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Mortality Factor (mortality + factor)
Kinds of Mortality Factor Selected AbstractsDemography of the California Condor: Implications for ReestablishmentCONSERVATION BIOLOGY, Issue 4 2000Vicky J. Meretsky The most prominent mortality factor was lead poisoning resulting from ingestion of bullet fragments in carcasses. Successful captive breeding has allowed many birds to be released to the wild since 1992, based originally on an assumption that exposure to lead could be prevented by food subsidy. The mortality of released birds, however, has generally exceeded levels needed for population stability calculated from simple population models. Collision with overhead wires was the most frequent cause of death in releases before 1994. Lead poisoning again surfaced as a problem starting in 1997 as older birds began feeding on carcasses outside the subsidy program. Although poisonings have been treated successfully by chelation therapy in recaptured birds, food subsidy is proving an ineffective solution to lead exposure. The best long-term solution appears to be either the creation of large reserves where hunting is prohibited or the restriction of hunting to nontoxic ammunition in release areas. Until sources of lead contamination are effectively countered, releases cannot be expected to result in viable populations. In addition, problems involving human-oriented behavior have resulted in the permanent removal of many released birds from the wild. The most promising reduction in human-oriented behavior has been achieved in one release of aversively conditioned, parent-reared birds. Rigorous evaluation of the factors reducing attraction to humans and human structures has been hampered by confounding of techniques in releases. Behavioral problems could be more quickly overcome by adoption of a comprehensive experimental approach. Resumen: Las poblaciones silvestres remanentes del cóndor de California (Gymnogyps californianus) de los anõs 80 exhibieron una disminución poblacional rápida debido a altas tasas de mortalidad de individuos adultos e inmaduros. El factor de mortalidad más prominente fue el envenenamiento por plomo ocasionado por la ingestión de fragmentos de municiones en cadáveres. La reproducción exitosa en cautiverio ha permitido muchas liberaciones en ambientes silvestres desde 1992, bajo el argumento de que la exposición al plomo puede ser prevenida mediante el subsidio de alimento. Sin embargo, la mortalidad de aves liberadas ha excedido generalmente los niveles necesarios para alcanzar una estabilidad poblacional calculada a partir de modelos poblacionales simples. Las colisiones con alambres en lo alto fueron la causa más frecuente de las muertes en liberaciones anteriores a 1994. A partir de 1997, el envenenamiento con plomo surgió una vez más como un problema, puesto que las aves de edad avanzada comenzaron a alimentarse de cadáveres fuera del programa de subsidio. A pesar de que el envenenamiento ha sido tratado exitosamente mediante terapia de quelación de las aves recapturadas, el subsidio de alimento ha probado ser una solución ineficaz contra la exposición al plomo. Las mejores soluciones de largo plazo aparentan ser la creación de reservas grandes donde la caza sea prohibida o se restrinja la caza a municiones no tóxicas en las áreas de liberación. Solo una vez que la contaminación por plomo sea contrarrestada efectivamente, no se podrá esperar que las liberaciones resulten en poblaciones viables. Además, los problemas de conductas orientadas hacia humanos ha resultado en la remoción permanente de muchas aves liberadas de zonas silvestres. La reducción más prometedora de conductas orientadas hacia humanos ha sido obtenida en una liberación de aves criadas por sus padres y condicionadas adversamente. La evaluación rigurosa de los factores que reducen la atracción hacia humanos y estructuras de humanos ha sido obstaculizada por la confusión de técnicas en las liberaciones. Los problemas de conducta podrían ser superados más rápidamente mediante la adopción de una estrategia experimental comprensiva. [source] Mortality dynamics and population regulation in Bemisia tabaciENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 2 2005Steven E. Naranjo Abstract Natural mortality is an important determinant of the population dynamics of a species, and an understanding of mortality forces should aid in the development of better management strategies for insect pests. An in situ, observational method was used to construct cohort-based life tables for Bemisia tabaci (Gennadius) Biotype B (Homoptera: Aleyrodidae) over 14 generations on cotton in central Arizona, USA, from 1997 to 1999. In descending order, median marginal rates of mortality were highest for predation, dislodgment, unknown causes, egg inviability, and parasitism. The highest mortality occurred during the 4th nymphal stadium, and the median rate of immature survival over 14 generations was 6.6%. Predation during the 4th nymphal stadium was the primary key factor. Irreplaceable mortality was highest for predation and dislodgment, with the absence of these mortality factors leading to the greatest increases in estimated net reproduction. There was little evidence of direct or delayed density-dependence for any mortality factor. Wind, rainfall, and predator densities were associated with dislodgment, and rates of predation were related to densities of Geocoris spp., Orius tristicolor (White), Chrysoperla carnea s.l. Stephens, and Lygus hesperus Knight. Simulations suggest that immigration and emigration play important roles in site-specific dynamics by explaining departures from observed population trajectories based solely on endogenous reproduction and mortality. By a direct measurement of these mortality factors and indirect evidence of adult movement, we conclude that efficient pest management may be best accomplished by fostering greater mortality during the 4th stadium, largely through a conservation of predators and by managing immigrating adult populations at their sources. [source] Weak parasitoid-mediated apparent competition between two Phyllonorycter (Lepidoptera: Gracillariidae) leaf miner species on a deciduous oak Quercus dentataENTOMOLOGICAL SCIENCE, Issue 3 2009Takashi NAKAMURA Abstract Parasitoid assemblages and the rates of parasitism on tissue-feeding larvae of two Phyllonorycter leaf miner species, P. persimilis and P. leucocorona, were studied from the autumn generation in 2002 to the summer generation in 2005 to understand whether parasitoids mediate interactions between the two leaf miner species. Fourteen species of parasitoids emerged from P. persimilis and 11 emerged from P. leucocorona. The parasitism rate was high: 24.1,92.6% in P. persimilis and 58.9,81.7% in P. leucocorona. Thus, parasitism was a major mortality factor in the present Phyllonorycter species. The parasitoid composition was distinctly different between the two host species, although most parasitoids were able to parasitize both leaf miner species. The analysis based on the quantitative parasitoid overlap revealed that the present parasitoids could mediate interactions between the present leaf miner species, but their effects would be weak. This is attributable to parasitoid's preferential uses of either of the leaf miners as a host. [source] Biology and control of Dicladispa gestroi Chapuis (Col., Chrysomelidae)JOURNAL OF APPLIED ENTOMOLOGY, Issue 9-10 2001V. Delucchi The beetle Dicladispa gestroi is known only from Madagascar, where it is considered to be a pest of rice. Research were carried out from 1885 to 1994 in the Alaotra lake region, the main rice-producing area of the country, characterized by a warm rainy season from October to April and a cool dry season from April to October. The adult beetles invade the rice nurseries and the first direct-seeded fields at the beginning of the rainy season; they have a gregarious behaviour and their feeding activity, together with the mines bored by the larvae, determines a change of colour from green to pale yellow in the damage areas, which resemble outbreak areas of rice leafhoppers. Oviposition takes place only on young rice plants in the tillering stage. Females emerging after the end of February enter a reproductive diapause and leave the rice fields to ,hibernate'. Temperature summations for the egg, larval, and pupal development, as well as for the preoviposition period have been calculated. There is no yield loss up to a larval density of 0.6 per leaf and this economic injury level is seldom exceeded in the Alaotra lake region. Life tables carried out under field conditions show that chalcid parasitoids are the main mortality factor and are responsible for the collapse of entire outbreak areas. Since the discovery of the rice yellow mottle virus in 1989 in the Alaotra lake region and the disease transmission by chrysomelids, the pest status of D. gestroi has changed and control measures have to be applied. However, to avoid interference with the action of the parasitoids, chemical applications should be limited to rice nurseries. [source] Predation by brown trout: a major mortality factor for sexually mature European minnowsJOURNAL OF FISH BIOLOGY, Issue 3 2003J. Museth Brown trout Salmo trutta in the subalpine lake, Øvre Heimdalsvatn, showed large temporal variation in the rate of predation on the introduced minnow Phoxinus phoxinus population. Minnows were found in the stomachs of brown trout between 16 and 38 cm LT. Significantly greater predation was recorded shortly after ice break at the end of June 1999, with frequencies of 9 and 20% within the LT classes 16,29·9 cm and ,30 cm, respectively. Predation on minnows was only occasionally detected during July, August and September. The high level of predation coincided with minnow spawning, and lengths of consumed minnows were equal to those of sexually mature individuals. Accepting a causal link between minnow spawning, which lasted c. 3 weeks, and the contemporary high rate of predation, the estimated annual consumption of minnows by the brown trout population would be 138 kg wet mass. Although most of the annual consumption of minnows by brown trout (90%) occurred within a very short period (3 weeks), it accounted for a significant proportion (60%) of the annual loss in biomass of the sexually mature part of the population. [source] A bioassay for mosquito repellency against Aedes aegypti: method validation and bioactivities of DEET analoguesJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 1 2010Alexander Jahn Abstract Objectives Vector-borne diseases are still a major mortality factor in Africa and South-east Asia and effective mosquito repellents are therefore needed. An efficient and safe in-vitro assay system using artificial blood and skin substitute could facilitate the development of novel repellents, as most assays currently rely on human subjects or vertebrate whole blood. Moreover, examining the skin permeation profiles could provide safer mosquito repellents. The new assay system could serve as an initial system for testing new repellent candidates upon validation with DEET and its analogues. MethodsN,N -Diethyl- meta -toluamide (DEET) and five analogues were synthesised and used to validate a novel in-vitro bioassay using artificial blood and collagen membrane. Repellency against Aedes aegypti was correlated with lipophilicity and skin permeation. Key findings The new in-vitro assay showed good reproducibility (interday relative standard deviation <10% at high concentrations). Four of the five DEET analogues showed repellency similar or superior to that of DEET. Repellency correlated linearly with lipophilicity but stronger repellents tended to permeate skin better. Conclusions The new in-vitro assay using blood substitute and collagen membrane significantly simplifies screening of possible mosquito repellents. Lipophilicity as well as skin permeation profiles should be considered before testing of compounds that are candidates for mosquito repellents. [source] The impact of predation risk from small mustelids on prey populationsMAMMAL REVIEW, Issue 3-4 2000Kai Norrdahl ABSTRACT Small mustelids are ,snake-like' mammals adapted to hunt small rodents, which are their principal prey, in tunnels leaving practically no refuge for the prey. Prey rodents have adaptive behaviours to situations where the predation risk from mustelids is high, including reduced activity and escape by climbing. Small mustelids may affect prey population dynamics directly through killing (increased mortality) and/or indirectly through behavioural changes in prey as a response to the presence of mustelids (predation risk). The Predator-Induced Breeding Suppression hypothesis (PIBS) states that a trade-off between survival and reproduction should lead to delayed breeding under temporarily high predation risk, so that the mere presence of predators may reduce reproductive output. Current results suggest that small mustelids mainly affect prey population growth rate directly through killing. In many cyclic rodent populations, small mustelid predation is a major mortality factor, and experimental evidence supports the hypothesis that these predators drive prolonged summer declines in prey. In contrast, the evidence for PIBS is controversial. Experimental evidence shows that the indirect effects of small mustelids on prey populations are negligible during the best breeding season. However, in other seasons, the presence of predators may indirectly affect prey populations, although this has not been studied experimentally. Prey rodents may decrease mobility as a response to high predation risk by small mustelids, and this reduction in mobility decreases feeding. Reduced feeding affects the energy reserves of voles, and may delay maturation or lower the size of the first litter. [source] Predator, prey and pathogen interactions in introduced snail populationsANIMAL CONSERVATION, Issue 3 2001J. Gerlach The introduction of the carnivorous snail Euglandina rosea to Pacific islands by biological control programmes has had a devastating effect on native snail populations. In most areas the target species, Achatina fulica, has not been affected, although some unsubstantiated reports have led to E. rosea being viewed as an effective control agent. Data from recent laboratory and field studies of E. rosea were combined into a simple model of the interactions between populations of E. rosea and A. fulica and a disease agent. Predictions from the model correspond closely with field data from a number of sites. The model suggests that apparent reductions in A. fulica numbers following E. rosea introduction are the result of a combination of predation and disease effects, and that although the maximum population levels are reduced the population is stabilized at a relatively high level. The model predicts that both A. fulica and E. rosea populations will persist. Partulidae will decline following E. rosea invasion although Samoana spp. may persist at reduced densities. More effective control of A. fulica can be achieved through manual collecting. Control of E. rosea requires the imposition of a significant novel mortality factor. [source] Sea turtle strandings reveal high anthropogenic mortality in Italian watersAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2010Paolo Casale Abstract 1.Spatio-temporal distribution and anthropogenic mortality factors were investigated in loggerhead turtles (Caretta caretta) found stranded or floating in the waters around Italy. A total of 5938 records for the period 1980,2008 were analysed concerning loggerhead turtles measuring from 3.8 to 97,cm curved carapace length (mean: 48.3,cm). 2.Results highlighted the following conservation issues: (i) in the study area, anthropogenic mortality is higher than natural mortality; (ii) interaction with fisheries is by far the most important anthropogenic mortality factor; (iii) longlines are an important mortality factor in the southern areas; (iv) trawlers are the cause of high numbers of dead strandings in the north Adriatic; (v) entanglement in ghost-gear or in other anthropogenic debris affects high numbers of turtles; and (vi) boat strikes are an important source of mortality in most areas but mostly in the warm seasons. 3.Results also indicate that: (vii) the north Adriatic is the area with the highest turtle density; and (viii) the south Adriatic and to a lesser extent the surrounding areas of the north Adriatic and the Ionian, are important developmental areas for loggerhead turtles in the first years of life. 4.Italy is in the centre of the Mediterranean Sea and borders major foraging areas for the loggerhead turtles in the region, and these results confirm previous concerns about the level of anthropogenic mortality in Italian waters. Copyright © 2010 John Wiley & Sons, Ltd. [source] The influence of soil type and moisture on pupal survival of Bactrocera tryoni (Froggatt) (Diptera: Tephritidae)AUSTRALIAN JOURNAL OF ENTOMOLOGY, Issue 1 2006Andrew D Hulthen Abstract, Larvae of the Queensland fruit fly, Bactrocera tryoni, pupate in the soil, but the influence of soil variables on B. tryoni pupal mortality is not known. For other tropical tephritid species, soil moisture has been identified as a major pupal mortality factor. In the laboratory, we tested the effects of soil moisture and soil type on pupal survival through a factorial experiment which used three soil types (loamy sand, loam, sandy clay) and seven soil moisture levels (0%, 10%, 25%, 50%, 75%, 90% and 100%). Minor, but significant, differences in pupal mortality were observed between the soil types, but the most significant factor affecting pupae was extremes of soil moisture. Eighty-five percent pupal mortality occurred at 0% soil moisture and 30% mortality at 100% soil moisture: very low levels of mortality occurred at all intermediate levels. We detected a significant interaction between soil type and moisture level but cannot explain it. In a follow-up experiment, we demonstrated that prepupal wandering larvae of B. tryoni could discriminate between different moisture levels, with significantly greater pupation in loam soil at 75% soil moisture than at either 0% or 100% soil moisture. Results are used to modify a pupal mortality/soil moisture equation used in a recently published DYMEX model of B. tryoni population dynamics. [source] Gall size determines the structure of the Rabdophaga strobiloides host,parasitoid communityECOLOGICAL ENTOMOLOGY, Issue 5 2003Brian H. Van Hezewijk Abstract., 1.,The relationship between gall size and mortality of the willow pinecone gall midge Rabdophaga strobiloides (Diptera: Cecidomyiidae) was examined by determining the fate of all galls in a 30-ha area in central Alberta, Canada over 4 years. It was found that gall size has a large effect on the type and intensity of mortality experienced by the gall midge, and consequently this factor has the potential to influence the dynamics of the host,parasitoid interaction through the creation of phenotypic refuges. 2.,Total midge mortality ranged from 51% to 78% over the course of the study and was dominated by parasitism by Torymus cecidomyiae (Hymenoptera: Torymidae) and Gastrancistrus sp. (Hymenoptera: Pteromalidae) as well as predation by birds. Gall size had a strong, non-linear effect on the attack rates of each of these natural enemies. 3.,Birds attacked the smallest size classes. Torymus cecidomyiae preferentially attacked medium diameter galls and thus avoided predation by birds in smaller galls. Gastrancistrus sp. preferentially attacked the largest galls and consequently suffered lower rates of predation by both T. cecidomyiae and birds. 4.,This study emphasises the importance of understanding the interactions among mortality factors in order to describe adequately the susceptibility of R. strobiloides to parasitism and predation, and ultimately its population dynamics. [source] Mortality dynamics and population regulation in Bemisia tabaciENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 2 2005Steven E. Naranjo Abstract Natural mortality is an important determinant of the population dynamics of a species, and an understanding of mortality forces should aid in the development of better management strategies for insect pests. An in situ, observational method was used to construct cohort-based life tables for Bemisia tabaci (Gennadius) Biotype B (Homoptera: Aleyrodidae) over 14 generations on cotton in central Arizona, USA, from 1997 to 1999. In descending order, median marginal rates of mortality were highest for predation, dislodgment, unknown causes, egg inviability, and parasitism. The highest mortality occurred during the 4th nymphal stadium, and the median rate of immature survival over 14 generations was 6.6%. Predation during the 4th nymphal stadium was the primary key factor. Irreplaceable mortality was highest for predation and dislodgment, with the absence of these mortality factors leading to the greatest increases in estimated net reproduction. There was little evidence of direct or delayed density-dependence for any mortality factor. Wind, rainfall, and predator densities were associated with dislodgment, and rates of predation were related to densities of Geocoris spp., Orius tristicolor (White), Chrysoperla carnea s.l. Stephens, and Lygus hesperus Knight. Simulations suggest that immigration and emigration play important roles in site-specific dynamics by explaining departures from observed population trajectories based solely on endogenous reproduction and mortality. By a direct measurement of these mortality factors and indirect evidence of adult movement, we conclude that efficient pest management may be best accomplished by fostering greater mortality during the 4th stadium, largely through a conservation of predators and by managing immigrating adult populations at their sources. [source] Grazer and virus-induced mortality of bacterioplankton accelerates development of Flectobacillus populations in a freshwater communityENVIRONMENTAL MICROBIOLOGY, Issue 3 2007Karel, imek Summary We present a detailed analysis of the effects of distinct bacterial mortality factors, viral lysis and heterotrophic nanoflagellates (HNF) bacterivory, associated with the development of filamentous Flectobacillus populations. Reservoir bacterioplankton communities were subjected to additions of both HNF and viruses together, or HNF alone, and then incubated in situ in dialyses bags. For distinct bacterial groups, mortality or growth stimulation was analysed by examining bacterial prey ingested in HNF food vacuoles with fluorescence in situ hybridization (FISH) and via FISH with microautoradiography (MAR-FISH). We also developed a semi-quantitative MAR-FISH-based estimation of relative activities of Flectobacillus populations (targeted by the R-FL615 probe). Bacterial groups vulnerable to HNF predation (mainly clusters of Betaproteobacteria), or discriminated against (Actinobacteria), were detected. Bacterial lineages most vulnerable to virus-lysis (mainly the Betaproteobacteria not targeted by the R-BT065 probe, of the Polynucleobacter cluster) were identified by comparing treatments with HNF alone to HNF and viruses together. Filaments affiliated with the Flectobacillus cluster appeared in both treatments, but were about twice as abundant, long and active as in incubations with viruses and HNF as compared with HNF alone. Viruses appeared to selectively suppress several bacterial groups, perhaps enhancing substrate availability thus stimulating growth and activity of filamentous Flectobacillus. [source] Insights from comparative analyses of aging in birds and mammalsAGING CELL, Issue 2 2010Robert E. Ricklefs Summary Many laboratory models used in aging research are inappropriate for understanding senescence in mammals, including humans, because of fundamental differences in life history, maintenance in artificial environments, and selection for early aging and high reproductive rate. Comparative studies of senescence in birds and mammals reveal a broad range in rates of aging among a variety of taxa with similar physiology and patterns of development. These comparisons suggest that senescence is a shared property of all vertebrates with determinate growth, that the rate of senescence has been modified by evolution in response to the potential life span allowed by extrinsic mortality factors, and that most variation among species in the rate of senescence is independent of commonly ascribed causes of aging, such as oxidative damage. Individuals of potentially long-lived species, particularly birds, appear to maintain high condition to near the end of life. Because most individuals in natural populations of such species die of aging-related causes, these populations likely harbor little genetic variation for mechanisms that could extend life further, or these mechanisms are very costly. This, and the apparent evolutionary conservatism in the rate of increase in mortality with age, suggests that variation in the rate of senescence reflects fundamental changes in organism structure, likely associated with the rate of development, rather than physiological or biochemical processes influenced by a few genes. Understanding these evolved differences between long-lived and short-lived organisms would seem to be an essential foundation for designing therapeutic interventions with respect to human aging and longevity. [source] Endectocide residues affect insect attraction to dung from treated cattle: implications for toxicity testsMEDICAL AND VETERINARY ENTOMOLOGY, Issue 4 2007K. D. FLOATE Abstract A 3-year study was performed in southern Alberta, Canada to assess the effect of endectocide residues on the attractiveness of cattle dung to colonizing insects. In 2003 and 2004, insect captures were compared between pitfall traps baited with dung of untreated cattle and paired traps baited with dung of cattle that had been treated 7 days previously with topically applied doramectin, eprinomectin, ivermectin or moxidectin. Faecal residues associated with each compound affected insect captures in both spring and autumn of each year. Effects were detected (P < 0.05) for a total of 94 cases representing 27 insect taxa from 13 families in three orders (Coleoptera, Diptera, Hymenoptera). Two-fold differences in captures were common. Up to six-fold differences were observed. Eleven cases of attraction and 11 cases of repellency were associated with residues of doramectin. Eprinomectin tended to repel insects, with decreased captures for 19 of 29 cases of effect. Ivermectin showed a strong attractive effect, with increased captures for 17 of 25 cases. Moxidectin also showed a strong attractive effect, with increased captures for 17 of 18 cases. Comparisons between compounds suggested that results for doramectin best predicted results for eprinomectin and vice versa. In 2005, insect captures were compared between pitfall traps baited with dung of untreated cattle and traps baited with dung from cattle treated 3, 7 or 14 days previously with topically applied doramectin. Effects were detected in 14 cases plus one case of near significance (P= 0.053). Significant differences between control vs. days 3, 7 and/or 14 dung were detected in nine cases. Residues enhanced captures in seven of these cases. Day 14 dung affected captures in six of these cases. This study shows that endectocide residues can affect the number of insects attracted to colonize and oviposit in dung. Hence, the emergence of their offspring from field-colonized dung of untreated vs. endectocide-treated cattle should not be used as a measure of residue toxicity per se, but rather as a measure of ,insect activity'. Insect activity is a composite measure of residue toxicity, the number and species composition of insect colonists, and the mortality factors (e.g. predation, parasitism, competition) associated with the co-occurrence of these species in the dung pat. [source] Sea turtle strandings reveal high anthropogenic mortality in Italian watersAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2010Paolo Casale Abstract 1.Spatio-temporal distribution and anthropogenic mortality factors were investigated in loggerhead turtles (Caretta caretta) found stranded or floating in the waters around Italy. A total of 5938 records for the period 1980,2008 were analysed concerning loggerhead turtles measuring from 3.8 to 97,cm curved carapace length (mean: 48.3,cm). 2.Results highlighted the following conservation issues: (i) in the study area, anthropogenic mortality is higher than natural mortality; (ii) interaction with fisheries is by far the most important anthropogenic mortality factor; (iii) longlines are an important mortality factor in the southern areas; (iv) trawlers are the cause of high numbers of dead strandings in the north Adriatic; (v) entanglement in ghost-gear or in other anthropogenic debris affects high numbers of turtles; and (vi) boat strikes are an important source of mortality in most areas but mostly in the warm seasons. 3.Results also indicate that: (vii) the north Adriatic is the area with the highest turtle density; and (viii) the south Adriatic and to a lesser extent the surrounding areas of the north Adriatic and the Ionian, are important developmental areas for loggerhead turtles in the first years of life. 4.Italy is in the centre of the Mediterranean Sea and borders major foraging areas for the loggerhead turtles in the region, and these results confirm previous concerns about the level of anthropogenic mortality in Italian waters. Copyright © 2010 John Wiley & Sons, Ltd. [source] Host plant effects on the development and survivorship of the galling insect Neopelma baccharidis (Homoptera: Psyllidae)AUSTRAL ECOLOGY, Issue 3 2002M. M. Espírito-Santo Abstract In this study, the mortality factors acting upon the galling psyllid Neopelma baccharidis Burckhardt (Homoptera) caused by its host plant, Baccharis dracunculifolia De Candole (Asteraceae) were analysed. In March 1999, 982 galls of the same cohort were randomly marked on 109 individuals of B. dracunculifolia in the field. Galls were censused each month during their development, from April to August, and dead galls were collected and analysed for mortality factors. Gall dehiscence rates were calculated for each month. The major mortality source of N. baccharidis was gall dropping (13.2% of the original cohort), which is probably a normal outcome of previous mortality caused by the other factors observed in this study. Unknown factors killed 11.7% of this gall population and were ascribed to plant resistance during gall development. Empty galls represented 7.7% of the observed mortality and may be a consequence of egg retention or egg mortality/abortion related to variations in plant quality. Shoot mortality was high during the dry season and killed 7.5% of the galls, but this impact was minimized after the third month from gall formation due to the ability of nymphs to accelerate development and emerge from galls on dying shoots. However, the size of dehisced galls on dead shoots tended to be smaller, possibly affecting adult performance. Mortality of N. baccharidis attributed to B. dracunculifolia strongly controlled the galling insect population, killing 40.7% of the original cohort of galls. Plant-mediated mortality was caused by often neglected factors acting predominantly during the first 3 months of development, which are critical to gall survivorship. These results reinforce the importance of bottom-up forces in plant-insect systems. [source] Postdispersal Seed Fate of Tropical Montane Trees in an Agricultural Landscape, Southern Costa RicaBIOTROPICA, Issue 3 2009Rebecca J. Cole ABSTRACT Variation in postdispersal seed fate is an important factor driving patterns of forest regeneration. Because most previous studies have not tracked final seed fate and have commonly equated seed removal with predation without considering the possibility of secondary dispersal, little is known about individual seed mortality factors in successional and degraded habitats. This study tracked the postdispersal fate of large-seeded tropical montane trees in abandoned pasture, young secondary forests, and small forest fragments during two consecutive years in an agricultural landscape in southern Costa Rica. The incidence of secondary dispersal by animals, scatterhoarding in particular, and the effects of seed burial on germination were measured. Overall, seeds survived through germination more often in secondary forests with high levels of mortality occurring in abandoned pastures and forest fragments. The majority of seed mortality was caused by rodent predation in forest fragments, insects and fungal pathogens in secondary forests, and a combination of desiccation, insects, and fungal pathogens in pastures. Seeds were frequently secondarily dispersed in larger forest fragments, whereas they were only rarely moved in pastures and secondary forests. Burial tended to improve germination in pastures and was important for an often scatterhoarded species, Otoba novogranatensis, in all habitats. The results of this study suggest that: (1) seed mortality factors differ in response to the type of habitat degradation; (2) large-seeded species have high potential for survival when dispersed to young secondary forests; and (3) seed removal is not a reliable proxy for seed predation, particularly in less degraded forest fragments. RESUMEN La variación en el destino de las semillas posterior a la dispersión es un factor importante que puede determinar patrones de la regeneración de los bosques. Dado que la mayoría de los estudios anteriores no han realizado seguimiento al destino final de las semillas y han equiparado comúnmente la remoción con la predación sobre las mismas, sin tener en cuenta la posibilidad de dispersión secundaria, poco se sabe sobre los factores de la mortalidad de semillas en hábitats sucesionales y degradados. Este estudio hizo seguimiento al destino posterior a la dispersión de semillas grandes de árboles tropicales montanos en pasturas abandonadas, bosques secundarios jóvenes y en pequeños fragmentos de bosque durante dos años consecutivos en un paisaje agrícola del sur de Costa Rica. Se midieron la incidencia de la dispersión secundaria por parte de los animales, particularmente por scatterhoarding (estrategia en la cual se almacenan pequeñas cantidades de alimento en distintos escondites), así como los efectos que tiene el entierro de semillas sobre la germinación. En general, las semillas sobrevivieron hasta la germinación con más frecuencia en los bosques secundarios, teniendo altos niveles de mortalidad en las pasturas abandonadas y en los fragmentos de bosque. Gran parte de la mortalidad de semillas fue causada por la predación de roedores en fragmentos de bosque, de insectos y hongos patógenos en los bosques secundarios, y de una combinación de desecación, insectos y hongos patógenos en los pastos. Las semillas presentaron una frecuente dispersión secundaria en los fragmentos de bosque más grandes, mientras que sólo en raras ocasiones se trasladaron en los pastos y los bosques secundarios. El entierro de semillas mostró tendencia a mejorar la germinación en los pastos y fue importante para Otoba novogranatensis, especie cuyas semillas son en ocasiones dispersadas por scatterhoarding en todos los hábitats. Los resultados de este estudio sugieren que (1) los factores de mortalidad de semillas difieren en respuesta al tipo de degradación del hábitat, (2) las especies con semillas de gran tamaño tienen un alto potencial de supervivencia cuando se dispersan a bosques secundarios jóvenes, y (3) la remoción de semillas no es un indicador confiable de la predación sobre las mismas, particularmente en fragmentos de bosques menos degradados. [source] | ||||||||||||||||||||||