Life History Categories Research Articles

Environmental DNA Characterization of the Fish Species Composition in the Mukawa River and Adjacent Habitats

The diverse freshwater fish fauna of the Japanese archipelago is distributed among four main island landmasses, which include Hokkaido in the north, with many diadromous species. One relatively well-preserved river drainage along the southern coast of Central Hokkaido is the Mukawa River. Fish fauna surveys in the Mukawa River were mostly in downstream areas and the fish diversity is not well-documented among the upper, lower river, and coastal environments. Fish communities in the river, estuary, and sea were sampled using eDNA analysis to evaluate upstream and downstream species detections, and tidal and spatial detection variation near the river mouth. The number of species was higher at the river mouth and nearshore sites compared to the river and offshore. Fish detections reflected life history categories (freshwater resident, diadromous, brackish, or marine) and the environments. Similarity analysis showed that fish species compositions were divided into (1) upstream and midstream, (2) downstream and river mouth, (3) adjacent shore, and (4) offshore. Salmonid, cyprinid, loach, and sculpin species were detected in the river, compared to a mixture of species downstream and along the coast. This rapid assessment type study demonstrated that eDNA survey methodology would be effective for multiple river comparative surveys, seasonality studies, or evaluating possible effects of cross-river weirs or dams.

Cetaceans Humerus Radiodensity by CT: A Useful Technique Differentiating between Species, Ecophysiology, and Age.

Simple SummaryCetaceans are marine mammals whose tissues have undergone an evolutionary process to adapt to life in the aquatic medium. In addition, depending on the species, the adaptations will have developed differently. However, some features of the bones of these animals are still poorly studied, and a good technique for analysing this tissue is computed tomography. With this, it is possible to measure bone density, compare bone density between distinct species, and then relate it with the ecophysiological aspects of the animal. For this reason, this study aimed to create a protocol to measure the bone radiodensity of the humerus of cetaceans through computer tomography. The purpose was to be able to make comparisons between different species to advance the understanding of this cetacean tissue. This project considered two species with different characteristics and behaviours: the Atlantic spotted dolphin (Stenella frontalis) and the pygmy sperm whale (Kogia breviceps). The main results observed were significant differences in bone density between different types of bone (trabecular and cortical bone) and various portions of the humerus within a given species. Such differences were also observed between species with varying habits of diving (shallow divers and deep divers) and distinct swimming habits (swimming style with low-medium energy expenditure and swimming style that requires medium-high energy consumption rates). These results allow us to consider the unique adaptations of this tissue to adapt to varying lifestyles of these animals in the aquatic ecosystem. Therefore, this technique will allow for comparisons to distinguish different characteristics related to species, age, diving behaviour, and swimming style.Cetaceans are mammals that underwent a series of evolutionary adaptations to live in the aquatic environment, including morphological modifications of various anatomical structures of the skeleton and their bone mineral density (BMD); there are few studies on the latter. BMD is related to the radiodensity measured through computed tomography (CT) in Hounsfield units (HU). This work aimed to test and validate the usefulness of studying humeral bone radiodensity by CT of two cetacean species (the Atlantic spotted dolphin and the pygmy sperm whale) with different swimming and diving habits. The radiodensity was analysed at certain levels following a new protocol based on a review of previous studies. Humeral radiodensity values were related to four aspects: species, diving behaviour, swimming activity level, and age. We observed that the consistent differences in the radiodensity of the cortical bone of the distal epiphysis between animals of different life-history categories suggest that this bone portion could be particularly useful for future ontogenetic studies. Hence, this technique may be helpful in studying and comparing species with different ecophysiologies, particularly distinguishing between swimming and diving habits.

Modeling effects of disturbance across life history strategies of stream fishes.

A central goal of population ecology is to establish linkages between life history strategy, disturbance, and population dynamics. Globally, disturbance events such as drought and invasive species have dramatically impacted stream fish populations and contributed to sharp declines in freshwater biodiversity. Here, we used RAMAS Metapop to construct stage-based demographic metapopulation models for stream fishes with periodic, opportunistic, and equilibrium life history strategies and assessed their responses to the effects of invasion (reduced carrying capacity), extended drought (reduced survival and fecundity), and the combined effects of both disturbances. Our models indicated that populations respond differentially to disturbance based on life history strategy. Equilibrium strategists were best able to deal with simulated invasion. Periodic strategists did well under lower levels of drought, whereas opportunistic strategists outperformed other life histories under extreme seasonal drought. When we modeled additive effects scenarios, these disturbances interacted synergistically, dramatically increasing terminal extinction risk for all three life history strategies. Modeling exercises that examine broad life history categories can help to answer fundamental ecological questions about the relationship between disturbance resilience and life history, as well as help managers to develop generalized conservation strategies when species-specific data are lacking. Our results indicate that life history strategy is a fundamental determinant of population trajectories, and that disturbances can interact synergistically to dramatically impact extinction outcomes.

Physiological consequences of biologic state and habitat dynamics on the critically endangered Yangtze finless porpoises (Neophocaena asiaeorientalis ssp. asiaeorientalis) dwelling in the wild and semi-natural environment.

The objectives of this study were to investigate the effects of habitat and biological state on the physiology of critically endangered wild and semi-natural Yangtze Finless Porpoises (YFPs; Neophocaena asiaeorientalis ssp. asiaeorientalis) by measuring and comparing serum biochemical parameters. A total of 168 YFPs were sampled, 68 living in the semi-natural (Tian-E-Zhou Oxbow) and 98 living in the wild (Poyang Lake, PL) environment. The YFPs in the Tian-E-Zhou Oxbow were sampled from 2002 to 2015 and in the PL from 2009 to 2017. Each population was divided into Juvenile Male, Juvenile Female, Adult Male, Pregnant and Lactating Female life history categories. Overall, with location, 19/33 of the analytes and with season 18/33 of the analytes were significantly different. Similarly, within each location, 15/33 of the analytes changed with time in PL while only 8/33 changed with time in Tian-E-Zhou Oxbow, respectively. Finally, 15/33 of the analytes demonstrated significant differences between the different age and sex groups of animals. In our study, a significant variation, as well as an increasing and decreasing pattern of several parameters in both populations, suggest a worsening ecological environment of both habitats. This study will help in health assessment, improving conservation and management practices, a crucial requisite for biodiversity conservation.

Hematologic and biochemical differences between two free ranging Yangtze finless porpoise populations: The implications of habitat.

The goals of this study were to compare the serum chemistry and hematology values of wild and semi-natural free-ranging Yangtze Finless Porpoises (Neophocaena asiaeorientalis ssp. asiaeorientalis) populations and to ascertain how these values change with the different environmental condition. For this study, samples were collected from 81 YFPs, 35 living in the wild and 46 living in a semi-natural reserve. Each population was divided into 8 life history categories; Male Calf, Female Calf, Juvenile Male, Juvenile Female, Adult Male, Pregnant, Lactating and Pregnant plus Lactating. Statistically significant differences in the various parameters were observed in the same life history categories for both populations. Generally, Lipid Profile, Hepatic Enzymes, Creatine Kinase, Red Blood Cells, Hemoglobin, Hematocrit and Neutrophils were significantly higher in the Tian-E-Zhou Oxbow population while, Creatinine, Phosphate, Lactate Dehydrogenase, Bilirubin and Lymphocytes were significantly higher in the Poyang Lake YFPs. Across the groups in the Tian-E-Zhou Oxbow population, a significant decrease in serum Albumin, Alkaline Phosphatase and Calcium, while a significant increase in the Neutrophils and Platelets was observed. Similarly, in the Poyang Lake, Alkaline Phosphatase levels in the Female Calves group, High Density Lipoprotein Cholesterol in Lactating group, basophil counts in Pregnant plus Lactating group, lymphocytes counts in Juvenile Females group and Globulin and Total Protein levels in Pregnant group were significantly higher. This study in health assessments can help us to understand the effect of sex, age, reproductive status and environmental conditions on the well-being of Yangtze Finless Porpoises.

Life History Diversity in Klamath River Steelhead

AbstractOncorhynchus mykiss exhibits a vast array of life histories, which increases its likelihood of persistence by spreading risk of extirpation among different pathways. The Klamath River basin (California–Oregon) provides a particularly interesting backdrop for the study of life history diversity in O. mykiss, in part because the river is slated for a historic and potentially influential dam removal and habitat recolonization project. We used scale and otolith strontium isotope (87Sr/86Sr) analyses to characterize life history diversity in wild O. mykiss from the lower Klamath River basin. We also determined maternal origin (anadromous or nonanadromous) and migratory history (anadromous or nonanadromous) of O. mykiss and compared length and fecundity at age between anadromous (steelhead) and nonanadromous (Rainbow Trout) phenotypes of O. mykiss. We identified a total of 38 life history categories at maturity, which differed in duration of freshwater and ocean rearing, age at maturation, and incidence of repeat spawning. Approximately 10% of adult fish sampled were nonanadromous. Rainbow Trout generally grew faster in freshwater than juvenile steelhead; however, ocean growth afforded adult steelhead greater length and fecundity than adult Rainbow Trout. Although 75% of individuals followed the migratory path of their mother, steelhead produced nonanadromous progeny and Rainbow Trout produced anadromous progeny. Overall, we observed a highly diverse array of life histories among Klamath River O. mykiss. While this diversity should increase population resilience, recent declines in the abundance of Klamath River steelhead suggest that life history diversity alone is not sufficient to stabilize a population. Our finding that steelhead and Rainbow Trout give rise to progeny of the alternate form (1) suggests that dam removal might lead to a facultatively anadromous O. mykiss population in the upper basin and (2) raises the question of whether both forms of O. mykiss in the Klamath River should be managed under the same strategy.Received June 20, 2015; accepted October 16, 2015

Prevalence and anatomic site of Crassicauda sp. infection, and its use in species identification, in kogiid whales from the mid‐Atlantic United States

AbstractThe parasitic nematode Crassicauda sp. was initially described in kogiid whales from specimens collected within cervical tissues, uncommon sites of infection for this parasite. Crassicauda sp. has only been reported in Kogia breviceps to date, but no study has yet investigated a large sample of both kogiid species. A 15 yr record of 104 kogiid strandings (K. sima, n = 40; K. breviceps, n = 64) in North Carolina and Virginia, U.S.A. was used to determine the prevalence of Crassicauda sp. across species, within species across sex, and within sex across length and life history categories. Crassicauda sp. was confirmed to be a species‐specific parasite among kogiids infecting only K. breviceps (prevalence = 45%). Within K. breviceps, prevalence was similar (45%) in both immature and mature males, but increased from 10% in immature to 76% in mature females. This study confirmed the cervico‐thoracic distribution of the parasite, and identified a novel site of infection in a previously undescribed exocrine gland associated with the pigmented “false gill slit.” The species‐specific nature of Crassicauda sp. infection, the exocrine gland, and the distinct features of the false gill slit pigmentation associated with the gland, are all useful characters to identify kogiid species in the field.

Dispersal, dormancy and life-history tradeoffs at the individual, population and species levels in southern African Asteraceae.

Dispersal and dormancy are important risk-reducing strategies in unpredictable environments. Negative covariation between these strategies is theoretically expected, but empirical evidence is limited and inconsistent. Moreover, covariation may be affected by other life-history traits and may vary across levels of biological organization. We assessed dispersal (vertical fall time of fruits, a proxy for wind dispersal ability) and dormancy (germination fractions measured during germination trials) in populations of 15 annual and 12 perennial wind-dispersed species in six Asteraceae genera from South Africa. Dormancy was higher in annuals than in perennials, whereas fall time was largely determined by evolutionary history. Controlling for phylogeny, dispersal and dormancy was negatively associated across species and life-history categories. Negative covariation between dispersal and dormancy was not evident at either the individual level (except for seed heteromorphic species) or the population level. Our study provides rare empirical support for the theoretical expectation of tradeoffs between dormancy and the alternative risk-reducing strategies, perenniality and dispersal, but refutes the expectation of increased dispersability in perennials. Although negative covariation between dispersal and dormancy at the species level appears not to be a simple consequence of upscaling individual-level mechanistic tradeoffs, our findings suggest that selection for one strategy may constrain evolution of the other.

Ontogenetic allometry and body composition of the common bottlenose dolphin (Tursiops truncatus) from the U.S. mid‐Atlantic

AbstractGrowth in common bottlenose dolphins (Tursiops truncatus) was investigated through examination of sex‐specific, ontogenetic changes in the mass of 38 discrete body compartments, utilizing stranded dolphins in good body condition (n = 145). Ontogenetic allometry and the body composition technique were used to quantitatively describe growth patterns. Although adult males were significantly larger than adult females in total body mass (TBM) and total length, overall patterns of growth were remarkably similar between sexes. The integument, locomotor muscle, and vertebral column together represented 50%–58% of TBM across all life history categories, although their relative contributions varied ontogenetically. Young dolphins invested the greatest percentage of TBM in integument, while locomotor muscle was the single largest body component in adults. In both sexes (1) most muscle groups displayed positive allometry, (2) most skeletal elements displayed negative allometric or isometric growth, (3) most abdominal viscera associated with digestion displayed positive allometry, and (4) the brain displayed negative allometric growth. Reproductive tissues exhibited the highest rates of growth in both sexes, and increased as a percentage of TBM with maturity. This study provides an integrated view of bottlenose dolphin growth and a quantitative baseline of body composition for future monitoring of this sentinel species of ecosystem health.

Thermoregulatory Scope Associated with Underwater Exercise in a Polar Seal

A weakness in predicting habitat change impacts in polar regions is that little is known about thermoregulatory energetics in high‐latitude seals. To better understand thermoregulatory range associated with the partitioned air‐water habitat of ice seals, we collected skin surface heat flux data from 42 free‐ranging Weddell seals over 1‐13 day deployments. We modeled total body heat dissipation from heat flux data to address the thresholds of basal versus activity‐derived heat loss over a range of swim speeds. As body size/condition affect heat loss and may manifest as altered thresholds for thermal homeostasis, we compared 4 life history categories—pups, juveniles, non‐reproductive adult females and post‐weaning females. Preliminary evidence indicates obligate heat dissipation, reflecting thermoregulatory costs, is elevated in water versus air, and locomotory heat generation offsets these costs. Dive activity‐heat loss relationships were compared among the 4 life history stages to detect differences in baseline obligate heat loss and threshold swim speeds for thermal substitution. Group differences were apparent under non‐steady state conditions such as transition from haul‐out to water, where post‐weaning females lost more heat than good condition skip breeder females (+40% W/m2 heat loss). Juveniles, with limited blubber insulation, also lost more heat than pups on initial water entry. Continued efforts to quantify and model thermoregulatory thresholds will provide important insights into the ability of polar pinnipeds to respond to changing ice conditions.

Topographical distribution of blubber in finless porpoises (Neophocaena asiaeorientalis sunameri): a result from adapting to living in coastal waters.

Blubber has many functions, among which energy storage, thermoregulation, buoyancy, and hydrodynamic streamlining are the most frequently cited. Within and between taxa, variations in its structure and distribution likely reflect different adaptations of a species to its life history requirements, environment, health, and function. Here, we use ultrasound to describe the distribution of blubber in the finless porpoise (Neophocaena asiaeorientalis sunameri) based on examinations of 34 fresh cadavers recovered as accidental fisheries bycatch. Measurements of blubber depth determined by ultrasound positively correlated with conventional measurements using a scalpel and calipers. Whereas conventional surgical incision and visual examination revealed two layers of blubber, ultrasound revealed up to three layers; thus, ultrasound reveals additional structural detail in blubber while crude necropsy techniques do not. Across life history categories, ultrasound revealed the distribution of inner blubber to be topographically consistent with that of full-depth blubber. Blubber in the dorsal region was stratified into three layers and was significantly thicker than that in the lateral and ventral regions, in which a middle layer was normally absent. Ultrasoundprovides a fast, effective, and accurate means to determine blubber thickness and structure, and thus, assessment of the health of fresh finless porpoise carcasses. Blubber depth is determined largely by the thickness of the inner and middle layers, wherein lipids are concentrated. The thickening of blubber in the dorsal thoracic-abdominal region suggests multiple roles of thermal insulation, lipid storage, and, we speculate, to facilitate vertical stability in the complex shallow and estuarine waters in which this animal absent of a dorsal fin occurs.

Profiling heat loss in an extreme polar mammal, the Weddell seal

A major weakness in predicting habitat change impacts in polar regions is that little is actually known about energetic costs of basic thermoregulation in high‐latitude seals and other apex predators. Characteristics of body size and condition (surface area: volume ratios, insulation) are likely to affect heat loss and manifest as altered thresholds for thermal homeostasis. We monitored the thermal interface between animal‐environment directly via skin surface heat flux sensors (HFS) and indirectly with infrared thermography (IRT) in Weddell seals (n=42) over 2–7d. Utilizing 4 life history categories—pups, juveniles, non‐reproductive adult females (skip breeders) and post‐weaning females—we tested for effect of body size and known insulation patterns (blubber depth via imaging ultrasound). IRT surface temperature maxima and range suggested 4 sites of interest for HFS placement and continued monitoring: axilla (variable hot), head (hot), flank (variable cold) and neck (cold). IRT‐generated surface temperature distribution histograms further permitted the partitioning of body surface area such that an integrated thermal profile could be modeled from HFS data collected at these 4 sites. With this tool we can for the first time examine thermal homeostasis in free‐ranging seals over a range of potentially changing environments. Funded by NSF Polar Programs.

Reproductive Decisions among People Living with Human T-cell Lymphotropic Virus Type 1 (HTLV-1)

Background: Human T-cell Lymphotropic Virus type 1 (HTLV-1) infection is a neglected public health problem. The majority of carriers is asymptomatic and may have a low risk of developing related diseases. The aims of this study were to discuss reproductive decisions of women and men living with HTLV-1 infection to assess their perception of infection and associated diseases, expectations regarding Mother-to-Child Transmission (MTCT), and whether health care conditions may affect their reproductive decisions. Methods: A qualitative study with 13 adult HTLV-1-seropositive subjects without co-infections. For data analysis, life history trajectories and categories of discourse were constructed for each respondent. Results: Reproductive decisions required the reassessment of life projects in the new context of HTLV-1 infection. Thus, a child remains representative of a “new meaning to life”. There is a need for accurate information regarding the risk of MTCT and the transmission risk to a serodiscordant partner while trying to conceive. It was also observed that a couple’s relationship and emotional dynamics were crucial in the process of making reproductive decisions. It was emphasized that the inhibition of breastfeeding was seen as a reliable method in preventing transmission, favouring the decision to have a child. Conclusions: Reproductive decisions were influenced by information transmitted by healthcare providers that only rarely does a person with HTLV-1 become sick due to the infection. Because this infection is incurable, reproductive decisions are crucial. The importance of reproductive decisions highlight the need for accurate information dissemination and infection prevention, perhaps only made possible through effective interdisciplinary means.

Community Assembly in the Salamander Genus Desmognathus

In this paper, I present a model of community assembly in the salamander genus Desmognathus based on a survey of assemblage composition throughout the range of the genus. The 21 species of Desmognathus can be sorted into three life-history categories, namely, stream, streamside, and forest, based on duration of the larval phase and a suite of other life-history and morphological traits that are correlated with habitat use of the several life-history stages. In most assemblages having all three life-history categories, stream species are larger than streamside species, and the latter species are larger than forest species. An evaluation of the literature on interspecific competition and predation (i.e., intraguild predation) in Desmognathus indicates that these processes are important in structuring assemblages of these salamanders. Thus, niche assembly, as opposed to dispersal assembly (i.e., neutral model), seems to be a valid model of community assembly in Desmognathus. Only streamside species occur throughout the range of the genus, and these forms alone are found around the periphery of the range. One to three streamside species form the base of extant assemblages of Desmognathus, with stream and forest species contributing to the more diverse assemblages of the southern Appalachian region. The maximum numbers are two or three streamside species, two or three stream species, and two forest species, although assemblages of more than six species are undocumented. I suggest that the rapid evolutionary diversification in body size and life history in Desmognathus that has generated the complex assemblages of this genus in the Appalachians has been facilitated by a high level of life-history symmetry in these salamanders.

What are the key drivers of spread in invasive plants: dispersal, demography or landscape: and how can we use this knowledge to aid management?

Invasive plants disrupt ecosystems from local to landscape scales. Reduction or reversal of spread is an important goal of many invasive plant management strategies, but few general guidelines exist on how to achieve this aim. We identified the main drivers of spread, and thus potential targets for management, using a spatially explicit simulation model tested on different life history categories in different spread and landscape scenarios. We used boosted regression trees to determine the parameters that most affected spread. Additionally, we analysed how spread reacted to changes in those parameters over a broad realistic range. From our results we deduce four simple management guidelines: (1) Manage dispersal if possible, as mean dispersal distance was an important driver of spread for all life history categories; (2) short bursts of rapid spread or more usual year on year spread can have different drivers, therefore managers need to decide what type of spread they want to slow; (3) efforts to manage spread will have variable outcomes due to interactions between, and non-linear responses to, key drivers of spread; and (4) the most useful demographic rates to target depend on dispersal ability, life history and how spread is measured. Fecundity was found to be important for driving spread only when reduced to low levels and particularly when the species was short lived. For longer lived species management should target survival, or age of maturity, especially when dispersal ability is limited.

The buoyancy of the integument of Atlantic bottlenose dolphins (Tursiops truncatus): Effects of growth, reproduction, and nutritional state

In Atlantic bottlenose dolphins (Tursiops truncatus) the thickness and lipid content of blubber (the integument's specialized hypodermis) varies across ontogeny and with reproductive and nutritional state. Because the integument comprises up to 25% of total body mass in this species, ontogenetic changes in its lipid content may influence whole body buoyancy. The density and volume of the integument were measured and its buoyancy calculated across an ontogenetic series of dolphins and in pregnant and emaciated adults (total n= 45). Regional differences between the metabolically labile trunk integument and the structural tailstock integument were also investigated. Mean densities of both trunk and tailstock integument were similar across life history categories (trunk = 1,040.7 ± 14.1 kg/m3; tailstock = 1,077.1 ± 21.2 kg/m3) and were statistically similar to the density of seawater (1,026 kg/m3). The mean buoyant force of integument from the trunk (−1.01 ± 1.74 N) and tailstock (−0.30 ± 0.21 N) did not vary significantly across ontogeny. In contrast, pregnancy and emaciation did influence the integument's buoyancy, which ranged between 9 N and −45 N in these categories. Although neutral during growth, the integument's contribution to whole body buoyancy can be influenced by an individual's reproductive and nutritional status.

Sex and age influence responses to changes in the cost of cooperative care in a social carnivore

In cooperative breeders, variation in contributions to offspring care will often be determined by variation in the cost of care. Because the cost of investment is determined by its effect on residual reproductive value, a unit of care should impose different fitness costs on different life-history categories of helper. This means that a change in current condition should have category-specific effects on contributions to care. I test this in the cooperatively breeding banded mongoose (Mungos mungo), experimentally increasing the cost of care by subjecting helpers to temporary deprivation. I observed category-specific effects on pup provisioning: For a given percentage weight loss, female helpers reduce their provisioning by a greater extent than male helpers. This is likely to be because variation in condition has a stronger effect on female reproductive success, so females should be under stronger selection to limit the cost of offspring care. I also observed an unexpected effect of age, with older helpers reducing their provisioning by more than younger helpers. This is probably because older helpers are more likely to breed themselves, so changes in condition may have a more immediate effect on direct fitness. In general, category-specific responses to changes in state should occur wherever there are existing category-specific differences in contributions to care, in both cooperative breeders and biparental species. Copyright 2010, Oxford University Press.

Blue fan palm distribution and seed removal patterns in three desert oases of northern Baja California, Mexico

Information on the current processes controlling the distribution patterns of relict palm populations at the limit of their northwestern distribution in America are poorly known. We explored the importance of post-dispersal seed removal by vertebrates, recruitment, and distribution patterns of the blue fan palm, Brahea armata, in the Northern Baja California peninsula, by evaluating (i) the levels of blue fan palm seed removal by vertebrates at two spatial scales and the initial fate of dispersed seeds, (ii) the spatial distribution and association of seedlings and adults at two spatial scales, (iii) seed removal levels and seedling densities based on density and distance to adult palm trees, and (iv) the population age structure. Overall, seed removal levels were low at all sites, varied at regional but not at local scales, with small rodents apparently being responsible of most removals. Adult density and distribution differed among oases, but seedling densities did differ locally. Whereas seed removal did not vary with distance from seed sources or parent trees, a weak positive association between seedlings and adults at the whole patch level indicated that establishment tended to occur in or near those grid cells where adults had established successfully. However, the analysis showed a negative association between seedling and adult densities within the patches, indicating that within the grid cells where growth was most successful, seedlings established preferentially in relatively open spaces. All life-history categories were adequately represented within each site and populations seemed to be in a fairly good conservation state. We did not find evidence to establish that post-dispersal seed removal by rodents is a main factor defining the recruitment patterns in these oases. In contrast, the effect of flood pulses seems to be significant and may have strong and conclusive effects on palm seedling distributions. We suggest that local biotic (nurse plants) and/or abiotic (canyon physiography, nurse objects) factors at each particular canyon have the potential to affect post-dispersal seed removal activity patterns by rodents, as well as to provide vital protection for palm seedling establishment from the extreme floods. This baseline information will help in further investigations on the possible mechanisms that sustain palm populations at their distribution limits and in stressful environments.

Intraguild Interactions and Population Regulation in Plethodontid Salamanders

In this paper I review the contributions of analytic and experimental research on intraguild predation and interspecific competition to our understanding of population regulation in plethodontid salamanders. Henry Wilbur's model of population regulation in amphibians serves as a framework for the arguments. Much of the discussion is based on studies of eastern North American plethodontids that have been the focus of most of the research. Ensembles of plethodontids in this region include species with complex life cycles (i.e., larval development) and simple life cycles (i.e., direct development). Interactions between members of these two life-history categories appear to be weaker than those within categories. Whereas there is no definitive evidence of factors that regulate populations of plethodontid salamanders, interspecific competition and intraguild predation do appear to contribute in some ensembles. Food and space have been identified as limiting resources in interspecific competition. Although predation of larger on smaller salamanders may be relatively rare in nature, the threat of predation appears to promote behavioral responses in members of the smaller species that reduce risks but may lower fitness through other effects. The role of extralimital predators and competitors in regulation of these salamanders is largely untested. Ideally, future research should involve manipulative experiments on unenclosed field plots that examine effects of resources, intraguild competitors and predators, and extralimital predators on populations of key species of plethodontids.

A survey of nuclear ribosomal internal transcribed spacer substitution rates across angiosperms: an approximate molecular clock with life history effects

BackgroundA full understanding of the patterns and processes of biological diversification requires the dating of evolutionary events, yet the fossil record is inadequate for most lineages under study. Alternatively, a molecular clock approach, in which DNA or amino acid substitution rates are calibrated with fossils or geological/climatic events, can provide indirect estimates of clade ages and diversification rates. The utility of this approach depends on the rate constancy of molecular evolution at a genetic locus across time and across lineages. Although the nuclear ribosomal internal transcribed spacer region (nrITS) is increasingly being used to infer clade ages in plants, little is known about the sources or magnitude of variation in its substitution rate. Here, we systematically review the literature to assess substitution rate variation in nrITS among angiosperms, and we evaluate possible correlates of the variation.ResultsWe summarize 28 independently calibrated nrITS substitution rates ranging from 0.38 × 10-9 to 8.34 × 10-9 substitutions/site/yr. We find that herbaceous lineages have substitution rates almost twice as high as woody plants, on average. We do not find any among-lineage phylogenetic constraint to the rates, or any effect of the type of calibration used. Within life history categories, both the magnitude of the rates and the variance among rates tend to decrease with calibration age.ConclusionAngiosperm nrITS substitution rates vary by approximately an order of magnitude, and some of this variation can be attributed to life history categories. We make cautious recommendations for the use of nrITS as an approximate plant molecular clock, including an outline of more appropriate phylogenetic methodology and caveats against over interpretation of results. We also suggest that for lineages with independent calibrations, much of the variation in nrITS substitution rates may come from uncertainty in calibration date estimates, highlighting the importance of accurate and/or multiple calibration dates.