bluuebunny/crossref_metadata_2025 huggingface dataset:
Invulnerable Prey and the Paradox of Enrichment
Authors: Abrams Peter A. , Walters Carl J.
Published: May 2006

In many predator—prey systems, prey individuals make transitions between vulnerable and invulnerable states or locations. The invulnerable (or less vulnerable) class can be individuals occupying a spatial refuge or those engaged in activities that greatly reduce the risk of predation. Simple models are used to show that transitions between such classes have the following consequences: (1) equilibrium prey density increases as the conditions of prey growth are improved and (2) enrichment often cannot destabilize systems with stable equilibrium densities and many stabilize systems that are undergoing limit cycle oscillations. Transitions to and from invulnerable states therefore represent a possible explanation for the lack of examples of destabilization via fertilization (the paradox of enrichment) in nature. Other theoretical reasons for the apparent absence of the paradox or enrichment are reviewed, and methods of distinguishing the different mechanism are discussed.
Covariation of Thermal Biology and Foraging Mode in Two Mediterranean Lacertid Lizards
Authors: Belliure Josabel , Carrascal Luis M. , Diaz Jose A.
Published: May 2006

Body temperatures, heat exchange rates, behavioral thermoregulation, and movement behavior (as an index of foraging mode) were studied in two widely distributed medium—sized lacertid lizards (Acanthodasctylus erythrurus and Psammodromus algirus). P. algirus mainly inhabits broad—leaved forests, whereas A. erythrurus prefers open, sandy areas with sparsely distributed vegetation. These habitat preferences parallel differences between the areas in which both genera presumably originated: Eurosaharian xeric steppes with high operative temperatures (Te) for Acanthodacylus, and Mediterranean open Forest with lower Te for Psammodromus. Field observations showed that percentage of time spent basking and basking rate (number of basks per minute) were negatively related to Te, although average bask duration was not. Percentage of time spent moving, moving rate (number of moves per minute), and the average duration of individual moves were inversely related to Te and were higher in P. algirus. The percentage of total locomotion time that was spent moving in the shade was also higher in P. algirus. Behavioral thermoregulation strategies differed in laboratory thermogradient, where P. algirus basked more often and for shorter periods and selected warmer patches than did A. erythrurus. Selected body temperatures (Tb) in a laboratory thermogradient were significantly higher in A. erythrurus than in P. algirus. Shade Seeking Tb was higher in A. erythrurus, but Resume Basking Tb did not differ significantly between the two species. Heating and cooling rates also differed in the two species: A. erythrurus warmed more slowly and cooled faster than did P. algirus. Our data support the existence of a complex syndrome that combines aspects of the behavior, physiology, and ecology of both species. The thermal consequences of inhabiting a certain type of habitat can be counterbalanced by behavioral and physiological means that, in turn, affect movement and, hence, foraigng behavior. Thus, the more active species (P. algirus) heated faster, cooled more slowly, and basked more often but for shorter periods and at warmer patches than thee less active species (A. Erythrurus).
Winter Habitat Quality, Population Limitation, and Conservation of Neotropical‐Nearctic Migrant Birds
Authors: Sherry Thomas W. , Holmes Richard T.
Published: May 2006

Recent declines in Neotropical—Nearctic migrant songbird populations are often attributed to events during the nonbreeding season, such as tropical habitat conversion and drought. Support for this hypothesis in most species, however, is largely anecdotal or conjectural. There is a dearth of demographic information about migrants on their Neotropical winter grounds. Such data are needed to identify specific ecological factors influencing survival, dispersal, and, ultimately, population abundances aggregated over multiple habitats at regional spatial scales. In this paper, we review several lines of evidence, emphasizing results of our research on paruline warblers in Jamaica, which indicate that migrant passerines often compete intraspecifically in winter for preferred quality habitats and that their populations may be limited at least in part by ecological conditions in winter. The demographic and ecological evidence supporting this hypothesis for migrant passerines includes: (1) differing densities among habitats, suggesting variation in habitat suitability; (2) strong territoriality, site attachment, and site fidelity; (3) experimental demonstrations of habitat saturation; (4) nonrandom distributions of sex and age classes among habitats; (5) overwinter decline of body mass by individuals occupying the most drought—stressed habitats; and (6) different residence times among habitats, suggesting differences in survival or dispersal. We review ecological and behavioral explanations for these demographic patterns, and make conservation recommendations based on our understanding of how local demographic circumstances affect broader scale population processes.
A Fundamental Problem in Key Factor Analysis
Authors: Royama T.
Published: May 2006

This paper reveals that key factor analysis, a popular method of life table analysis, cannot address the central issue of population dynamics: the pattern of population fluctuation and its causal mechanism. The basic idea of key factor analysis is to identify factors that contribute significantly to the variation in population. Several statistical methods to identify a key factor have subsequently been proposed in the literature. These are, in terms of the familiar relationship, K = k1 + k2 +... + kn, to correlate K with a k, regress K on a k, or regress a k on K, the last method being currently most frequently used. These methods, in effect, look for those k's whose variances and covariances constitute a significant part of the variance of K. The fundamental problem here is that the variation in population is inappropriately interpreted as the variance. I show that, in general, different factors play different roles in generating the pattern and that none of these aspects can be indicated merely by the variance of K and its components, the variances and covariances of the k's. I contend that, for judging which factor is major, criteria are multiple and subtle beyond the simplistic idea of key factors.
Role of Biotic Interactions in a Small Mammal Assemblage in Semiarid Chile
Authors: Meserve Peter L. , Gutierrez Julio R. , Yunger John A. , Contreras Luis C. , Jaksic Fabian M.
Published: May 2006

The role of biotic interactions including vertebrate predation and interspecific competition was studied among members of a semiarid small mammal assemblage in a long—term field manipulation in north central Chile. Fences and netting selectively excluded mammalian and avian predators, and a putative rodent competitor, the degu (Octodon degus), from large, replicated grids. Small mammal populations were censused monthly over >4 yr, and effects of predator and degu exclusions on numbers and survival of small mammals were assessed with repeated measures ANOVAs. Marginally significant predator exclusion effects were detected on O. degus, and highly significant year X predation interactions in both wet and dry seasons; degu survival (= persistence) was also significantly longer on exclusion grids. Predation had significant effects on numbers of Phyllotis darwini, and a significant month X predator interaction existed in the wet season; survival was also significantly higher on predator exclusion grids. There was a marginally significant year X competitor interaction in the dry season for this species. Akodon olivaceus had significant month X predator and month X competitor interactions in the wet season only; survival was significantly longer on degu exclusion grids. An irruptive species, Oligoryzomys longicaudatus, showed no significant predator or competitor effects in 1991—1992; however, survival was significantly longer on predator + competitor exclusion (vs. control) grids. An uncommon species, Abrothrix longipilis, had marginally nonsignificant time X competitor interactions but no treatment differences in survival. Finally, a second uncommon rodent, Abrocoma bennetti (not analyzed numerically) had significantly longer survival on predator exclusion grids with degus. Degus and P. darwini were significantly overrepresented (relative to availability) in diets of culpeo foxes (Pseudalopex culpaeus) and three nocturnal owls, respectively, whereas A. bennetti was significantly overrepresented in predator diets generally. Vertebrate predation has pervasive effects on some species that, however, may be related to their intrinsic demographic characteristics. Competition may be mediated by subtle behavioral interactions among assemblage members. Long—term studies are necessary to elucidate the role of biotic and abiotic factors in semiarid environments
Ontogenetic Niche Shifts in Largemouth Bass: Variability and Consequences for First‐Year Growth
Authors: Olson Mark H.
Published: May 2006

The ontogeny of many size—structured organisms is marked by a series of niche shifts that divides a population into ecologically distinct stages. Consequently, overall population dynamics are affected both by processes operating within individual stages and by factors that influence transitions between stages. In largemouth bass (Micropterus salmoides), there is a diet shift from littoral invertebrates to fish that typically occurs sometime in their 1st yr. I examined factors that influenced this shift by tracking diet and growth trajectories of young—of—year (YOY) bass cohorts in several Michigan lakes over 2 yr. Cohorts differed in consumption rates of invertebrate prey, which led to an early divergence in bass growth among lakes. This variation in early growth had dramatic consequences for the timing of the shift to piscivory. In lakes with rapid growth in the invertebrate feeding stage, bass were able to gain a size advantage over YOY bluegill (Lepomis macrochirus), their primary fish prey, which facilitated a shift to piscivory as soon as these bluegill became available as food. In contrast, slow growth during the invertebrate feeding stage reduced the size advantage of bass over bluegill and delayed or even prevented the shift to piscivory in the 1st yr. Niche shifts in bass were also sensitive to environmental conditions early in the growing season. In 1992, low temperatures caused a reduction in growth rates that prevented the establishment of a size advantage over bluegill in all but one lake. Bass grew much faster after switching to piscivory; thus the shift from invertebrates to fish strongly influenced sizes attained by YOY bass by autumn. Because survivorship of YOY bass is strongly size dependent (particularly through the first winter), the timing of the shift to piscivory may be important in determining survival and recruitment rates. Therefore, processes that operate on bass in the invertebrate feeding stage can influence the shift to piscivory, and this can potentially have important effects on the dynamics of the population as a whole.
Ramet Population Dynamics and Net Aerial Primary Productivity of Spartina Alterniflora
Authors: Dai Ting , Wiegert Richard G.
Published: May 2006

Ramet dynamics and net aerial primary productivity (NAPP) were studied in samples of Spartina alterniflora (smooth cordgrass) at Sapelo Island, Georgia. Three populations were compared: tall, short, and short with nitrogen fertilization in spring (short/N). Tall and short S. alterniflora populations had different demographic characteristics. The short population had a shorter leaf longevity (49 vs. 72 d) and a higher leaf turnover than the tall population, which may be due to high salinity and nitrogen limitation in the high marsh. Although the average ramet longevities of tall and short populations were similar (231 and 204 d, respectively), cohorts of the tall population that emerged early in the growing season had a significantly longer average life—span than those of the short population, probably because they had more support from belowground reserves that led to a higher initial survival rate. Leaf number, leaf area, shoot density, and biomass production of the short population were greatly increased by spring nitrogen fertilization, but the longevity of leaves and ramets was little affected. Using the demographic data and phytometric equations (nondestructive method), new growth was found throughout the year in S. alterniflora populations at Sapelo Island. The average dry mass NAPP was estimated to be 1105, 2244, and 1520 g.\mathrm{m}{—2}.\mathrm{yr}{—1}$ for the short, short/N, and tall populations, respectively. Because of its higher leaf turnover, the short population had a higher leaf to stem production ratio than the tall population. NAPP estimates obtained by nondestructive methods usually lie between overestimates and underestimates from harvest methods, indicating that nondestructive methods give accurate estimates of NAPP for salt marshes. Using the highest spring aerial production rates, the upper limits of annual dry mass total production of S. alterniflora at Sapelo Island were calculated as 2555 g/\mathrm{m}2$ for the short population and 4526 g/\mathrm{m}2$ for the tall population. These limits are lower than many previous estimates of annual total primary production for S. alterniflora.
On the Strategy of "Eating Your Competitor": A Mathematical Analysis of Algal Mixotrophy
Authors: Thingstad T. Frede , Havskum Harry , Garde Kristine , Riemann Bo
Published: May 2006

Recent experimental evidence indicates the importance in some pelagic systems of mixotrophic protists that combine photosynthetic ability with the ability to ingest bacteria. If both bacteria and phytoplankton are mineral nutrient limited, this should provide the mixotrophs with the double benefit of combining removal of their competitor with ingestion of the limiting nutrient in pelleted form. It is the objective of this study to expand the classical theories of competition and predation to explore the effect on the microbial food web of one trophic group possessing both strategies. In a chemostat scenario, we analyzed the two—species situation of a mixotroph preying on mineral—nutrient—limited bacteria, and also the situations when the mixotroph in addition has to compete with specialized photoautotrophic and phagotrophic protists, each superior to the mixotroph in their specialized nutritional modes. In the mixotroph—bacteria relationship, somewhat paradoxically, high predatory abilities will reduce the quantitative importance of predation in the mixotroph's nutrition. The reason is a strong reduction in prey abundance, allowing the mixotroph to survive as a photoautotroph despite its low competitive ability. In the three—species case with mixotrophs, bacteria, and specialized phagotrophs, it is shown that the mixotroph can compensate for a "price" paid in reduced affinity for bacterial prey by a sufficiently high affinity for mineral nutrients. In the other three—species case where the mixotroph has to compete with a specialized photoautotroph, the situation is more complex; there is an optimum value for the mixotroph's predatory ability at which mixotroph biomass is maximized. In the general situation with all four species (bacteria, mixotrophs, and specialized auto— and phagotrophs) potentially present, different mixotrophic strategies will alter the equilibrium composition of the consortium, with the mixotroph being most successful with a high affinity for nutrients and an intermediate affinity for bacteria. In the simple form used here, the model predicts no equilibrium with all four species simultaneously present. The theory is in principle directly applicable to laboratory experimentation.
Effects of the Parasite Eimeria Arizonensis on Survival of Deer Mice (Peromyscus Maniculatus)
Authors: Fuller Claire A. , Blaustein Andrew R.
Published: May 2006

Few experimental studies have documented the negative effect of parasites on fitness of hosts under natural or seminatural conditions. We studied the effect of Eimeria arizonensis (Protozoa) on recruitment, winter survival, and change in body mass in deer mice (Peromyscus maniculatus). In field observations, the presence of E. arizonensis was negatively related to recruitment in females and to over—winter survival in males. Experimental manipulation of E. arizonensis in large field enclosures also showed that infection negatively affected over—winter survival of males. There was no relationship between the body mass of deer mice and the presence of either natural or experimental infection. Thus, the mechanism through which E. arizonensis affects survival remains unclear.
Induction of Seaweed Chemical Defenses by Amphipod Grazing
Authors: Cronin Greg , Hay Mark E.
Published: May 2006

Grazing by the generalist amphipod Ampithoe longimana induced increased concentrations of defensive secondary metabolites in the brown alga Dictyota menstrualis and made the seaweed less susceptible to further attack by the amphipod. Although A. longimana preferentially consumes D. menstrualis, its feeding rates can be reduced significantly by high concentrations of diterpenoid dictyols produced by the alga. In 1991, D. menstrualis from sites with high numbers of A. longimana had higher levels of grazing scars, higher concentrations of dictyols, and were less palatable to A. longimana than plants from sites with few amphipods. Among—site differences in palatability to amphipods did not correlate with plant differences in protein, nitrogen, or carbon content. Within a site, plants that had apparent amphipod grazing scars were significantly less palatable to A. longimana than neighboring undamaged plants. Controlled field experiments manipulating A. longimana densities supported the hypothesis that feeding by this amphipod induced elevated chemical defenses in the alga. Compared to undamaged control plants, amphipod—damaged plants had 19—34% more of three diterpenoid secondary metabolites and were 50% less palatable to amphipods. Soluble protein and thallus toughness were unaffected by amphipod grazing and thus could not have caused the differences in palatability. High—pressure liquid chromatography evaluation of adventitious branches growing from blade margins at sites of amphipod grazing scars showed that these branches had significantly elevated levels of two diterpenoids relative to normal blade apices or middles. Thus, the amphipod—induced resistance to further attack occurs through an increase in chemical defenses, and these defenses are, to some extent, localized within the plant thallus. Among—site differences in amphipod densities, grazing scars, seaweed defensive chemistry, and plant palatability that we documented in 1991 varied considerably during 1992 and 1993, suggesting that these interrelationships may be complex. In 1992, A. longimana densities did not differ between sites, and there were no between—site differences in palatability or concentrations of deterrent secondary metabolites. In 1993, however, A. longimana densities did differ between sites, but between—site differences were less dramatic than in 1991. Some secondary metabolites were slightly, but significantly, increased at the site with higher densities of A. longimana, but this had no effect on A. longimana feeding. It has been long recognized that marine herbivores are active participants in seaweed—herbivore interactions and can greatly influence the structure of benthic algal communities. Our findings suggest that seaweeds are not passive participants in these interactions, but can actively alter their susceptibility to herbivores in ecological time. Induced responses to herbivory help explain both spatial (i.e., within—thallus, within—site, and among—site) and temporal variation in the chemical defenses of D. menstrualis.
Interactions Among Gypsy Moths, White‐footed Mice, and Acorns
Authors: Elkinton Joseph S. , Healy William M. , Buonaccorsi John P. , Boettner George H. , Hazzard Anne M. , Smith Harvey R.
Published: May 2006

Low—density populations of gypsy moth, Lymantria dispar, were studied over a 10—yr period in Massachusetts. Increases in gypsy moth density were associated with declines in density of the white—footed mouse, Peromyscus leucopus, a principal predator. Furthermore, changes in density of P. leucopus populations were positively correlated with the density of acorn crops, a dominant winter food source for these mice. To demonstrate these effects we used a novel bootstrap regression method that adjusts for spatial and temporal autocorrelation in the time series data. The findings are compatible with a dual equilibrium model of gypsy moth population dynamics, in which low densities are regulated by mice and high densities are regulated by other factors, notably a virus disease.
Actuarial Senescence and Demographic Heterogeneity in the Florida Scrub Jay
Authors: McDonald David B. , Fitzpatrick John W. , Woolfenden Glen E.
Published: May 2006

Analysis of mortality from a 25—yr sample of 380 Florida Scrub Jays, Aphelocoma c. coerulescens, shows that actuarial senescence (increase in mortality with age) occurs. This refutes the notion that adult mortality is independent of age in birds, and has important implications for evolutionary dynamics. We point to two major factors that may act to mask underlying patterns of actuarial senescence: (1) Selection through time (demographic heterogeneity): because selection inevitably weeds out lower quality individuals first, overall mortality may appear to be constant or even decreasing, despite an increasing force of mortality acting on birds of higher quality. (2) Conflicting processes: one source of mortality may act to decrease mortality over time (e.g., group size effects), while another acts to increase it (e.g., degenerative senescence). Age—specific data, measures of intrinsic quality that are independent of mortality, and exposure of sources of heterogeneity and of conflicting processes allow us to demonstrate a clear pattern of actuarial senescence in an unmanipulated, natural population of long—lived birds. The slow rate of increase in mortality is consistent with the hypothesis that mortality increases more slowly with age in birds than in mammals.
Egg Limitation, Host Quality, and Dynamic Behavior by a Parasitoid in the Field
Authors: Heimpel George E. , Rosenheim Jay A. , Mangel Marc
Published: May 2006

Patterns of host selection and host use by insects with parasitic lifestyles are predicted to be fundamentally dynamic, responding to environmental conditions and physiological states. A particularly robust prediction is that the number of mature eggs that a female carries (her “egg load”) should influence behavior. As egg load decreases, females are predicted to exhibit increasingly selective host use patterns. We tested the hypothesis that egg load and host size influence the behavior of the parasitoid wasp Aphytis aonidiae attacking the armored scale insect Quadraspidiotus perniciosus. Aphytis females can use hosts either for oviposition or for adult “host feeding,” which is the consumption of host material by adult parasitoids. Theory predicts that host feeding should be (i) favored by low egg loads and (ii) more prevalent on lower—quality (smaller) hosts. We conducted observations of individual females foraging freely in the field to determine whether hosts were used for oviposition or for host feeding. As predicted by theory, the likelihood that a host was used for oviposition (as opposed to host feeding) increased with both parasitoid egg load and host size. Thus, parasitoids exhibited higher host—selectivity at lower egg loads. Since egg load and a parasitoid's experience with hosts were not experimentally separated, the egg load effect could in principle have been either direct or indirect and operating through a correlation with experience. In either case, this result constitutes the first demonstration of a link between physiological state and oviposition behavior by a parasitoid in the field. Parasitoid age, as measured using a wing wear index, did not influence behavior. A laboratory study revealed that the relationship between a host's size and the size and initial egg load of the parasitoid developing on that host was positive, but that it followed a pattern of diminishing returns. No effect of host size on behavior could be detected over the range of host sizes that were within the asymptotic region of this relationship.
Male Reproductive Success and Variation in Fruit and Seed Set in Aquilegia Caerulea (Ranunculaceae)
Authors: Brunet Johanne
Published: May 2006

The timing of fruit initiation and the proximity of fruits to resources influence the probability of fruit and seed initiation in many hermaphroditic plants. In two populations of Aquilegia caerulea, both fruit and seed set decreased significanlty between early and late flowers. Low fruit and seed set of late flowers was not due to pollen limitation. Fruit and seed set of late flowers remained low when extra pollen was added to these flowers (pollen quantity), or when all flowers on an inflorescence received self or outcross pollen (pollen quality). While competition for resources occurred among flowers, resource limitation was not responsible for the low fruit and seed set of late flowers. Indeed, preventing pollination of late flowers significantly increased both fruit and seed set of early flowers, but fruit and seed set of late flowers remained low when early flowers were prevented from setting fruits. Late flowers were not just smaller or larger replicates of early flowers, as they allocated more reproductive resources to male function relative to early flowers. Neither herbivory nor architectural constraints could explain the low fruit and seed set of late flowers. While previously published adaptive explanations proposed to explain the low fruit and seed set of late flowers have emphasized a positive aspect to female reproductive success, it is suggested here that both male and female functions should be considered. Morphological data and estimates of male and female reproductive success demonstrate how, both morphologically and functionally, late flowers on inflorescences of A. caerulea specialize as males, early flowers as females. It will be argued that potandry in this sequential bloomer is expected to select for an increase in relative male allocation between early and late flowers, and that the observed pattern of resource allocation and the decrease in fruit and seed set between early and later flowers is consistent with this prediction.
How Many Habitats do Landscapes Contain?
Authors: Knight Thomas W. , Morris Douglas W.
Published: May 2006

The successful integration of theories of habitat selection into landscape ecology depends upon the proper identification of habitat. Habitats must be distinguished at appropriate spatial scales, and evidence must be provided that individuals recognize and respond to the habitat classification. We use evolutionary theories to document how density—dependent habitat selection and habitat variation can be applied to identify habitats in landscapes. We apply our protocol to small—mammal (Clethrionomys gapperi) populations across a series of repeated landscapes in the Hudson Bay Lowland of Ontario, Canada. We postulated initially that the landscapes were composed of two easily distinguishable habitats, but our protocol demonstrated three habitat types influencing density—dependent habitat selection by C. gapperi. The third habitat has profound implications for population regulation in the lowland and highlights the importance of proper habitat identification.
Using Vigilance Behavior to Test Whether Predation Promotes Habitat Partitioning
Authors: Repasky Richard R.
Published: May 2006

Predation could be responsible for habitat partitioning by species if different species are safest from predation in different habitats. Alternatively, predation cannot be responsible for habitat partitioning if all species rank the safety of habitats similarly. I developed predictions to test these two hypotheses, using data on the rates at which animals scan the environment for predators while they forage. Preliminary results suggest that predation is unlikely to be responsible for the habitat preferences of sparrow species wintering along an elevational gradient in the Sonoran Desert of southern California, USA. Two predictions can be tested using vigilance behavior. (1) If species differ in which habitats they are safest from predation, some species will experience increased risk when moved from one habitat to another, whereas other species will experience decreased risk; changes in vigilance levels between habitats will be inconsistent among species. (2) If species are safest in the same habitat, they will experience similar changes in risk between habitats, and should exhibit similar changes in vigilance levels between habitats. Sage Sparrows (Amphispiza belli) and Black—throated Sparrows (A. bilineata) spend the winter in different habitats. I recorded vigilance levels in each habitat while birds foraged on naturally occurring seeds in a portable aviary. Sage Sparrows and Black—throated Sparrows exhibited similar changes in vigilance between habitats, suggesting that these two species are safest in the same habitat, and that predation is unlikely to explain their habitat preferences. Also, I tested and found support for the prediction from vigilance theory that food abundance affects vigilance level. Vigilance declined in response to increased foraging patch profitability, counter to the intuitive prediction that increased food abundance relaxes the threat of starvation, allowing more time for vigilance. This relationship between abundance and vigilance is explained by a simple model of starvation.
Biogeographical and Ecological Correlates of Dioecy in the Hawaiian Flora
Authors: Sakai Ann K. , Wagner Warren L. , Ferguson Diane M. , Herbst Derral R.
Published: May 2006

The angiosperm flora of the Hawaiian Islands, with its high incidence of dioecy, has been central in development of hypotheses about the evolution of dioecy. Based on a recent taxonomic treatment of the Hawaiian angiosperm flora, we analyzed biogeographic patterns of dioecy as well as the association of dioecy with ecological traits potentially important in the evolution of dioecy for native current species and genera. We also analyzed patterns for presumed colonists of the flora to control better for phylogenetic patterns in these traits. Dioecy is associated with woodiness, especially trees; however, this pattern does not hold for gynodioecy. Within woody species, dimorphism (dioecy, gynodioecy, subdioecy, polygamodioecy) is associated with mesic habitats and occurs more frequently in species with lowland and lowland—montane distributions. In contrast, in the endemic Hawaiian Alsinoideae (Schiedea and Alsinidendron) and in Bidens (two groups with autochthonous evolution of dimorphism), dimorphism is associated with more xeric habitats, and for the former group, with wind pollination. For the entire angiosperm flora, dimorphic species are associated with flowers that are small and green. Woody dioecious species and genera are disproportionately associated with wind pollination; hermaphroditic species are disproportionately bird pollinated primarily because of one species—rich lineage in the Campanulaceae. There was no association of dimorphism and pollinator type for colonists. Because of a few species—rich lineages, dimorphism is associated with dry fruits at the specific level, but at the generic level and for colonists, dimorphism is associated with fleshy fruits. Dioecious and gynodioecious species are found more often on older islands, a result of speciation of dimorphic colonists as well as autochthonous evolution of dimorphism. Single—island endemism is not associated with dioecy in the flora as a whole or with dimorphism within lineages evolving dimorphism autochthonously; thus Baker's law is not supported within the Hawaiian Islands. Because the Hawaiian angiosperm flora originated from a minimum of only 291 colonists, many of the associations of dimorphism with ecological traits occur because of the influence of only a few species—rich lineages. Better knowledge of phylogenetic patterns and further ecological studies, particularly within those groups evolving dioecy autochthonously, are needed to determine causality.
Frugivore‐Mediated Selection on Fruit and Seed Size: Birds and St. Lucie's Cherry, Prunus Mahaleb
Authors: Jordano Pedro
Published: May 2006

Frugivorous birds consumed >75% of the ripe fruits of a Prunus mahaleb population in southeastern Spain, but only half of the seed crop was successfully removed from parent plants by legitimate seed dispersers. For two consecutive years, I studied the sign and magnitude of phenotypic selection exerted by frugivorous birds on fruit size and seed mass, two key traits in this mutualistic plant—seed disperser interaction. Individual plants showed extensive phenotypic variation in these traits, but among—individual variation accounted for <30% of total trait variance. Selection patterns were assessed at two levels by separating the effects of selection acting on the parent tree (among—crop selection; comparing fruit removal and seed dispersal efficiency among individual plants) and selection acting at the individual seed level (comparing seed mass variation before and after dispersal by frugivorous birds). Dispersal efficiency (percentage of the seed crop dispersed) correlated negatively with crop size, fruit size, and seed mass. However, only crop size was significantly, positively, correlated with the absolute number of seeds dispersed relative to the population mean, used as the estimator for relative fitness. Greater visitation by dispersers to smaller plants compensated for their lower fecundity but, for plants with larger crops, a greater number of seeds was dispersed despite lower dispersal efficiency. Directional and stabilizing/disruptive selection gradients on fruit traits were not significant or, at best, only marginally significant, indicative of weak and inconsistent selection effects on maternal phenotypes. In contrast, selection on individual seed phenotypes was significant. Seeds on the ground, after successful dispersal by frugivorous birds, were significantly smaller than seeds 'available' at the start of the fruiting season. Observed selection differentials on individual seed mass were —0.12 (1992) and —0.13 (1993), suggesting that frugivores might exert strong selection on individual seed phenotypes irrespective of the maternal phenotype. This selection regime, with far—reaching demographic consequences but low potential for inducing evolutionary change in fruit traits, is expected on the basis of known hierarchical selection cues used by foraging frugivores. Fruit phenotypic variation might be irrelevant as a cue used by birds for discrimination among fruit crops, but, given extensive within—crop variation, frugivores might strongly select among seed phenotypes in a process not related consistently to among—crop selection on maternal phenotypes.
Size and Timing of Metamorphosis in Complex Life Cycles: Time Constraints and Variation
Authors: Rowe Locke , Ludwig Donald
Published: May 2006

Complex life cycles are characterized by niche shifts at the time of metamorphosis. Current models predict optimal sizes for metamorphosis based on maximizing growth, minimizing mortality, or some balance of these goals. These models predict optimal sizes that are independent of the time of metamorphosis. Reproduction and other major events in the life history of organisms are often constrained to seasons, and the state (e.g., mass) of the organism at that time is related to fitness. Therefore, an organism's state as well as the time that that state is achieved are central variables in these time—constrained life histories. We extend earlier theory to include explicit time constraints in three, hypothetical, complex life cycles. Dynamic optimization models are constructed to determine optimal time and mass trajectories for niche shifts. First, we consider the habitat shift at emergence in mayflies, where reproduction terminates a growth period in the first habitat and is constrained to a season. Second, we consider the habitat shift at metamorphosis in amphibians, where reproduction terminates a growth phase in the second habitat and reproduction is constrained to a single point in time. Third, we combine the first two effects to allow an extended period of reproduction in amphibians. Here optimal time and mass trajectories are determined for two niche shifts–the shift from aquatic to terrestrial habitat and the shift from a growth phase to a reproductive phase. We present analytical theory that allows both quantitative and qualitative predictions. Problem constructions and solutions are presented graphically to aid intuition in interpreting our results and extending the framework to other parameter values and other life—history examples. The general conclusion is that time constraints on complex life histories lead to optimal sizes for niche shifts that vary with time. In time—constrained life histories, any variation in the state of individuals at some time prior to reproduction will be preserved to some degree at reproduction. Therefore, in time—constrained life histories, we expect optimal switches in habitat use or life history stage to depend not only on state but also on the time that state is achieved.
Resource Quantity and Offspring Quality in Daphnia
Authors: Tessier Alan J. , Consolatti Nina L.
Published: May 2006

Many species of zooplankton display temporal changes in the size of the offspring they produce. We address the question, is offspring size variation by Daphnia a predictable response to changes in resource abundance? For each of two species of Daphnia (D. pulicaria and D. pulex), we raised several distinct genotypes at each of tree different food levels. Differences in neonate body length, dry mass, and C:N ratio were measured at each food level. The two species responded differently to food level; neonate mass decreased in D. pulex with decreasing food, but the largest (mass) D. pulicaria neonates were produced at the intermediate food level. For both species, the lightest (mass) neonates were produced at the lowest food, but these neonates were often equal (D. pulex), or longer (D. pulicaria) in body length than those produced at high food. The production of small—mass, but relatively large—length neonates in the lowest food level was associated with a lower C:N ratio of both adults and neonates compared with the higher food levels. We conclude that qualitative changes in the production of offspring can result from simple quantitative changes in resource abundance. We suggest that these responses may represent adaptive plasticity in reproduction.
Growth Rate is Negatively Correlated with Hatch Date in Black Brant
Authors: Sedinger James S. , Flint Paul L.
Published: May 2006

Arctic geese nest in a highly seasonal environment in which ungrazed plants reach peak nitrogen concentrations when goslings hatch (Sedinger and Raveling 1986). Grazing by geese prolongs peak nutrient concentrations but reduces food availability. This should cause nutrient availability to decline seasonally. Here, we test the hypothesis that late—hatching goslings of Black Brant (Branta bernicla nigricans) grow more slowly than those hatching early. We substracted the sizes of wild goslings from those of captive—reared goslings of the same age and regressed the differences against hatch date. Differences between wild— and captive—reared goslings for body mass, tarsus length, and culmen length were significantly negatively related to hatch date; i.e., late—hatching wild goslings were smaller than those hatching early, after accounting for age. We detected no between—year difference in gosling size, but male goslings were larger than females of the same age for all measures. Egg size was only weakly associated with size of goslings 1 mo after hatching, but we detected no effect of other brood characteristics on growth. Seasonal variation in gosling growth rate may favor early nesting in arctic geese.
The Size Selection of Clams by African Black Oystercatchers and Kelp Gulls
Authors: Ward David
Published: May 2006

The selction of prey by two species of shore—dwelling birds was compared with the predictions of a simple optimal diet model. The preferences of African Black Oystercatchers (Haaematopus moquini) and Kelp Gulls (Larus dominicanus) for different size classes of the sand—burrowing bivalve Donax serra were examined. Gulls took only large clams, regardless of the availability of the different size classes. This preference is ascribed to the high energy expenditure required for gulls to open clam shells. Oystercatchers, which open bivalve shells relatively easily, took both small and large clams, even when large clams were abundant. The selection of small clams when large clams were abundant appears to have resulted the lack of discrimination of clam sizes by oystercatchers and the temporal segregation of availability of small and large clams.
Large‐Scale Patterns of Forest Succession as Determined by Remote Sensing
Authors: Hall Forrest G. , Botkin Daniel B. , Strebel Donald E. , Woods Kerry D. , Goetz Scott J.
Published: May 2006

The spatial pattern of and the transition rates between forest ecological states were inferred for °260 000 pixel—sized (3600 m2) landscape units using stallite remote sensing. Transition rates were estimated from 1973 to 1983 Landsat images of the study area, classified into ecological states associated with forest succession. The effects of classification error on transition rate estimates were modeled and error adjustments made. Classification of the 1973 and 1983 Landsat images of the 900 km2 study region required a relatively small set of ground—observed and photo—interpreted plots in 1983, with a total area of just 1.62 km2. An innovative technique for correcting multiyear Landsat images for between—image differences in atmospheric effects and sensor calibration, permitted classification of the 1973 Landsat image using 1983 ground observations. Given current Landsat data, and ground observations in one year, this technique would permit monitoring of forest succession and dynamics for nearly a 20—yr period. Results of applying these techniques to a forest ecosystem showed that during the 10—yr observation period it was patchy and dynamic. For both a wilderness and a nonwilderness area in the study region, sizeable values of transition rates were observed and over half of the landscape units were observed to change state: however, a Markov analysis, using the observed transition probabilities, suggests that at the regional level neither the wilderness nor the nonwilderness areal proportions of ecological states are undergoing rapid change.
Bladder Control in Utricularia Macrorhiza: Lake‐Specific Variation in Plant Investment in Carnivory
Authors: Knight Susan E. , Frost Thomas M.
Published: May 2006

Differences among habitats in the relative availability of prey and inorganic nutrients suggest that carnivorous plants should vary their investment in prey capture. We tested this hypothesis using the carnivorous plant Utricularia macrorhiza, which is common in lakes exhibiting a broad range of nutrient conditions. We assessed U. macrorhiza investment in carnivory as the density of prey—capture bladders per leaf. Field surveys revealed that the number of prey—capture bladders per leaf varied significantly among lakes but was highly consistent within a habitat. Differences in the number of bladders reflects an increasing proportion of plant biomass in bladders. Contrary to our initial hypothesis, the number of bladders was positively, not negatively, correlated with the specific conductance of a plant's habitat water. Reciprocal transplant experiments of plants from lakes with many or few bladders per leaf revealed that the number of bladders per leaf is plastic, capable of changing on new leaves over a period of a few weeks. Experimental manipulations of animal prey indicated that a plant's bladder number per leaf is a direct response to water chemistry rather than to prey availability.
Asymmetric Rhodium‐Catalyzed Hydrogenation Meets Gold‐Catalyzed Cyclization: Enantioselective Synthesis of 8‐Hydroxytetrahydroisoquinolines
Authors: Hashmi A. Stephen K. , Haufe Patrick , Schmid Christoph , Rivas Nass Andreas , Frey Wolfgang
Published: May 2006

Different furyl‐substituted (Z)‐dehydroamino acid derivatives were hydrogenated with the rhodium/Mandyphos(OMe)‐system to give enantiomeric excesses between 80 and 98 %. The absolute configuration of the newly formed stereogenic center was determined by anomalous diffraction to be R. These chiral furyl alanines were transferred into 8‐hydroxytetrahydroisoquinolines by employing gold‐catalyzed arene synthesis as the key step. During the latter reaction sequence, also including either a propargylation or a reduction, a protection of the hydroxy group, and a subsequent propargylation, no racemization of the stereogenic center was observed. With very electron‐rich furans, instead of the 8‐hydroxytetrahydroquinolines as products, furans anellated to seven‐membered rings with exocyclic CC double bonds are formed under the same reaction conditions.
Spin‐Density Distribution in the Copper Site of Azurin
Authors: Fittipaldi Maria , Warmerdam Gertrud C. M , de Waal Ellen C. , Canters Gerard W. , Cavazzini Davide , Rossi Gian Luigi , Huber Martina , Groenen Edgar J. J.
Published: May 2006

A 95 GHz pulsed deuterium ENDOR study has been performed on single crystals of azurin from Pseudomonas aeruginosa selectively deuterated at the Cβ position of the copper‐coordinating cysteine 112. Complete hyperfine tensors of the two deuterium atoms have been obtained, which reveal identical isotropic parts. Analysis of the hyperfine tensors provides insight into the spin‐density delocalization over the cysteine ligand. Approximately 45 % of the spin density in the paramagnetic site can be attributed to copper and 30 % to sulfur.
Ab Initio Molecular Dynamics Study of the Keto–Enol Tautomerism of Acetone in Solution
Authors: Cucinotta Clotilde S. , Ruini Alice , Catellani Alessandra , Stirling András
Published: May 2006

We have studied the keto–enol interconversion of acetone to understand the mechanism of tautomerism relevant to numerous organic and biochemical processes. Applying the ab initio metadynamics method, we simulated the keto–enol isomerism both in the gas phase and in the presence of water. For the gas‐phase intramolecular mechanism we show that no other hydrogen‐transfer reactions can compete with the simple keto–enol tautomerism. We obtain an intermolecular mechanism and remarkable participation of water when acetone is solvated by neutral water. The simulations reveal that C deprotonation is the kinetic bottleneck of the keto–enol transformation, in agreement with experimental observations. The most interesting finding is the formation of short H‐bonded chains of water molecules that provide the route for proton transfer from the carbon to the oxygen atom of acetone. The mechanistic picture that emerged from the present study involves proton migration and emphasizes the importance of active solvent participation in tautomeric interconversion.