Region, except near its northern margins, are dispersed by vertebrate families which are endemic to the region or to the Old World. Small fruits and large, soft fruits with many small seeds are consumed by a wide range of potential seed dispersal agents, including species which thrive in small forest fragments and degraded landscapes. Larger, bigger-seeded fruits are consumed by progressively fewer dispersers, and the largest depend on a few species of mammals and birds which are highly vulnerable to hunting, fragmentation and habitat loss.

The connection between development and evolution has become the focus of an increasing amount of research in recent years, and heterochrony has long been a key concept in this relation. Heterochrony is defined as evolutionary change in rates and timing of developmental processes; the dimension of time is therefore an essential part in studies of heterochrony. Over the past two decades, evolutionary biologists have used several methodological frameworks to analyse heterochrony, which differ substantially in the way they characterize evolutionary changes in ontogenies and in the resulting classification, although they mostly use the same terms. This review examines how these methods compare ancestral and descendant ontogenies, emphasizing their differences and the potential for contradictory results from analyses using different frameworks. One of the two principal methods uses a clock as a graphical display for comparisons of size, shape and age at a particular ontogenic stage, whereas the other characterizes a developmental process by its time of onset, rate, and time of cessation. The literature on human heterochrony provides particularly clear examples of how these differences produce apparent contradictions when applied to the same problem. Developmental biologists recently have extended the concept of heterochrony to the earliest stages of development and have applied it at the cellular and molecular scale. This extension brought considerations of developmental mechanisms and genetics into the study of heterochrony, which previously was based primarily on phenomenological characterizations of morphological change in ontogeny. Allometry is the pattern of covariation among several morphological traits or between measures of size and shape; unlike heterochrony, allometry does not deal with time explicitly. Two main approaches to the study of allometry are distinguished, which differ in the way they characterize organismal form. One approach defines shape as proportions among measurements, based on considerations of geometric similarity, whereas the other focuses on the covariation among measurements in ontogeny and evolution. Both are related conceptually and through the use of similar algebra. In addition, there are close connections between heterochrony and changes in allometric growth trajectories, although there is no one-to-one correspondence. These relationships and outline links between different analytical frameworks are discussed.

Although the uses and merits of terrestrial insects as indicators have been extensively discussed, there is a lack of clear definition, goal directedness and hypothesis testing in studies in the field. In an attempt to redress some of these issues and outline an approach for further studies, three categories of terrestrial insect indicators, corresponding to differences in their application, are proposed, i.e. environmental, ecological and biodiversity indicators. The procedures in terrestrial insect bioindicator studies should start with a clear definition of the study objectives and proposed use of the bioindicator, as well as with a consideration of the scale at which the study is to be carried out. Bioindication studies are conducted at a variety of spatial and temporal scales within the context of earth-system processes, but the objectives of the study will largely determine the scale at which it would be optimally conducted. There is a tendency for studies to be conducted below their space-time scaling functions, giving them apparent predictability. The selection of potential indicator taxa or groups is then based on a priori suitability criteria, the identification of predictive relationships between the indicator and environmental variables and, most importantly, the development and testing of hypotheses according to the correlative patterns found. Finally, recommendations for the use of the indicator in monitoring should be made. Although advocating rigorous, long-term protocols to identify indicators may presently be questionable in the face of the urgency with which conservation decisions have to be made, this approach is critical if bioindicators are to be used with any measurable degree of confidence.

We reviewed information on the demands of incubation to examine whether these could influence the optimal clutch size of birds. The results indicate that appreciable metabolic costs of incubation commonly exist, and that the incubation of enlarged clutches can impose penalties on birds. In 23 studies on 19 species, incubation metabolic rate (IMR) was not elevated above the metabolic rate of resting non-incubating birds (RMR), but contrary to the physiological predictions of King and others, IMR was greater than RMR in 15 studies on 15 species. Across species, IMR was substantially above basal metabolic rate (BMR), averaging 1.606×BMR. Of six studies on three species performed under thermo-neutral conditions, none found IMR to be in excess of RMR. IMRs measured exclusively within the thermo-neutral zone averaged only 1.08×BMR contrasting with the significantly higher figure of 1.72×BMR under wider conditions. 16 of 17 studies on procellariiforms found IMR below RMR, indicating a significant difference between this and other orders. We could find no other taxonomic, or ecological factors which had clear effects on IMR. Where clutch size was adjusted experimentally during incubation, larger clutches were associated with: significantly lower percentage hatching success in 11 of 19 studies; longer incubation periods in eight of ten studies; greater loss of adult body condition in two of five studies; and higher adult energy expenditure in eight of nine studies. Given that incubation does involve metabolic costs and given that the demands of incubation increase sufficiently with clutch size to affect breeding performance, we propose that the optimal clutch size of birds may in part by shaped by the number of eggs the parents can afford to incubate.

A description of the relationship between mean food intake rate (MFIR) and group size is important in assessing the adaptiveness of group living in animals. Several hypotheses argue that foraging in groups can be beneficial in terms of MFIR but an overall assessment of the evidence available thus far was lacking. I examined this relationship in birds using studies that provided a measure of MFIR in groups of different sizes and evaluated the effect of study design and food type. In addition, I noted some of the mechanisms thought to be responsible for changes in MFIR with group size and quantified the impact of the addition of individual foragers. The most common pattern of change in MFIR with group size was a monotonic increase. The different patterns of change in MFIR with group size occurred with similar frequencies in experimental and observational studies despite the fact that observational studies often lacked control for confounding factors. Increases in MFIR were more likely to be associated with seeds as a food type than with fish or invertebrates, and were least likely with carcasses. This finding was related to the ease with which individuals can use aggression to increase their share of resources that are more concentrated in space. Adjustments in vigilance levels and aggression, as well as more subtle changes in speed of search and handling time, were correlated with changes in MFIR with group size. Finally, the addition of three to four individuals appeared to be needed to double the MFIR of a solitary bird. The results suggest that foraging in avian groups is often associated with increased MFIRs and that several ecological factors, including food dispersion, influence the pattern of change with group size.

Allelopathy is an interference mechanism by which plants release chemicals which affect other plants; while it has often been proposed as a mechanism for influencing plant populations and communities, its acceptance by plant ecologists has been limited because of methodological problems as well as difficulties of relating the results of bioassays used for testing allelopathy to vegetation patterns in the field. Here we argue that the concept of allelopathy is more appropriately applied at the ecosystem-level, rather than the traditional population/community level of resolution. Firstly, we consider the wide ranging effects of secondary metabolites (widely regarded as allelochemicals) on organisms and processes which regulate ecosystem function, including herbivory, decomposition and nutrient mineralization. It is apparent that plants with allelopathic potential against other organisms induce net changes in ecosystem properties, which may in turn impact upon the plant community in the longer term. We then illustrate these concepts using two contrasting examples of how invasive plant species with allelopathic potential may alter ecosystem properties through the production of secondary metabolites, i.e. Carduus nutans (nodding thistle) in New Zealand pastures and Empetrum hermaphroditum (crowberry) in Swedish boreal forests. In both cases the production of secondary metabolites by the invasive species induces important effects on other organisms and key processes, which help determine how the ecosystem functions and ultimately the structure of the plant community. These examples help demonstrate that the concept of allelopathy is most effectively applied at the ecosystem-level of resolution, rather than at the population-level (i.e. plant-plant interference).

I analyse and summarize the empirical evidence in mammals supporting alternative benefits that individuals may accrue when committing nonparental infanticide. Nonparental infanticide may provide the perpetrator with nutritional benefits, increased access to limited resources, increased reproductive opportunities, or it may prevent misdirecting parental care to unrelated offspring. The possibility that infanticide is either a neutral or maladaptive behaviour also is considered. I devote the second half of this article to reviewing potential mechanisms that individuals may use to prevent infanticide. These counterstrategies include the early termination of pregnancy, direct aggression by the mother against intruders, the formation of coalitions for group defence, the avoidance of infanticidal conspecifics, female promiscuity, and territoriality. I evaluate the support for each benefit and counterstrategy across different groups of mammals and make suggestions for future research.