bluuebunny/crossref_metadata_2025 huggingface dataset:
Parasitoid Response to Concentration of Herbivore Food Plants: Finding and Leaving Plants
Authors: Sheehan William , Shelton A. M.
Published: May 2006

We hypothesized that a parasitoid of an herbivore would be attracted to large rather than small patches of plants that provide food for the herbivore. We conducted experiments to determine whether such parasitoids would be more likely to find and/or less likely to leave large patches of their victims' host plants. We also examined whether prey density (independent of patch size) affects plant finding or leaving. These aspects of plant foraging behavior were examined for Diaeretiella rapae (Hymenoptera: Aphidiidae), a parasitoid wasp that attacks aphids primarily on cruciferous plants. Arrival rates of naturally occurring D. rapae in artificial patches of 5, 10, 20, and 40 potted collard plants were measured in a field experiment. There was no patch—size effect (plants in larger patches were not more likely to be found) and plants with aphids were not more likely to be found than aphid—free plants. Furthermore, there was no dosage response to water bowl traps baited with chemical plant attractant placed in the same field. Leaving rates were measured in a greenhouse experiment using dispersal cages containing 1, 4, or 16 plants and 0, 10, or 100 aphids. Leaving rate decreased in larger patches independently of aphid density, which also affected leaving rate. We conclude that plant leaving may be equally or more important than plant finding in determining abundance of D. rapae in patches of crucifers. The significance of this result is discussed.
Nutrient Budgets and Internal Cycling of N, P, K, Ca, and Mg in Conventional Tillage, No‐Tillage, and Old‐Field Ecosystems on the Georgia Piedmont
Authors: Stinner Benjamin R. , Crossley D. A. , Odum E. P. , Todd R. L.
Published: May 2006

Nutrient budgets (N, P, K, Ca, and Mg) were developed for conventional—tillage, no—tillage, and old—field systems. Data for the budgets were collected over a 2—yr period, with grain sorghum as a main season crop followed by a cover crop of winter rye. Nutrient uptake by crops, weeds, and old—field plants was the largest flow in each system. Leaching losses were small compared to input from fertilizer (except for Ca). Leaching losses of N and Ca was greatest in conventional—tillage, followed by no—tillage systems, and least in the old field. No significant differences were observed between conventional— and no—tillage systems for leaching losses of P, K, and Mg, although leaching of P and K was significantly less in the old field than in either crop system. No—tillage and old—field systems maintained a larger litter component on the soil surface compared to conventional—tillage systems. Decomposition of litter and subsequent mineralization of nutrients appeared to be more rapid in conventional—tillage systems than in either no—tillage or old—field systems. Insect consumers mobilized a small portion of total nutrient flux within each system. In all three systems, nutrients were retained in litter and plant biomass, not lost through leaching.
Patterns of Coexistence in Synaptomys Cooperi and Microtus Pennsylvanicus
Authors: Linzey Alicia V.
Published: May 2006

The microtine rodents Synaptomys cooperi and Microtus pennsylvanicus are sympatric, have a similar life styles, and occur in the same general habitats. The object of this study was to determine the importance of competition in a Microtus—Synaptomys system in southwestern Virginia as a test of the general hypothesis that herbivorous rodents compete directly for space and indirectly for food. The following patterns were observed: (1) Undisturbed populations of Microtus and Synaptomys exhibited microhabitat partitioning when coexisting in heterogeneous habitats that were marginal for Microtus. (2) In the presence of Microtus, Synaptomys microhabitats were characterized by significantly higher densities of deciduous trees and shrubs. (3) Disappearance of Microtus from some habitats during a population decline was accompanied by a shift of Synaptomys into areas formerly occupied by Microtus. Recolonization by Microtus resulted in a return to the previous pattern of microhabitat segregation. (4) Removal of Microtus from an experimental grid was followed by immediate colonization by Synaptomys. (5) One year following removal of Synaptomys from an experimental grid, most of the former Synaptomys habitat remained empty even though Microtus numbers were increasing. (6) Fecal analysis indicated that Synaptomys diet consisted largely of vegetation that is low digestible nutrients (Andropogon in summer, moss in winter). Although Microtus ate Andropogon, this species included more dicotyledons and other monocotyledons in its diet. (7) When Synaptomys was living on a grid from which Microtus had been removed, similarity to food habits of Microtus previously living on the removal grid was much greater than on a grid where the two species coexisted in separate microhabitats (72 vs. 37%). These results suggest that in the southern Appalachians, Synaptomys is excluded from preferred habitats by Microtus and, as a result, lives where cover is sparse and food is low in nutritional value. Although these species do compete, this competition is relaxed when Microtus populations decline. When given access to preferred habitats the food habits of Synaptomys change and resemble those of Microtus, suggesting that the ultimate limiting resource is food. The combination of wider habitat tolerances by Synaptomys and temporal variation in intensity of competition allows coexistence of these species on a regional basis.
Energetics and Growth Rate of Northern Shrike (Lanius Excubitor) Nestlings
Authors: Degen A. Allan , Pinshow Berry , Yosef Reuven , Kam Michael , Nagy Kenneth A.
Published: May 2006

Northern Shrikes (Lanius excubitor) breed in a variety of habitats, including deserts. Deserts are characterized by unpredictable food supplies, which can lead to a slow growth rate of nestlings. However, given that Northern Shrike males use prey from their caches to augment freshly caught prey in providing food for their mates and nestlings, we hypothesized that their nestlings do not have a slow growth rate, but one that is equivalent to that in other passerine nestlings from temperate areas. To test this hypothesis, we measured growth rates and energy use in Northern Shrike nestlings and fledglings. We also measured energy expenditure in two adult males that were attending nests. Growth rate of Northern Shrike nestlings was similar to that predicted for passerines in temperate areas and therefore our hypothesis was supported. However, metabolizable energy available in the cache amounted to only °7.2% of the total energy requirements of the nestlings or 4.2% of the total energy requirements of parents and nestlings during the nestling period. This suggested that other factors in addition to the cache were important in determining growth rate. These include (1) an extremely low maintenance energy require of the nestling; 30% of that predicted for a bird of its body mass when it weighed 10 g, which gradually increased to 70% at 50 g. This allowed for more of the energy intake to be used for growth and also reduced foraging costs of males; (2) the relatively low amount of body energy retained as a fraction of metabolizable energy intake, 0.15 to 0.16, indicating that more water per unit growth was incorporated than in other passerines. Energy expenditure of adult males was substantially lower than that predicted for a passerine of similar body mass. Males collected 4.83 time the energy that they consumed in order to provide their mates and offspring with food. Yet, their ratio of field metabolic rate to basal metabolic rate was only 2.33, the lowest reported value for adults feeding altricial young.
An Exceptional Event of Predation on Desert Snails by Migratory Thrushes in the Negev Desert, Israel
Authors: Shachak Moshe , Safriel Uriel N. , Hunum Richard
Published: May 2006

Migratory thrushes (mostly Turdus philomelos) preyed heavily upon desert land snails, Sphincterochila zonata and Trochoidea seetzenii in Sede Boqer, Israel in late winter, 1972. The event lasted °55 d and occurred only once in 8 yr. Yet due to its low potential for population increase, S. zonata did not recover from the loss of °65% of its population within the 7 subsequent yr. T. seetzenii, on the other hand, recovered rapidly from its loss of 10% of the population. The predation rates as a function of time and of prey densities produced dome—shaped curves. Mostly S. zonata were taken first, but later preferences switched to T. seetzenii. This was associated with a switch in the use of anvils, from stones, which were rare, to the shells of S. zonata, which are thicker than those of T. seetzenii, and were far commoner than stones. Thus the two species differed in the type and density of appropriate anvils on which they could be crackled, and in their density, availability, energy content, and ease of finding and cracking. These differences, associated with the gradual reduction in prey density due to depletion, the acquisition of experience by the birds in locating anvils and prey and in handling them, were responsible for the variation in predation rates and diet composition observed throughout the course of the predation event.
Influence of Biotic Factors in an Upper Intertidal Community: Dipteran Larvae Grazing on Algae
Authors: Robles Carlos D. , Cubit John
Published: May 2006

Field experiments were used to determine the effects of herbivorous fly larvae on ephemeral algae at several rocky beaches in central California. The larvae of marine Diptera form dense populations during seasonal blooms of ephemeral algae in certain higher areas of rocky shores. In three field experiments, changes in the percent cover and species composition of algae on natural and artificial substrates which larvae were allowed to colonize were compared with the changes in algal cover on otherwise similar substrates from which larvae were removed. A system of barriers constructed of copper paint, plastic, iron, and other materials was used to exclude grazing crabs and limpets, which otherwise might have confounded effects produced by the smaller Diptera larvae. In two unreplicated experiments, larval removals caused increases in algal abundance. Statistical analysis of a third, replicated, experiment showed that in certain circumstances the larvae changed the species composition of algal blooms. This effect apparently occurred when grazing hastened species replacements during algal succession. Grazing dipteran larvae are apparently part of a complex association of herbivores that influence algal succession and partially determine the abundances of some high intertidal algae.
Maternal Effects of Temperature on Metabolism in the C_4 Weed Echinochloa Crus‐Galli
Authors: Potvin Catherine , Charest Christiane
Published: May 2006

This study illustrates the physiological and biochemical responses to temperature of maternal phenotypes of plants of Echinochloa acrus—galli that result in different progeny phenotypes. Our results provide a physiological scenario that accounts for strong, nongenetic, maternal effects. At low temperature, the photosynthetic rates of flag leaves were reduced, while concentrations of sugars and starch were increased. These physiological modifications suggest reduced phloem translocation to the reproductive structures in plants grown under cold conditions. At high temperature, high respiration rates of inflorescences were observed during seed development. To offset the effect of ear (fruit) respiration, mother—plants grown under warm conditions would have to translocate some 30% more carbohydrates than at low temperature. Our study therefore suggests that environmentally induced modifications in simple physiological traits can account for an important reduction in resources available to reproduction. Changes in leaf starch, reducing sugars, and protein contents induced by temperature persist through the life of a second generation of plants. Biochemical modifications due to maternal effects may influence overall plant performance. For example, the higher protein concentration of seedlings grown from cold—matured seeds may enhance their cold tolerance.
Lifetime Fitness and Evolution of Reproductive Pattern in the Herbivorous Lady Beetle
Authors: Ohgushi Takayuki
Published: May 2006

The adaptive significance of the timing of oviposition in the thistle—feeding lady beetle Epilachna niponica was investigated at two localities (site A and site F) in the northwestern part of Shiga Prefecture, central Japan. I followed cohorts produced over a season and measured four components of lifetime fitness: egg survival, larval survival, female adult survival from emergence to the reproductive season in the following year, and lifetime fecundity. These data are based on mark—recapture data for >9000 adult beetles and detailed life tables over 5 yr. Large variation in lifetime fitness was evident among cohorts within a population, but the two local populations showed a clear difference in patterns of cohort fitness. At site A, cohorts, produced early in a season had higher lifetime fitness than later cohorts, whereas at site F, later cohorts (except for the last one) tended to have higher lifetime fitness. The major causes of these between—site differences wee seasonal variation in intensity of egg and larval mortalities due to arthropod predation and host plant deterioration. Field observations revealed a significant difference in oviposition phenology between the two sites: early reproduction at site A and delayed reproduction at site F. The relatively longer reproductive life—span of females was responsible for the prolonged reproduction at site F. Results of laboratory experiment that eliminated environmental variables agreed with the field observations, and suggested a genetic basis for the oviposition schedules. Correlation of reproductive pattern at each site with higher lifetime fitness of offspring suggests selection on the timing of oviposition to improve the lifetime reproductive success of females.
When Do Treatment Differences in Movement Behaviors Produce Observable Differences in Long‐Term Displacements?
Authors: Cain Michael L.
Published: May 2006

Movement behaviors are of central importance to the biology of many organisms, and there are many studies that examine the effects of experimental treatments on such movement parameters as the average direction and distance moved. However, thee are few studies that address explicitly the long—term consequences of treatment differences in movement parameters. Instead, it is often assumed that treatment differences in movement parameters will extend, over long periods of time, into treatment differences in long—term, net displacements from a point of origin. I use diffusion models to show that this assumption is not necessarily correct, thus indicating that treatment differences in movement behaviors should be interpreted with caution. In addition, for organisms whose long—term movements can be represented by simple diffusion, I provide formulae that allow calculation of whether treatment effects on movement parameters would be likely to produce treatment differences in long—term displacements. I illustrate these analyses with computer simulations and with data concerning the spread of clonal plants, and I use published values of the diffusion coefficient to help place my results in an ecological context.
Competition Between Aquatic Insects and Vertebrates: Interaction Strength and Higher Order Interactions
Authors: Morin Peter Jay , Lawler Sharon P. , Johnson Elizabeth A.
Published: May 2006

Replicated experiments in artificial ponds demonstrated that an assemblage of aquatic insects competed with tadpoles of the frogs Hyla andersonii and Bufo woodhousei fowleri. We independently manipulated the presence or absence of aquatic insects, and the abundance of an anuran competitor (O or 150 Bufo w. fowleri per experimental pond), using a completely crossed design for two—factor variance analysis, and observed the responses of initially similar cohorts of Hyla andersonii tadpoles to neither, either, or both insect and anuran competitors. Insects and Bufo significantly depressed the mean individual mass at metamorphosis of Hyla froglets and the cumulative biomass of anurans leaving the ponds at metamorphosis. Neither insects nor Bufo affected the survival or larval period of Hyla. Insects also significantly reduced the mean mass of Bufo, showing that both anurans responded to competition from insects. The intensity of competition between natural densities of insects and Hyla tadpoles was comparable to the intensity of competition between Bufo and Hyla, as a density of 150 Bufo/1000 L.
Spatial Variability in a Successional Plant Community: Patterns of Nitrogen Availability
Authors: Robertson G. Philip , Hutson Michael A. , Evans Francis C. , Tiedje James M.
Published: May 2006

We examined the spatial variability of N mineralization, nitrification, and denitrification at a resolution of 1 m over a 0.5—ha portion of an old field in southeast Michigan. Net mineralization and nitrification rates were estimated from changes in ammonium and nitrate during 45—d laboratory incubations of soil from >300 individual sample locations. Denitrification was estimated from nitrous oxide accumulation rates during 24—h incubations of intact cores (n = 252) under acetylene atmospheres at a pressure of 10 kPa. We used geostatistical procedures to characterize the spatial distributions of these and other soil variates. Semivariograms for all three N transformations showed a high degree of spatial dependence among points sampled within 1—40 m of one another. Nugget variances were 27—37% of structural variances, indicating that most of the variation within the sample populations for these rates could be attributed to spatial autocorrelation at a scale >1 m. Isopleths calculated using punctual kriging algorithms show a nonuniform distribution of these transformations across the field. High rates of all processes occurred in swales on the northern edge of the sample area, but also occurred elsewhere in the field on drier, more level sites. These results indicate that spatial characteristics of the measured nitrogen transformations in this old field are complex, and that only some of this complexity is associated with surface topography. Whether spatial complexity affects or mainly reflects plant community structure is not known, but this small—scale heterogeneity may influence existing plant and microbial population dynamics and should be considered by those attempting to understand community dynamics or to quantify ecosystem—level nutrient fluxes.
Predicting Evolutionary Consequences of Greater Reproductive Effort in Tripsacum Dactyloides, a Perennial Grass
Authors: Jackson Laura L. , Dewald Chester L.
Published: May 2006

To test the prediction that a mutation causing greater reproductive effort will result in reduced vegetative vigor, we compared the seed production, growth, and carbohydrate status of normal and pistillate genotypes of the grass Tripsacum dactyloides differing in seed production by up to fourfold. We evaluated the costs of reproduction by two methods: experimental manipulation of reproductive effort and comparison of high and low—yielding genotypes. Despite the large difference in seed production, normal and pistillate (high—yielding) genotypes did not differ in growth rate over a 1—yr period. Contrary to predictions, carbohydrate reserves in the high—yielding genotype were significantly higher at the peak of the seed ripening period. Stalk defoliation and complete removal of seed stalks reduced plant growth rate, total aboveground biomass, and biomass of vegetative storage organs, especially when plants were also under stress from biweekly defoliation. However, stalk removal caused increased rates of growth in the year after experimental manipulations. Reproductive tillers were costly to the plant in terms of lost meristems and therefore future plant size, but seed costs were contained within reproductive tillers of both genotypes, explaining the lack of trade—off in the high—yielding, pistillate genotpye. Although experimental reduction of reproductive effort revealed a cost of reproduction, this result could not be used to correctly predict the consequences of a gene for greater seed production.
Determinants of Recruitment, Juvenile Growth, and Spatial Distribution of a Shallow‐Water Gorgonian
Authors: Gotelli Nicholas J.
Published: May 2006

In the northern Gulf of Mexico, the gorgonian Leptogorgia virgulata (Cnidaria: Octocorallia) recruited onto a shallow limestone outcropping that was covered by sand of various depths. To test the hypothesis that sand limited the recruitment of L. virgulata at this site, I placed cement patio stones as settlement surfaces in different microhabitats. Sand scour reduced recruitment by 50% on buried stones compared with unburied controls. Recruitment was also inhibited by the presence of an algal mat on unburied controls. Initial recruitment patterns persisted for 10 mo on artificial substrata. By that time, dead, intact skeletons were more common on buried than on raised stones. Overall mortality rates did not differ between raised and buried treatments. In a 55—d transplant experiment, buried juvenile colonies grew significantly more than unburied colonies. Rapid growth may enhance survival of buried colonies by raising polyps out of the sand. I mapped the microhabitats in an untouched 24—m2 plot and constructed an index of habitat quality for each contiguous 1—m2 block. This index was highly correlated with numbers of both adult and juvenile Leptogorgia virgulata colonies. Sixty—seven percent of the 1984 recruitment cohort died the following year, but the spatial pattern established at the time of recruitment persisted. Although the abundance of recruits was correlated with habitat quality, there was no relationship between recruitment and adult abundance or the percent cover of encrusting organisms. Finally, recruitment was highest and least variable in patches of clean limestone compared with recruitment in randomly selected patches. On both natural and artificial substrata, the recruitment of Leptogorgia virgulata was affected by the distribution of sand. In spite of heavy 1st—yr mortality, the spatial pattern established at the time of recruitment persisted in the adult population. Mortality after recruitment did not modify the distribution of colonies to any great extent.
Influence of Physiological Integration on Survivorship and Water Relations in a Clonal Herb
Authors: Lau Robyne R. , Young Donald R.
Published: May 2006

To determine the extent of physiological integration in the clonal herb Lycopodium flabelliforme, the survivorship and water relations of severed and connected ramets were compared. In the field, severed ramets experienced 50% greater mortality than intact ramets. In greenhouse experiments, the xylem pressure potentials of severed ramets exposed to 200 μmol°m—2°s—1 of photosynthetically active radiation were as much as 1.3 MPa lower than the xylem pressure potentials of intact illuminated ramets connected to shaded ramets. Thus, a water potential gradient develops within the xylem and facilitates water movement between shaded ramets and connected, illuminated ramets. Measurements of root distribution and capacitance supported this conclusion. Although each ramet did not necessarily have an associated root, water storage was greatest in roots and in ramet crowns, suggesting that irritated ramets lacking nearby roots must rely on other ramets for water. Physiological integration of L. flabelliforme ramets facilitates water movement in the xylem, which may moderate the effects of environmental variability on ramet water potential.
Are Shade Tolerance, Survival, and Growth Linked? Low Light and Nitrogen Effects on Hardwood Seedlings
Authors: Walters Michael B. , Reich Peter B.
Published: May 2006

Variation in shade tolerance is a primary mechanism driving succession in northern deciduous forests. However, little is known about interspecific differences in the traits responsible for shade tolerance. Is shade tolerance due to the ability to grow or survive in deep shade, or both? How do plant morphology and photosynthesis relate to growth in shade? Is low light the sole critical stress determining differences in shade tolerance or do belowground resources interact with low light to affect growth and survival? In this study we address these questions for seedlings of Betula papyrifera Marsh., Betula alleghaniensis Britton, Ostrya virginiana (Mill.) K. Koch, Acer saccharum Marsh., and Quercus rubra L. grown for 2 yr in outdoor shade houses in a complete factorial of low light (2 and 8% open sky) and nitrogen (forest soil and forest soil plus 200 kg N.ha‐1.‐1). For these seedlings we examined effects of light and nitrogen on the interrelationships among survival, growth, and shade tolerance and explored the physiological bases of shade tolerance by examining the relationship of plant morphology and photosynthesis to growth. Nitrogen amendments did not have a significant effect on any plant trait at either light level. In 8% light, growth and survival were highest for shade—intolerant Betula papyrifera and mid—tolerant Betula alleghaniensis, lower for shade—tolerant Ostry and Acer, and lowest for disturbance—adapted Quercus. In 2% light, species rankings reversed as Ostrya and Acer had higher growth and survival than the other species. Second—year survival was strongly related to 1st—yr growth(P <0.001), whereas relationships with 1st—yr plant mass and 1st—yr absolute growth rates were weak. Therefore, survival of shade—tolerant species at 2% light was related to their maintenance of positive growth, whereas intolerant species had growth near zero and high rates of mortality. In both 2 and 8% light photosynthetic rates on mass (but not area) bases and the proportion of the plant in leaves (leaf area ratio and leaf mass ratio) were positively related to growth. Greater rates of growth and survival for shade—tolerant species in very low light, and for intolerant species in higher light, suggest that there is a species—based trade—off between maximizing growth in high light and minimizing the light compensation point for growth. This trade—off may be an important mechanism driving forest community dynamics in northern hardwood forests.
The Evolutionary Role of Indirect Effects in Communities
Authors: Miller Thomas E. , Travis Joseph
Published: May 2006

Indirect effects occurring through chains of direct species interactions have been shown to be important in many communities. If indirect effects have strong ecological effects, then they must also have strong evolutionary effects through natural selection. We consider how indirect effects, both positive and negative, combine with positive and negative direct effects to influence evolution between interacting species. Any one species can evolve in response to direct interactions with other species by changing its “response” to the presence of the other species or changing its “effect” on the species. We argue that the direction (positive or negative) of the direct and indirect effects will determine whether traits related to “response” or “effect” are most likely to be subject to natural selection. Further, covariance patterns of species in the same community should increase when direct and indirect effects between species act in the same direction, resulting in greater compartmentalization of such communities.
Parasitic Plant‐Host Interactions: Plant Performance and Indirect Effects on Parasite‐Feeding Herbivores
Authors: Marvier Michelle A.
Published: May 2006

While the role of parasites in shaping population and community dynamics has been increasingly appreciated, researchers have largely ignored the ecology of parasitic plants. Parasitic plants obtain water, sugar, nitrogen compounds, and a variety of secondary metabolites from their host plants. In a greenhouse study, I examined the direct interactions of a parasitic plant, Castilleja wightii (Scrophulariaceae), with three plant hosts and the indirect effects of this parasitism on the performance of a parasite—feeding herbivore. The three host species, Lupinus arboreus, Artemisia pycnocephala, and Eriophyllum staechadifolium, directly and differentially affected C. wightii flower production, although parasite biomass was not affected by host species. Surprisingly, parasite performance was weakest when attacking a leguminous host, although parasite total nitrogen was highest when growing on a legume. Parasites also exerted a strong direct effect on host performance: host dry mass was negatively correlated with parasite mass for all three host species tested. However, this effect differed among hosts: for E. staechadifolium, proportionately larger parasite mass was correlated with smaller overall biomass of the host and parasite combined, while for the other two hosts, overall host—parasite mass was not correlated with parasite mass, indicating that E. staechadifolium was more affected by parasite attack than were the other host species. Finally, host plant chemistry had strong indirect effects on the performance of an aphid, Nearctaphis kachena, that feeds on C. wightii. Aphids feeding on C. wightii that were parasitizing L. arboreus (alkaloid—producing, high nitrogen), A. pycnocephala (alkaloid—free, intermediate nitrogen), and E. staechadifolium (terpenoid—producing, low nitrogen) experienced 68.2, 65.3, and 49.5% survival, respectively. Further, aphids feeding on parasites using L. arboreus and A. pycnocephala produced 2.43 and 1.77 times more offspring on average than those feeding on parasites using E. staechadifolium. My results indicate that interactions between plant parasites and different host species can have strong direct effects on both host and parasite performance, as well as marked effects on the tritrophic interactions among plant hosts, parasitic plants, and their herbivores.
Nutritional Costs of a Plant Secondary Metabolite Explain Selective Foraging by Ruffed Grouse
Authors: Guglielmo Christopher G. , Karasov William H. , Jakubas Walter J.
Published: May 2006

Plant secondary metabolites (PSMs) are commonly thought to deter vertebrate herbivores by being toxic or by reducing nutrient assimilation. An alternative, complementary hypothesis is that PSMs may influence herbivore forage selection at subtoxic levels by imposing high detoxication costs post absorption. Many studies of insect herbivores have been undertaken to measure the metabolic load of detoxication as it relates to host—plant specialization, but results have been equivocal and the subject of much debate. Some recent studies of vertebrate herbivores indicate that metabolism of PSMs can impose a cost by increasing nutrient losses due to conjugation of PSMs to endogenous materials, and by upsetting pH homeostasis. In this study, we demonstrate that detoxication costs in Ruffed Grouse are substantial, and are reduced by selective foraging. In winter, Ruffed Grouse feed preferentially on quaking aspen with relatively low levels of coniferyl benzoate (CB) in staminate flower buds. We collected aspen buds with low—and high—CB levels and conducted feeding trials with captive Ruffed Grouse that had been acclimated to an aspen bud diet. We measured nutrient utilization efficiencies and excretion of detoxication conjugates. Grouse assimilated 24% less energy from high— vs. low—CB buds. Using a nutritional model, we determined that the reduction of energy utilization efficiency was mainly due to dilution of the diet by CB, and not by digestive inhibition. As CB intake increased, grouse excreted more glucuronic acid and ornithine (two major detoxication conjugates), resulting in an energetic cost of 10% to 14% of metabolizable energy intake for low— and high—CB buds, respectively. Conjugation with the amino acid ornithine increased minimum nitrogen requirement by 68% to 90% for low— and high—CB buds, respectively. Ammonium excretion also increased with CB intake, indicating an upset of pH homeostasis. Thus, detoxication costs were relatively high and increased with higher CB intake. Ruffed Grouse preference for low—CB, high—protein aspen buds in nature appears to be related to lower utilization efficiency and higher detoxication costs associated with high CB concentrations. The importance of detoxication cost to herbivores must be more thoroughly evaluated and integrated into existing models of herbivore foraging behvior.
Annual Variation in Survival and Breeding Probability in Greater Flamingos
Authors: Cezilly Frank , Viallefont Anne , Boy Vincent , Johnson Alan R.
Published: May 2006

Annual local survival of adult Greater Flamingos, Phoenicopterus ruber roseus, breeding at their natal colony in the Camargue (southern France), was studied using ringed birds observed at the colony from 1983 to 1991. Survival and probability of resighting were estimated separately, using capture—recapture models. Because all the birds we observed were nesting, differences in probability of resighting reflect differences in probability of breeding. Winting severity significantly affected survival. Annual local survival was 93% during normal years, but in 1984—1985, following a severe cold spell, survival fell to 76%. Sex and age (range 4 to 14 yr old) had no significant effect on survival. Resightin rates varied between 11% and 88% during the study period. There were significant additive effects of year, sex, and age on resighting. The probability of resighting increased with age in both males and females, reflecting the progressive access to regular reproductive status in this population. However, males had a higher probability of being resighted than females, probably due to their higher rates of mate switching and renesting following breeding failure
Modelling Survival Rates: Habitat Fragmentation and Destruction in Root Vole Experimental Populations
Authors: Johannesen Edda , Ims Rolf A.
Published: May 2006

The effects of habitat destruction and fragmentation on survival rate and population size were tested in an experimental model system consisting of seven enclosed populations of root voles, Microtus oeconomus. The study comprised two consecutive parts. First, the effect of habitat fragmentation was investigated by comparing survival in three populations inhabiting continuous habitat with that in for populations inhabiting fragmented habitat. Second, the continuous habitats were experimentally fragmented by destroying 50% of the area inhabited by the populations, producing the same configuration as in the fragmented habitats. These extensive habitat manipulations were expected to affect survival rates due to changes in the spatiosocial structuring of the populations. Throughout the study, populations were monitored by an intensive live—trapping program. Cormack—Jolly—Sebver methodology was used for statistical modelling and estimation of survival rates. The seven experimental populations differed considerably in population dynamics: some grew, while others remained remarkably stable throughout the experiment. In contrast to expectations, neith population size nor survival rates seemed to be affected by the experimental treatments. survival rate seemed to play a minor role in determining population size. Emigration rates, which also seemed to have little direct demographic importance, were considerably higher in fragmented than in continuous habitats during the first (pre—destruction) part of the study. Surprisingly, this difference persisted after habitat destruction, when all populations experienced the same habitat configuration. We conclude that survival rates in these root vole populations were not dependent on major alterations of spatiosocial structure, possibly owing to adaptation to natural disturbance regimes.
High Survival of Darwin's Finch Hybrids: Effects of Beak Morphology and Diets
Authors: Grant B. Rosemary , Grant Peter R.
Published: May 2006

Three species of Darwin's finches (Geospiza fortis, G. scandens, and G. fuliginosa) hybridize rarely on the small Galapagos island of Daphne Major. Following the exceptionally severe El Nino event of 1982—1983, hybrids survived as well as, and in some cases better than, the parental species during dry seasons of potential food limitation. They also backcrossed to two of the parental species. This study was undertaken to compare the diets of hybrids with the diets of the parental species in order to assess possible reasons for the high hybrid survival. Diets of F hybrids and first generation backcrosses to G. fortis were intermediate between the diets of the respective parental species. Distinctiveness of the hybrid diets was most pronounced where the diets of the parental species differed most. A strong determinant was beak morphology; hybrids inherit beak traits from both parents, and, on average, have intermediate beak sizes. Among the combined groups of species and hybrids, and among the hybrids alone, dietary characteristics covaried with beak morphology. Hybrids that differ most from G. fortis in beak morphology, the G. fortis x G. scandens F hybrids, experience a feeding efficiency advantage when feeding on Opuntia echios seeds, commonly consumed in the dry season. These findings are used to interpret the higher survival of hybrids after 1983 than beforehand. The El Nino event that year led to an enduring (10—yr) change in the habitat and plant composition of the island. A decrease in absolute and relative abundance of large and hard seeds apparently caused relatively high mortality among G. scandens and the largest G. fortis individuals. Hybrids were favored by an abundance of small seeds. The high survival of G. fortis x G. scandens F hybrids may have been due, additionally, to a broad diet and to efficient exploitation of Opuntia seeds. The study demonstrates long—term ecological and evolutionary consequences of large—scale fluctuations in climate, and the role of ecological (food) factors in determining hybrid fitness.
Using Landscape Ecology to Test Hypotheses About Large‐Scale Abundance Patterns in Migratory Birds
Authors: Flather Curtis H. , Sauer John R.
Published: May 2006

The hypothesis that Neotropical migrant birds may be undergoing widespread declines due to land use activities on the breeding grounds has been examined primarily by synthesizing results from local studies. Growing concern for the cumulative influence of land use activities on ecological systems has heightened the need for large—scale studies to complement what has been observed at local scales. We investigated possible landscape effects on Neotropical migrant bird populations for the eastern United States by linking two large—scale inventories designed to monitor breeding—bird abundances and land use patterns. The null hypothesis of no relation between landscape structure and Neotropical migrant abundance was tested by correlating measures of landscape structure with bird abundance, while controlling for the geographic distance among samples. Neotropical migrants as a group were more sensitive to landscape structure than either temperate migrants or permanent residents. Neotropical migrants tended to be more abundant in landscapes with a greater proportion of forest and wetland habitats, fewer edge habitats, larger forest patches, and with forest habitats well dispersed throughout the scene. Permanent residents showed few correlations with landscape structure and temperate migrants were associated with habitat diversity and edge attributes rather than with the amount, size, and dispersion of forest habitats. The association between Neotropical migrant abundance and forest fragmentation differed among physiographic strata, suggesting that landscape context affects observed relations between bird abundance and landscape structure. Finally, associations between landscape structure and temporal trends in Neotropical migrant abundance were counter to those observed in space. Trends in Neotropical migrant abundance were negatively correlated with forest habitats. These results suggest that extrapolation of patterns observed in some landscapes is not likely to hold regionally, and that conservation policies must consider the variation in landscape structure associations observed among different types of bird species and in physiographic strata with varying land use histories.
Complex Effects of Genotype and Environment on Insect Herbivores and Their Enemies
Authors: Stiling Peter , Rossi Anthony M.
Published: May 2006

We performed reciprocal transplants of different Borrichia clones between offshore islands in Pinellas County, Florida, to assess the relative strengths of environment and genotype on the success of the gall midge Asphondylia borrichiae. We measured gall abundance, gall size, gall abortion rate, parasitism rate, stem—tip diameter, nitrogen level, and parasitoid community composition from both experimental and native plants. We found a significant effect of plant clone and environment on all these variables with the exception of gall abortion rate. The effect of environment was usually stronger than that of genotype. This is an unusual result. At sites with higher densities of galls, plants were higher in nitrogen, had bigger stem tips, and produced larger galls. Bigger galls suffered lower parasitism because the smallest species of the parasitoid guild, which is also the most common species, was largely excluded from large galls. The interaction between plant clone and environment was significant for all variables, including abortion rate, which indicates that plant responses, herbivore density, and herbivore mortality are phenotypically plastic. While some authors have found significant interactions between plant genotype and site on herbivore densities, the demonstration of similar phenomena on natural—enemy attack rates and abortion rates of galls is novel, at least for a natural system. In this system, "bottom—up" factors indirectly determine the strength of "top—down" control from parasitoids, by regulating the size of galls.
A Global Trend in Belowground Carbon Allocation: Can We Use the Relationship at Smaller Scales?
Authors: Gower Stith T. , Pongracic Silvia , Landsberg Joe J.
Published: May 2006

We compared independent estimates of total root carbon allocation (TRCA) and fine root net primary production $(NPP_{fr})$ for temperate forests to total root carbon allocation (TRCA—RN) estimates derived from an empirical model developed by J. W. Raich and K. J. Nadelhoffer for world forests. Measured total root carbon allocation for temperate forests ranged from 233 to 1013 g $C\cdot m{—2}\cdot yr{—1}$ and was not correlated to TRCA calculated from the Raich and Nadelhoffer model for world forests. Fine root NPP was not correlated to TRCA—RN; however, a strong correlation was found between $NPP_{fr}$ and TRCA—RN for five control Pinus resinosa natural forests and plantations. The poor correlation between measured TRCA or $NPP_{fr}$ and the estimates may be due to interspecies differences in belowground carbon allocation, variation in foliage: root carbon allocation ratios due to water and nutrient availability, and violations in the carbon budget approach. Using the Raich and Nadelhoffer model to estimate total root carbon allocation and to construct stand carbon budgets for a stand is not an acceptable substitute for measuring soil carbon fluxes.
Ecological Similarity of Shrub‐Desert Avifaunas of Australia and North America
Authors: Wiens John A.
Published: May 2006

The hypothesis that species and communities occupying vegetationally similar environments on different continents should be similar in ecology has become widely accepted, although quantitative support for this hypothesis is meagre. As an indirect assessment of the likelihood of ecological and evolutionary convergence, I quantified features of community structure and of breeding biology, behavior, and life history of birds species occupying several sites in semi—arid shrub deserts in the Great Basin of North America and the interior of Australia. Study sites on both continents were statistically indistinguishable in most quantitative measures of vegetation structure. Breeding—bird assemblages contained the same number of species per unit area, but densities of individuals in Australia averaged half those in North America. A cluster analysis based on a multivariate similarity matrix derived from 14 ecological and life—history characteristics of the species revealed little close matching of Australian species with a North American counterpart, although two such pairings suggest possible ecological convergence. The frequencies of most ecological/life—history traits among species breeding on local plots differed substantially between continents. The Australian species were characterized by longer breeding periods with more breeding attempts, greater social aggregation during breeding and feeding activities, greater use of domed nests, and sedentariness or nomadism rather than seasonal migration. The avifaunas did not differ in mean clutch sizes, the incidence of polygyny, nesting height, territory size, or general dietary patterns. Despite the close matching of vegetation structure on the two continents, differences between the species and communities are more striking than the similarities. These differences may be related to climatic differences between the areas. Although long—term mean precipitation in the Australian and North American shrub—desert regions does not differ, the monthly and yearly variance in Australia is substantially greater. Droughts may be prolonged and widespread, and this factor, together with soil—nutrient limitations, may result in generally lower and more erratic primary and secondary production in the Australian deserts. Close convergence may be lacking because, despite the similarities in habitat structure, the climates and resource levels of Australian and North American shrub deserts differ in fundamental ways, and the avifaunas are of differing phylogenetic derivation. These comparisons emphasize that (1) bird communities are frequently open, so understanding the composition and dynamics of local assemblages requires a broad—scale perspective, and (2) generalizations or explanations developed for one region of the world may not apply in other regions, even if the habitats are similar.
Indirect Herbivore Mediation of Avian Seed Dispersal in Pinyon Pine
Authors: Christensen Kerry M. , Whitham Thomas G.
Published: May 2006

During a 4—yr study, we examined how an insect herbivore indirectly influenced pinyon pine by affecting its avian seed dispersal agents. Colorado pinyon pine, Pinus edulis, suffered reduced cone initiation and increased cone mortality primarily from infestation by the stem— and cone—boring moth Dioryctria albovitella. Because avian dispersal agents selectively foraged where cone crops were highest, individual trees and stands of trees with greater insect abundances were avoided. Even herbivore— resistant trees with substantial cone crops did not receive dispersal services if they were surrounded by susceptible trees because the birds often ignored entire stands of trees. A cone removal experiment showed that avian seed dispersers also ignored trees with artificially reduced crops even though many cones remained. We argue that masting, the production of large cone crops at irregular intervals, may have evolved to insure dispersal success. The decline in attractiveness of entire stands of trees to dispersal agents due to infestation may functionally alter the sex expression of uninfested individuals.