Canadian Journal of Zoology

We provide data to support the onset of spasms (OS) as the definitive end point for determining thermal tolerance with the critical thermal maximum (CTMax). We measured the CTMax of 610 animals in three vertebrate classes, Actinopterygii, Amphibia, and Reptilia. All showed a significantly lower mean loss of righting response (LRR) than OS. Statistical evaluation of the variability associated with the end points LRR and OS also showed that OS is a more precise measure of thermal tolerance. OS is a more meaningful end point than LRR because it more closely fits the original definition of the critical thermal maximum (R.B. Cowles and C.M. Bogert. 1944. Bull. Am. Mus. Nat. Hist. 83: 261–296) and occurs at temperatures required for physiological responses, such as heat-hardening and perhaps the production of some heat-shock proteins. The adoption of OS as a standard end point would allow valid comparisons of data from different studies and among taxa, an important consideration for comparative phylogenetic analyses. However, we suggest that LRR should also be measured for comparisons with data from earlier studies.

Standard oxygen consumption, as estimated by simultaneously measuring spontaneous activity and oxygen consumption, for five species of freshwater fishes, was measured in relation to weight and temperature. The fish studied were brown trout, Sulmo trutta; brook trout, Salvelinus fontinalis; common white sucker, Catostomus commersonii; brown bullhead, Ictalurus nebulosus; and carp, Cyprinus carpio. When expressed on a logarithmic grid, standard oxygen uptake increased linearly with weight for all species. The proportionate change in standard oxygen consumption for a given change in temperature appears to be independent of size within each species. The mean slope values of the regressions found for brown trout, brook trout, common white sucker, brown bullhead, and carp are 0.877, 1.052, 0.864, 0.925, and 0.894, respectively.The standard rates of oxygen consumption found in the present investigation are less in most cases than the lowest applicable values that could be found in the literature.Spontaneous activity, expressed in terms of average oxygen consumption over the standard rate, varied with temperature. Maximum spontaneous activity for a given species coincided roughly with its preferendum temperature.

Sponges interact with most other organisms in marine systems as competitors, symbionts, hosts of symbionts, consumers, and prey. Considerable creative energy has been required to study and describe the amazing variety of sponge interactions, as sponges can hide symbionts deep inside, rapidly regenerate wounds from grazers, carry on important associations with unculturable microscopic organisms, and otherwise foil attempts to determine how they are interacting with other organisms. This review of sponge interactions covers (i) competition among sponge species, and between sponges and other sessile organisms; (ii) predation on sponges by sponge specialists and by opportunistic sponge feeders, and aspects of predation such as the importance of nutritional quality, trade-offs between growth and defense against predators, biogeographic patterns in predation, and the advantages of various techniques for studying predation; and (iii) symbiotic associations of sponges with a variety of organisms representing all types of life, and with results ranging from parasitism and disease to mutual benefit. A hint that some generalizations about ecological interactions of sponges may be possible is just becoming evident, as accumulating data appear to show taxonomic and geographic patterns; however, it is also clear that surprises will continue to emerge from every probing new study.

Two morphological forms of three-spined stickleback (Gasterosteus) coexist in Enos Lake near Nanoose Bay, Vancouver Island. For convenience, the two forms are referred to as "benthics" and "limnetics." Morphological and biochemical characteristics of the two forms were examined and artificial hybrids (F₁ and F₂) reared in the laboratory. The two forms differ in male nuptial colour, body shape, and gill raker architecture. These differences are inherited and have remained stable for several generations. Benthics and limnetics also differ in allele frequencies at three loci (Mdh-3, Ck, and Pgm). At one of these loci (Mdh-3) the limnetic form is polymorphic and the benthic form is fixed. Since the two forms maintain themselves as discrete entities and there is no evidence of gene flow, they are considered separate biological species. It is not certain that either of these species is Gasterosteus aculeatus. Similar species pairs exist in other lakes in the Strait of Georgia region but, at present, their relationship to the species pair in Enos Lake is unknown.

The carbon-isotope composition of hair and feces offers a glimpse into the diets of mammalian herbivores. It is particularly useful for determining the relative consumption of browse and graze in tropical environments, as these foods have strongly divergent carbon-isotope compositions. Fecal δ¹³C values reflect the last few days consumption, whereas hair provides longer term dietary information. Previous studies have shown, however, that some fractionation occurs between dietary δ¹³C values and those of hair and feces. Accurate dietary reconstruction requires an understanding of these fractionations, but few controlled-feeding studies have been undertaken to investigate these fractionations in any mammalian taxa, fewer still in large mammalian herbivores. Here, we present data from the first study of carbon-isotope fractionation between diet, hair, and feces in multiple herbivore taxa. All taxa were fed pure alfalfa (Medicago sativa) diets for a minimum period of 6 months, at which point recently grown hair was shaved and analyzed for carbon isotopes. The mean observed diet–hair fractionation was +3.2‰, with a range of +2.7 to +3.5‰. We also examined diet–feces fractionation for herbivores on alfalfa and bermudagrass (Cynodon dactylon) feeds. The mean diet–feces fractionation for both diets was –0.8‰, with less fractionation for alfalfa (–0.6‰) than bermudagrass (–1.0‰). Fecal carbon turnover also varies greatly between taxa. When diets were switched, horse (Equus caballus) feces reflected the new diet within 60 h, but alpaca (Lama pacos) feces did not equilibrate with the new diet for nearly 200 h. Thus, fecal carbon isotopes provide far greater dietary resolution for hindgut-fermenting horses than foregut-fermenting alpacas.

One of the performance features that is generally considered crucial to increasing the potential prey spectrum of lizards is bite capacity. In this study we tested whether bite forces may serve as a basis for diet selection in two syntopically occurring lacertid lizards. We did so by measuring bite forces in vivo for a large sample of lizards of the species Podarcis muralis and Lacerta vivipara. To assess the ecological relevance of the bite forces, we tested the hardness of a number of natural prey items of both species. The results of our study support the predictions of biomechanical models of biting in lizards and indicate that both larger animals and larger headed ones bite harder. Surprisingly, head shape is an excellent predictor of bite performance in the species studied. Moreover, it is demonstrated that bite capacity is a potentially important ecological variable that could be used as a factor in explaining patterns of food-resource use, ontogenetic dietary shifts, and sexual dimorphism in diet.

The literature pertaining to the prevalence of avian hematozoa in North America, north of Mexico, together with unpublished records from the files of the International Reference Centre for Avian Malaria Parasites, have been collated and analyzed with respect to the distribution of parasite genera by region, host family, and vertical stratification of nesting sites. The blood parasites of 57 026 birds of 388 species (representing 55 families) breeding in North America are the basis of this analysis. A total of 21 048 (36.9%) birds harbored one or more species of Haemoproteus (19.5%), Leucocytozoon (17.7%), Trypanosoma (3.9%), Plasmodium (3.8%), microfilariae (3.1%), and Haemogregarina/Lankesterella (0.6%). The continent was arbitrarily divided into seven regions along a topographic basis. Overall hematozoan prevalence varied markedly from region to region, as did the relative frequencies of the different genera. Overall hematozoan prevalence also varied markedly from avian family to family, as did the relative frequencies of the different genera. Nine families had prevalences of 50% or more, while 16 families had prevalences of 5% or less; sea- and shore-birds were nearly hematozoan-free. Prevalence of blood parasites is correlated with the vertical stratification of nesting sites when considered on a localized geographic basis but no correlation exists when the results are pooled from the continent.

Playback of recorded songs of white-throated sparrows (Zonotrichia albicollis) to territorial males elicited a stronger response to songs of strangers than to songs of territorial neighbors. Responses to a bird's own song were intermediate. All test songs were played on the territorial boundary adjacent to the neighbor used in the experiment. Peak of response by song occurred in the 1st min after cessation of playback.Two sets of experiments, 3 weeks apart, showed waning of response to neighbors' songs, but no change in response to strangers' songs. This waning progressed steadily over a 6-week period. No decrement was observed when four periods of playback of a neighbor's song were presented within 1 h. Response to a neighbor's song within a 1-h sequence was independent of whether the preceding playback was of a stranger or neighbor. This indicated that discrimination occurred after only one or two renditions of a song.The mechanism of differential response is interpreted as habituation to neighbors' songs. Adaptiveness of this behavior is discussed.

The last comprehensive reviews of ecology and natural history of ascidians were included in the excellent 1971 publication by Millar on the biology of ascidians and the 1991 treatise on New Caledonia ascidians by Monniot, Monniot, and Laboute. Several hundred papers have been published since that time, greatly expanding our knowledge of environmental tolerances and responses to increasing levels of anthropogenically derived toxins in marine waters, energetics and feeding strategies, predator–prey relationships, competition both intra- and inter-specific that include many studies of self–nonself recognition in colonial species, modes and environmental regulation of reproduction and development, symbionts, natural-product chemistry as antifouling and antipredator defenses, and dispersal mechanisms. The relatively new field of molecular genetics is revealing the presence of cryptic species and is helping to determine the origin of anthropogenically transported individuals, an important and growing problem that affects natural ecological relationships in marine communities worldwide. We are learning more about the difficult-to-study abyssal and Antarctic species. There have been great advances in our understanding of the importance in open-ocean food webs of the planktonic Appendicularia and Thaliacea. Also included in this review is a brief discussion of recent work on the Cephalochordata and Hemichordata.

Bees and angiosperms have shared a long and intertwined evolutionary history and their interactions have resulted in remarkable adaptations. Yet, at a time when the “pollination crisis” is of major concern as natural populations of both wild and honey bees ( Apis mellifera L., 1758) face alarming decline rates at a worldwide scale, there are important gaps in our understanding of the ecology and evolution of bee–flower interactions. In this review, we summarize and discuss the current knowledge about the role of floral chemistry versus other communication channels in bee-pollinated flowering plants, both at the macro- and micro-evolutionary levels, and across the specialization–generalization gradient. The available data illustrate that floral scents and floral chemistry have been largely overlooked in bee–flower interactions, and that pollination studies integrating these components along with pollinator behaviour in a phylogenetic context will help gain considerable insights into the sensory ecology and the evolution of bees and their associated flowering plants.