Carnivore olfactory bulb size: allometry, phylogeny and ecology

Olfactory bulb size was measured in 146 species of Carnivora in order to examine whether recently observed functional patterns for overall brain size were similar for component parts of the brain. Comparative measures were analysed in relation to various allometric characters (body, brain and skull size), phylogeny, behaviour and ecology. Olfactory bulbs are significantly and positively correlated with all allometric variables, but indices of skull size correlate slightly more closely than other variables. This probably relates to functional aspects of skull size, facial proportions, and anterior elements of the brain. Phylogenetic associations were examined by two comparative methods: the method of independent contrasts and phylogenetic autoregression. Both revealed similar phylogenetic correlation at generic and familial levels. Using calculated values from either method, relative olfactory bulb size only correlates with zonation among seven behavioural and ecological variables; aquatic otters have smaller bulb sizes than carnivores of other zonal types. This agrees with discussion about the diminution of olfactory communication in aquatic environments. Also, olfactory bulb size correlates with home range size, which is consistent with a recent model on the use of olfaction for foraging in designated home ranges. Generally, comparative differences in olfactory bulb size in carnivores do not associate with functional variables found in other comparative studies. Nevertheless, future analyses of specific brain components in mammals may be more useful than overall brain size for testing evolutionary hypotheses of mammalian brain size.     

Context‐dependent fruit–frugivore interactions: partner identities and spatio‐temporal variations

Fruit–frugivore interactions are crucial for the dynamics and regeneration of most forested ecosystems. Still, we lack an understanding of the potential variation in the sign and strength of such interactions in relation to variations in the spatial and temporal ecological context. Here, we evaluated spatial (three sites) and temporal (two fruiting seasons) local variation in the sign (seed predation versus dispersal) and strength (frequency and quantity) of the interactions among six frugivorous mammals and a community of Mediterranean fleshy‐fruited shrubs. We examined mammal faecal samples and quantified frequency of seed occurrence, number of seeds per faecal sample, seed species diversity and quality of seed treatment (i.e. percentage of undamaged seeds). The frequency of seed occurrence and number of seeds per faecal sample strongly varied among dispersers, sites, seasons and fruit species. For instance, fox Vulpes vulpes faeces showed between 6 and 40 times more seeds than wild boar Sus scrofa faeces in seasons or sites in which Rubus and Juniperus seeds were dominant. However, in seasons or sites dominated by Corema seeds, wild boar faeces contained up to seven times more seeds than fox faeces. Mammalian carnivores (fox and badger, Meles meles) treated seeds gently, acting mostly as dispersers, whereas deer (Cervus elaphus and Dama dama) acted mainly as seed predators. Interestingly, rabbit Oryctolagus cuniculus acted as either mostly seed disperser or seed predator depending on the plant species. Our results indicated that the sign of fruit–frugivore interactions depended mainly on the identity of the partners. For a particular fruit–frugivore pair, however, our surrogate of interaction strength largely varied with the spatio‐temporal context (year and habitat), leading to a low specificity across the seed–frugivore network. The high spatio‐temporal variability of seed dispersal (in quantity, quality and seed diversity) by different frugivores would confer resilience against unpredictable environmental conditions, such as those typical of Mediterranean ecosystems.     

Leaf size, sapling allometry, and Corner's rules: phylogeny and correlated evolution in maples (Acer)

We studied the evolution of leaf size, sapling canopy allometry, and related traits in 17 Acer species growing in the understory of temperate deciduous forests, using parsimony methods, randomization tests, and independent contrasts calculated on idena phylogeny inferred from nuclear ribosomal internal transcribed spacer (ITS) sequences. Bivariate correlations and multivariate analyses indicated two independent suites of coevolving traits, and the results were robust over a range of alternative phylogenies. The first suite consisted of strong positive correlations among twig thickness, leaf size, inflorescence length, and branch spacing (Corner's rules). Seed size and mature height were also weakly corre- lated with these traits. The second suite reflected aspects of sapling crown allometry, including crown size, stem diameter, and total leaf area, which appear to be related to shade tolerance. There was a weak negative correlation between sapling crown size and mavegetative ture height, but no correlation with leaf or seed size. Most correlattion were similar in magnitude for ahistorical and independent contrasts analyses, and discrepancies between these two measures were greater in traits with lower levels of convergent evolution. The evolutionary correlations among twig, leaf, seed, inflorescence, and canopy dimensions emphasize the need for integrated theories of evolution and function of these disparate traits.     

Pine invasions in the southern hemisphere: modelling interactions between organism,environment and disturbance

Current theories of plant invasion have been criticized for their limited heuristic and predictive value. We explore the heuristic and predictive potential of a model which explicitly simulates the mechanisms of plant invasion. The model, a spatially-explicit individual-based simulation, is applied to the invasion of pine trees (Pinus spp.; Pinaceae) in three vegetation types in the southern hemisphere. The model simulates factors which have been invoked as major determinants of invasive success: plant traits, environmental features and disturbance level. Results show that interactions between these determinants of invasive success are at least as important as the main effects. The complexity of invasions has promoted the belief that many factors must be invoked to explain invasions. This study shows that by incorporating interactions and mechanisms into our models we can potentially reduce the number of factors needed to predict plant invasions. The importance of interactions, however, means that predictions about invasions must be context-specific. The search for all-encompassing rules for invasions is therefore futile. The model presented here is of heuristic value since it improves our understanding of invasions, and of management value since it defines the data and models needed for predicting invasions.     

Active and resting metabolism in birds: allometry, phylogeny and ecology

Variation in resting metabolic rate is strongly correlated with differences in body weight among birds. The lowest taxonomic level at which most of the variance in resting metabolic rate and body weight is evident for the sample is among families within orders. The allometric exponent across family points is 0.67. This exponent accords with the surface area interpretation of metabolic scaling based on considerations of heat loss. Deviations of family points from this allometric line are used to examine how resting metabolic rates differ among taxa, and whether variation in resting metabolic rate is correlated with broad differences in ecology and behaviour. Despite the strong correlation between resting metabolic rate and body weight, there is evidence for adaptive departures from the allometric line, and possible selective forces are discussed.
The allometric scaling of active metabolic rate is compared with that of resting metabolic rate. The allometric exponents for the two levels of energy expenditure differ, demonstrating that active small-bodied birds require proportionately more energy per unit time above resting levels than do active large-bodied birds. No consistent evidence was found to indicate that the different methods used to estimate active metabolic rate result in systematic bias. Birds require more energy relative to body size when undertaking breeding activities than at other stages of the annual cycle.     

Plant endemism in two forests in southern Bahia, Brazil

An important factor in determining species rarity is the geographic distribution of species. Estimates were made of the level of endemism of the flora of two sites in the southern Bahian wet forest zone. Estimates were made for endemism in the Atlantic forest biome and for the much more restricted area of southern Bahia and northern Espi´rito Santo and are derived from analyses of the distributions of the species known from each area. The species checklist for each area is based on identified specimens resulting from intensive collecting in a forest near Serra Grande (40km north of Ilhe´us) and the Una Biological Reserve (40km south of Ilhe´us). Slightly less than half of the species (45.2% at Una and 47.7% at Serra Grande) have widespread distributions and 7.4% at each site are disjunct between the coastal forests and Amazonia. In the Una Reserve, 44.1% of the species are endemic to the coastal forest and 28.1% endemic to southern Bahia and northern Espi´rito Santo. At Serra Grande, 41.6% of the species are endemic to the coastal forest and 26.5% endemic to southern Bahia and northern Espi´rito Santo.     

Unusual allometry between respiration rate and body size in Chaoborus species

The respiration rates of all four instars of Chaoborus flavicanswere measured with a flow-through respirometer at an experimentaltemperature of 20°C. The respiration rates (µg O₂larva^-1 h^-1) increased parallel to the larval stages accordingto R = 0.027 x W^0.416 (W = µg dry weight), reaching arespiration rate eight times higher for instar IV than for instarI. The slope of the increase with body weight was as low asin two tropical Chaoborus species and was considerably lowerthan usually found for other aquatic animals. Instar IV larvaecollected in the spring showed a significantly higher respirationrate than those collected in the fall. The respiration rateof the fourth instar approximately doubled with a Q₁₀ of 2.1when the experimental temperature was increased from 10 to 20°C.     

Density—body size allometry does not exist in a chironomid community on Myriophyllum

SUMMARY.

• 1 It has been proposed that population density is allometrically related to body size for a wide range of animal species. An interesting question is whether this applies to species within a specific community or trophic guild, thus constituting a ‘pattern’ of community structure.
• 2 Density-body size allometry can be translated into the relationship between population biomass (B) and population density (N). If the regression coefficient b in log B = a + b log N approximates 1, there is no allometric relation between density and body size.
• 3 Data from an epiphytic chironomid community show b～1, thus indicating that no density-body size allometry exists in this community.
• 4 Biomass is less equitably distributed than numbers among species in this and many other communities.
• 5 There is some difficulty in extending the logic of the density-body size allometry to many invertebrate communities, where body size is a strongly time-dependent, variable trait.

     

Fruit fall in tropical and temperate forests: implications for frugivore diversity

There have been few attempts to compare fruit productivity throughout the world, although this is indispensable for understanding the global variations in frugivore diversity. The purposes of this study are (1) to reveal the patterns in fruit fall in tropical and temperate forests, (2) to examine the environmental factors (location, climate, and total litterfall) affecting these patterns, and (3) to assess the effect of fruit fall on frugivore diversity by using bird and primate data. Fruit fall was compared among 53 forests, from around the equator to the cool-temperate zone at 62°N, in Asia, Africa, North and South America, and Australia. Average ± SD of fruit fall (kg/ha/year) was 454 ± 258 in tropical, and 362 ± 352 in temperate forests. Fruit fall was exceptionally high in Australia (812 ± 461). When Australia was excluded, fruit fall significantly decreased with increasing absolute latitude and altitude, and fruit fall in tropical forest was 1.7 times larger than that in temperate forests (265 ± 227). Total litterfall affected fruit fall significantly, explaining 32, 28, and 64% of the variations of fruit fall in the entire data, tropical data, and temperate data, respectively. The fruit fall/litterfall ratio did not differ between temperate and tropical forests but was significantly higher in Australia than in other regions. Among climatic parameters (annual temperature, precipitation, actual evapotranspiration), a positive relationship was found between temperature and fruit fall in the entire dataset and within temperate forests. Fruit fall seemed to explain the temperate/tropical difference in frugivorous primate diversity to some extent, but not for frugivorous bird diversity. This study shows that the difference in fruit fall in tropical and temperate forests is smaller than that in frugivore diversity, and that it could explain at least part of the frugivore diversity.     

Comparative morphology of the prothoracic leg in heliconian butterflies: Tracing size allometry,podite fusions and losses in ontogeny and phylogeny

Prothoracic legs of heliconian butterflies (Nymphalidae, Heliconiinae, Heliconiini) are reduced in size compared to mesothoracic and metathoracic legs. They have no apparent function in males, but are used by females for drumming on host plants, a behavior related to oviposition site selection. Here, taking into account all recognized lineages of heliconian butterflies, we described their tarsi using optical and scanning electron microscopy and searched for podite fusions and losses, and analyzed allometry at the static, ontogenetic and phylogenetic levels. Female tarsi were similar, club-shaped, showing from four to five tarsomeres, each bearing sensilla chaetica and trichodea. Male tarsi were cylindrical, formed from five (early diverging lineages) to one (descendant lineages) either partially or totally fused tarsomeres, all deprived of sensilla. Pretarsi were reduced in both sexes, in some species being either vestigial or absent. Tarsal lengths were smaller for males in almost all species. An abrupt decrease in size was detected for the prothoracic legs during molting to the last larval instar at both histological and morphometric levels. In both sexes, most allometric coefficients found at the population level for the prothoracic legs were negative compared to the mesothoracic leg and also to wings. Prothoracic tarsi decreased proportionally in size over evolutionary time; the largest and smallest values being found for nodes of the oldest and youngest lineages, respectively. Our results demonstrate that evolution of the prothoracic leg in heliconian butterflies has been based on losses and fusions of podites, in association with negative size allometry at static, ontogenetic and phylogenetic levels. These processes have been more pronounced in males. Our study provided further support to the hypothesis that evolution of these leg structures is driven by females, by changing their use from walking to drumming during oviposition site selection. In males the leg would have been selected against due to absence of function and thus progressively reduced in size, in association with podites fusions and lost.     

Effects of allometry,productivity and lifestyle on rates and limits of body size evolution

Body size affects nearly all aspects of organismal biology, so it is important to understand the constraints and dynamics of body size evolution. Despite empirical work on the macroevolution and macroecology of minimum and maximum size, there is little general quantitative theory on rates and limits of body size evolution. We present a general theory that integrates individual productivity, the lifestyle component of the slow–fast life-history continuum, and the allometric scaling of generation time to predict a clade''s evolutionary rate and asymptotic maximum body size, and the shape of macroevolutionary trajectories during diversifying phases of size evolution. We evaluate this theory using data on the evolution of clade maximum body sizes in mammals during the Cenozoic. As predicted, clade evolutionary rates and asymptotic maximum sizes are larger in more productive clades (e.g. baleen whales), which represent the fast end of the slow–fast lifestyle continuum, and smaller in less productive clades (e.g. primates). The allometric scaling exponent for generation time fundamentally alters the shape of evolutionary trajectories, so allometric effects should be accounted for in models of phenotypic evolution and interpretations of macroevolutionary body size patterns. This work highlights the intimate interplay between the macroecological and macroevolutionary dynamics underlying the generation and maintenance of morphological diversity.     

Static allometry of mammalian teeth and the correlation of tooth size and body size in contemporary mammals

Functional least squares regression was used to fit the allometric equation, y = bx^k, to data on head-body lengths and body weights for 123 species of mammals. These measurements were found to be highly correlated and to scale isometrically. The scaling of M ₁ area with head-body length was investigated for 288 species of terrestrial mammals. A method was described for estimating the body size of extinct mammals from M ₁ area and the tooth size-body size relationships discovered among contemporary forms.     

Ambulacral growth allometry in edrioasteroids: functional surface‐volume change in ontogeny and phylogeny

McKinney, M. L. & Sumrall, C. D. 2010: Ambulacral growth allometry in edrioasteroids: functional surface‐volume change in ontogeny and phylogeny. Lethaia, Vol. 44, pp. 102–108. Most organisms do not maintain geometric similarity as they grow, in large part because of surface‐volume interactions. Because respiratory and food‐acquiring organs are dependent on surface area, which increases more slowly than volume, organisms have evolved many strategies to increase the efficiency of, and/or the functional surface areas of these organs. Here, we report some preliminary results comparing area of the feeding apparatus (ambulacra) versus the volume of the theca for a suite of isorophid edrioasteroid species at various ontogenetic sizes. Regression of log (ambulacral area) on log (thecal volume) indicates a strongly constrained allometric pattern whereby the ontogenies of all measured species fall on or near the same line (r² = 0.962, n = 55), with a slope (k) = 0.654 (± 0.018). This slope and associated 0.05 standard error (0.618–0.690) is within the bounds of that expected from increasing surface area to keep pace with the metabolic demands of increasing thecal size. This allometric value is also comparable to the size scaling of metabolism and respiratory and feeding surfaces in many living and a few fossil invertebrates (k ～ 0.5–0.9). The edrioasteroid species analysed show a very wide variety of changes in ambulacral length, width and sinuosity, documenting many different patterns for achieving the same goal of increasing surface area to keep pace with volume increase. There is no evidence of increasing feeding efficiency. □Edrioasteroid, allometry, ambulacrum, surface‐volume, echinoderm.     

Seed size: phylogeny and adaptation in two closely related Proteaceae species-pairs

Summary We studied seed size, seed nutrient status and seedling growth of two closely related fynbos Proteaceae species-pairs growing on juxtaposed soils of different nutrient and moisture status. Seeds had a greater mass and higher phosphorus and nitrogen contents for species occurring on limestone (higher nutrient and moisture contents) than those on the colluvial sands (lower nutreints and moisture). This trend was found within, but not across genera, stressing the importance of phylogeny in interpreting adaptations. It would be difficult to test for the effects of either nutrients or moisture separately, since the same advantage of enhanced seedling size, and hence survival in a stressed environment, applies to both factors. The increased root: shoot ratios (using lengths) of the Leucadendron species relative to the Protea species are interpreted as an attempt to overcome a phylogenetic constraint that results in smaller seed size in the former genus.     

Reproductive constraints,not environmental conditions,shape the ontogeny of sex‐specific mass–size allometry in roe deer

In polygynous mammals, sex‐specific patterns of body growth are linked to divergent selection pressures on male and female body size, resulting in sexual dimorphism (SD). For males, reproductive success is generally linked to body size, hence, males should prioritise early growth. For females, reproductive success is linked to resource availability, so they may adopt a more conservative growth tactic. Using longitudinal monitoring of known‐age animals in two contrasting populations and an allometric approach to disentangle the relative contribution of structural size and physiological condition to SD, we addressed these issues in the weakly polygynous roe deer. Despite very different environmental conditions, we found remarkably similar patterns in the two populations in the mass–size allometric relationship at each life history stage, suggesting that relative allocation to structural size and physiological condition is highly constrained. SD in structural size (indexed by hind foot length) involved sex‐specific growth trajectories governed by a single mass–size allometric relationship during the juvenile stage, such that males were both bigger and heavier than females. In contrast, SD in physiological condition (indexed by the allometric relationship between body mass and hind foot length, expressed as body mass for a given body size) developed markedly during the sub‐adult stage in relation to sex differences in the timing of first reproduction. Among adults, males were heavier for a given size than females, suggesting that, relative to females, males express a capital breeder tactic, accumulating fat reserves to offset reproductive costs. By the senescent stage, SD in physiological condition had disappeared, with both sexes governed by a single allometric relationship, suggesting more rapid senescence in males than females. Individuals born into poor cohorts were generally lighter for a given size, indicating growth priority for skeletal size over physiological condition in both sexes. However, sex differences in cohort effects among sub‐adults resulted in lower size‐specific SD in poor cohorts, indicating that body condition of sub‐adult females is buffered against environmental harshness. We conclude that sex‐differences in reproductive tactics impose constraints on the ontogeny of SD in roe deer, leading to sex‐specific trajectories in structural size and physiological condition.     

Element interactions in forest ecosystems: succession,allometry and input-output budgets

Element interactions within forests differ from those in other major ecosystems for three major reasons: — a greater allocation of carbon to structural material; — a greater element storage within biomass; and — the diversity of carbon- and nutrient-containing metabolites produced. The most important of these differences is structural material, which can lead to C: element ratios in biomass (as a whole) 100 × greater than those in unicellular organisms. Stand allometry causes the amount of carbon stored and C:element ratios in biomass to change in predictable ways in the course of secondary succession. Such changes affect microbial dynamics and C: element interactions within soils. Bicarbonate, organic acids, nitrate, phosphate, and sulfate are major anions within forest soils: they control leaching of both anions and cations. Biotic interactions of C, N, P, and S during both uptake and mineralization control the potential for production of these anions within forests, and geochemical interactions regulate their mobility and loss.     

Functional diversity in fruit‐frugivore interactions: a field experiment with Mediterranean mammals

Using field seed sowings, we assessed how four mammal species (Meles meles, Vulpes vulpes, Sus scrofa, and Oryctolagus cuniculus) influenced seed germination in three fleshy‐fruited Mediterranean shrubs (Corema album, Pyrus bourgaeana, and Rubus ulmifolius). We predicted that gut passage and removal away from mother plants would enhance the quantity, speed, and asynchrony of seed germination. Results showed that percent germination was altered by gut passage, but that the magnitude and even the direction of such effects varied according to plant and disperser species. Likewise, dispersal away from mother plants affected the percentage and germination speed in some species but not others. Gut passage increased asynchrony of germination in Rubus and Pyrus, and removal from the mother plant increased asynchrony in Rubus, which likely enhances plant fitness in unpredictable environments. Gut passage generally had a stronger effect on germination than removal away from mother plants, but for some species both factors were similarly influential. Therefore, the combined effects of both seed dispersal services varied individually among fruit and frugivore species, leading to unusually high functional diversity in this seed dispersal mutualism.     

The roles of body size and phylogeny in fast and slow life histories

Species’ life histories are often classified on a continuum from “fast” to “slow”, yet there is no consistently used definition of this continuum. For example, some researchers include body mass as one of the traits defining the continuum, others factor it out by analysing body-mass residuals, a third group performs both of these analyses and uses the terms “fast” and “slow” in both ways, while still others do not mention body mass at all. Our analysis of European and North American freshwater fish, mammals, and birds (N = 2,288 species) shows the fundamental differences between life-history patterns of raw data and of body-mass residuals. Specifically, in fish and mammals, the number of traits defining the continuum decreases if body-mass residuals are analysed. In birds, the continuum is defined by a different set of traits if body mass is factored out. Our study also exposes important dissimilarities among the three taxonomic groups analysed. For example, while mammals and birds with a “slow” life history have a low fecundity, the opposite is true for fish. We conclude that our understanding of life histories will improve if differences between patterns of raw data and of body-mass residuals are acknowledged, as well as differences among taxonomic groups, instead of using the “fast–slow continuum” too indiscriminately for any covarying traits that appear to suit the idea.     

Fungal endophyte communities in two tropical forests of southern India: diversity and host affiliation

Fifteen tree species from a tropical dry thorn forest and fifteen tree species from a tropical dry deciduous forest in the Mudumalai Wildlife Sanctuary, Nilgiri Biosphere Reserve, southern India, were surveyed for their foliar endophyte communities during the dry and wet seasons. Surface sterilized leaf segments of uniform dimension were plated on nutrient agar and culturable endophytes growing from the segments were identified. Endophyte diversity was greater in the dry thorn forest than in the dry deciduous forest in the dry season. Although the isolation frequency of culturable endophytes increased for both forests during the wet season, the assemblages were represented not by any unique fungal species but by the commonly occurring ones. Furthermore, although individual leaves were densely colonized by endophytes, only a few species of endophytes colonized the whole leaves; and, only a few fungal species dominated the foliar endophytic communities and were common for both forests during both dry and wet seasons. Thus, even under wet conditions that favour dispersal and infection by fungi, the endophyte diversity increased only marginally, an indication that certain tropical forests are not hyperdiverse with reference to fungal endophytes. This should be considered when using culturable endophyte diversity as a surrogate for estimating global fungal diversity.