The dynamics of buried weed seeds in ridge-tilled corn (Zea mays L.) and soybeans [Glycine max (L.) Merr.] were studied in Minnesota. Soils subjected to continuous corn production harbored at least twice as many buried weed seeds as soils under corn/soybean rotations. Truncation of ridges at the time of crop sowing removed 31 to 37% of the buried weed seeds from ridges of continuous corn, and 80 to 100% of those from ridges of the corn/soybean rotations. From 14 to 36% of weed seeds originally in ridges were lost through germination either on the ridge or in the furrow. Ridging soil at layby stimulated germination of numerous weed seeds. The resulting population of small weeds eventually produced up to 1000 seeds/m2 in continuous corn but only about 100 seeds/m2 in corn/soybean rotations, thoroughly replenishing the soil seed reserve in both cropping systems. After 7 to 8 yr of good to excellent weed control with herbicides, crop yield losses in the absence of herbicides were 10 to 27% in continuous corn, and 0% for corn and 6 to 10% for soybeans in corn/soybean rotations.

Knowledge of weed biology is essential for development of both economically and environmentally acceptable weed management systems. Weed biology relates to plant attributes such as morphology, seed dormancy and germination, physiology of growth, competitive ability, and reproductive biology. Concepts of population biology such as seedbank dynamics for annuals and root reserves, dormancy, and longevity of vegetative propagules for perennials can be used to predict weed infestations better and to evaluate sustainable management strategies. Integrated approaches that give priority to depletion of root reserves or seedbanks through interfering with dormancy or germination requirements have great potential to enhance weed management strategies in the future.

Weed-suppressive soils contain naturally occurring microorganisms that suppress a weed by inhibiting its growth, development, and reproductive potential. Increased knowledge of microbe–weed interactions in such soils could lead to the identification of management practices that create or enhance soil suppressiveness to weeds. Velvetleaf death and growth suppression was observed in a research field (fieldA) that was planted with high populations of velvetleaf, which may have developed via microbial mediated plant–soil feedback. Greenhouse studies were conducted with soil collected from fieldA (soilA) to determine if it was biologically suppressive to velvetleaf. In one study, mortality of velvetleaf grown for 8 wk in soilA was greatest (86%) and biomass was smallest (0.3 g plant−1) in comparison to soils collected from surrounding fields with similar structure and nutrient content, indicating that suppressiveness of soilA was not likely caused by physical or chemical factors. When soilA was autoclaved in another study, mortality of velvetleaf plants in the heat-treated soil was reduced to 4% compared to 55% for the untreated soil, thus suggesting that suppressiveness of soilA is biological in nature. A third set of experiments showed that suppressiveness to velvetleaf could be transferred to an autoclaved soil by amending the autoclaved soil with untreated soilA; this provided additional evidence for a biological basis for the effects of soilA. The suppressive condition in these greenhouse experiments was associated with high soil populations of fusaria. Fusarium lateritium was the most frequently isolated fungus from roots of diseased velvetleaf plants collected from fieldA, and also was the most virulent when inoculated onto velvetleaf seedlings. Results of this research indicate that velvetleaf suppression can occur naturally in the field and that F. lateritium is an important cause of velvetleaf mortality in fieldA.

Age distributions of sulfur cinquefoil populations were determined on sites that were historically grazed, cultivated, and mechanically disturbed. From 12 sites, a total of 279 reproductively active plants were collected and aged by using herbchronology (counting rings in the secondary root xylem of the root crown) to (1) estimate the age structure of the populations, (2) relate plant size and flower production to plant age, and (3) examine the relation of population age structure to environmental variables and disturbance history. Results indicated that the mean age for all sampled plants was 3.5 (± 1.74 SD) yr and ranged from 1 to 10 yr. Age was not related to number of flowers, plant size (number of stems per plant or plant height), or site disturbance type but was positively correlated with site elevation (P < 0.001). The pooled age distribution from all 12 sites was right-skewed with fewer old plants than young plants. We conclude that sulfur cinquefoil plants sampled in northeast Oregon are able to colonize, establish, and reproduce at disturbed sites rapidly. We suggest that herbchronology may be a useful technique to improve understanding of invasion biology and ecology for invasive plant species that form annual rings.

Life history accounts for the chance of survival and reproductive success of a species, considering, for example, when, how often and how much a species reproduces. Consequently, it is directly related to the success or failure of bioinvasions. Here, we investigated some aspects of the life history of the cryptogenic calcareous sponge Sycettusa hastifera. A population from Arraial do Cabo, Brazil (south-western Atlantic) was investigated from September 2008 to December 2009 by monthly collections and histological analyses. We observed that S. hastifera reproduced continuously throughout the year without seasonality and presented high fecundity. The fecundity was not different depending on the sponge body part (top or base), but it was related to the wet weight of the sponge (although a minimum size was not required for reproduction). Reproduction could not be predicted by the seawater temperature. The reproductive characteristics of S. hastifera were similar to those of other previously studied calcareous sponges. Sycettusa hastifera shows traits of an invasive species, such as high fecundity, short life cycle, early sexual maturity and the ability to use pioneer habitats. Consequently, it possesses several characteristics that would allow it to invade new areas.

Ninety-five percent of orchid species associated with fynbos shrublands of South Africa's Cape Floristic Kingdom have been assessed for the IUCN Red List, yet aspects of their demography and population biology remain poorly understood. We conducted a 6-year demographic study of the Critically Endangered Disa procera, a cryptic, terrestrial species from South Africa with a global population of c. 50 individuals known from a single location. We aimed to provide management recommendations that would facilitate its persistence. Our findings indicate that the population of D. procera is larger than previously thought, and the species occurs at two distinct locations. These orchids exhibit high interannual variation in population size and turnover of individuals, potentially indicative of a species with a short life span, and still meet the criteria for Critically Endangered status. The species benefits from disturbances, such as brush cutting along trails, or fire, which open up clearances in the vegetation. However, physical damage to plants during their aboveground growing season (September–January) is particularly detrimental and should be avoided in habitat management for the species. Fire had beneficial effects at the population and individual levels and is recommended at 10–25-year intervals, outside the orchid's growing season. The species exhibited comparatively high rates of fruit set (68%), suggesting that pollination limitation does not currently constrain its performance. Its patchy distribution may, however, indicate constraints on dispersal or recruitment. We recommend that management strategies should include continued protection and monitoring of both populations, studies on pollination, habitat requirements and mycorrhizal associates, and a prescribed disturbance regime.

Sampling of the demersal ichthyofauna of Guanabara Bay was conducted bimonthly for 2 years at 10 stations distributed along a hydrobiological gradient. A total of 16,081 Tetraodontiformes specimens were collected, representing 10 species distributed among Ostraciidae, Monacanthidae, Tetraodontidae and Diodontidae. Tetraodontiformes appear to be well adapted to hydrological variations and inhospitable conditions prompted by intense eutrophication. However, abiotic factors traditionally considered important in estuarine community structure play a secondary role in the distribution of Tetraodontiformes. The type of sediment appears to be the most important physical factor but acts only as an indicator of ecological domain. The low explanatory power of physicochemical variables, in addition to the relative stability of the bay's ichthyofauna, suggests an influence of biological parameters. The species exhibited wide variation in their use of Guanabara Bay and utilized it as a resting, feeding and growing area. Among the species captured, Stephanolepis hispidus, Lagocephalus laevigatus, Sphoeroides greeleyi, Sphoeroides testudineus, Sphoeroides tyleri, Chilomycterus reticulatus and Chilomycterus spinosus were categorized as marine estuarine opportunists, and Aluterus heudelotii and Aluterus schoepfii were classified as marine stragglers. Acanthostracion sp. could not be categorized. The boom of C. spinosus indicates an ecological misbalance and must be carefully investigated.

Tropical forest insects are vertically stratified between the canopy and understorey. Using 60 traps set at two heights above the forest floor (30 at 15 cm and 30 at 1 m) we compared abundances in capture height, persistence in traps, and sex of three co-occurring understorey butterflies (Cithaerias pireta, Dulcedo polita and Pierella helvina) in Costa Rica. We captured, marked and released 283 individual butterflies (65 C. pireta, 79 D. polita, 139 P. helvina) and showed all three species were captured more often in low traps, and P. helvina was captured only in low traps. The probability of remaining in traps for 24 h did not differ significantly for D. polita and P. helvina, but was significantly lower for C. pireta. The odds of trapping either sex did not differ significantly for P. helvina and C. pireta, but they were significantly lower for D. polita males. We experimentally demonstrate that these co-occurring species fly and feed just above the forest floor, but differ with respect to their persistence in traps and attraction to traps by sex. Our study implies that closely related species can exhibit behavioural differences that may influence population abundance estimates in multi-species studies.

Echinoderms are well represented in nearshore hard-bottom (< 100 m depth) habitats along the Antarctic Peninsula where they are presumably important contributors to benthic production, carbon flow, and determinants of community structure. The present study assesses the densities of echinoderms at shallow depths (2–15 m) at five sampling sites within three kilometres of Anvers Island on the central western Antarctic Peninsula. The asteroids Odontaster validus, Granaster nutrix, Lysasterias perrieri and Adelasterias papillosa, two ophiuroids in the Amphiuridae, the holothuroids Psolicrux coatsi and Psolus carolineae and one representative of the Cucumaridae, and the regular echinoid Sterechinus neumayeri were enumerated. Mean total echinoderm densities were high (34.9 individuals m-2) and ranged from 21.9 individuals m-2 for asteroids to 2.7 individuals m-2 for holothuroids. With the exception of a positive relationship between the abundance of the regular echinoid Sterechinus neumayeri and the biomass of the brown alga Himanthothallus grandifolius, no significant relationships were found between the abundance of asteroids, ophiuroids, or holothuroids and two species of brown algae or three algal ecotypes. The present study indicates nearshore hard-bottom echinoderms are important in the carbon cycle and their inherent vulnerability to ocean acidification may have community-level impacts.

The fiddler crab Uca (Minuca) victoriana von Hagen, 1987 has been reported, until recently, only from the type locality at Vitória, State of Espírito Santo, Brazil. We report here, for the first time, the occurrence of U. (M.) victoriana in estuaries of the States of Bahia and Pernambuco, north-eastern Brazil, extending its distribution; as well as some aspects of its population biology. For the population study, four sites were defined in mangroves of the Mamucabas and Ariquindá Rivers, Pernambuco, on different types of substrate, and sampled monthly during spring low tide from April 2008 through to March 2009. A total of 41 specimens were obtained in June 2008 in the Arinquindá River, of which 25 were males, 16 non-ovigerous females and 1 ovigerous female. In the Mamucabas River, 772 crabs were collected over the year, including 472 males, 300 non-ovigerous females and 2 ovigerous females. In both areas, the U. (M.) victoriana population showed a unimodal size–frequency distribution, with males and females (ovigerous and non-ovigerous) similar in size (7.46 ± 1.60 mm for males and 7.09 ± 1.45 mm for females; t = −0.744; P > 0.05). The overall sex-ratio (1:1.57) differed significantly from the expected 1:1 proportion1 (χ2 = 38.32; P < 0.05). Study of material deposited in Brazilian carcinological collections revealed several misidentified specimens, especially as U. (M.) rapax and U. (M.) burgersi. Some morphological characters to distinguish among these species are presented.

We present a general framework for analyzing the contribution to reproductive success of a behavioural action. An action may make a direct contribution to reproductive success, but even in the absence of a direct contribution it may make an indirect contribution by changing the animal's state. We consider actions over a period of time, and define a reward function that characterizes the relationship between the animal's state at the end of the period and its future reproductive success. Working back from the end of the period using dynamic programming, the optimal action as a function of state and time can be found. The procedure also yields a measure of the cost, in terms of future reproductive success, of a suboptimal action. These costs provide us with a common currency for comparing activities such as eating and drinking, or eating and hiding from predators. The costs also give an indication of the robustness of the conclusions that can be drawn from a model. We review how our framework can be used to analyze optimal foraging decisions in a stochastic environment. We also discuss the modelling of optimal daily routines and provide an illustration based on singing to attract a mate. We use the model to investigate the features that can produce a dawn song burst in birds. State is defined very broadly so that it includes the information an animal has about its environment. Thus, exploration and learning can be included within the framework.

The population dynamics and reproduction of the hermit crab Clibanarius vittatus were evaluated on Pescadores Beach, located on the estuarine channel of São Vicente (São Paulo), Brazil. The hermit crabs were captured by hand during low tide, from May 2001 to April 2003. A total of 2554 hermit crabs were captured, of which 701 were males, 1741 non-ovigerous females, 48 ovigerous females and 64 intersex individuals. The size–frequency distribution of the males was represented by a platykurtic bell-shaped curve, which differed from the leptokurtic bell-shaped curve of the females. The smaller and intermediate classes were composed mainly of females (modal size 6.5–7.5 mm carapace shield length (CSL)), and the larger classes only by males (modal size 9.5–10.5 mm CSL). The overall sex-ratio was skewed toward females (0.39:1/M:F), differing significantly from the expected 1:1. A seasonal reproductive pattern was recorded for C. vittatus in this location, with more intensive reproductive activity in the warmer months. The absence of juveniles suggests that their recruitment area is different than the area inhabited by adults, possibly another area with more protection and specialized or different resources for young.

Experimental studies were conducted on the proportion of Steinernema feltiae Filipjev (Site 76 strain) infective stages that infected Galleria mellonella L larvae, in sand tube assays. A full statistical analysis of the sand assay tubes was also undertaken. The analysis showed that the sand tubes were not a significant source of variation. Consequently the observed behaviour of the infective stages was considered to be due to a biological effect. The study shows that the proportion of infective stages that became parasitic did not increase with increases in the density of applied infective stages, nor did the proportion increase with an increase in the number of hosts. It is argued that these findings are consistent with the presence of a proportion of individual infective stages that are capable of causing infection.

To assess ectoparasite impact on individuals and populations of Gerbillus andersoni allenbyi under natural conditions, I addressed the following questions. Do ectoparasites affect their host fitness and, if so, how? Do ectoparasites affect host population level? Does this parasite–host interaction support the traditional concept of parasite evolution towards avirulence? For this purpose, host infestation, infection, survival, haematological indices, and physical condition were recorded. A field experiment which included manipulating host infestation while recording host survival was conducted to determine the causal relations between these variables. G. a. allenbyi was infested by 2 fleas (Synosternus cleopatrae and Stenoponia tripectinata), 5 mesostigmatid mites (Androlaelaps centrocarpus, A. hirsti, A. insculptus, A. marshalli and Hirstionyssus carticulatus), 1 tick (Rhipicephalus sanguineus), and 1 louse (Polyplax gerbilli). Ectoparasite burden significantly reduced host survival and red blood cell indices (red cell concentration, haemoglobin concentration and haematocrit). Ectoparasite burden did not significantly affect white blood cell concentration. Gerbils were not infected by haemoparasites or gut helminths which potentially could cause anaemia. The causal relationship between S. cleopatrae burden and host survival was established by manipulation of host infestation. Both ectoparasite removal and initial level of infestation significantly affected host survival. Ectoparasites that caused anaemia were not associated with host physical condition (PC), measured as weight/length3. None of the red blood cell indices was correlated with host PC. These results suggest both that host PC was not affected by ectoparasite burden and that exsanguination leading to anaemia was the main effect of the ectoparasites. Ectoparasite pressure on the host population (based on the ectoparasite effects as estimated by statistical models, combined with dispersion of the infestation within the host population) changed seasonally and was greatest when host density was the highest. A large segment of the gerbil population was affected by ectoparasites during the entire year. An explanation for the evolution of parasite virulence, contrasting parasites that evolve towards increased virulence with parasites that evolve towards avirulence is presented. This classification is primarily based on whether parasite impact is equated with a higher efficiency of host exploitation, or whether it is a ‘side effect’ of parasite biology.

The relationship between host dietary protein and intestinal helminth population biology during primary infection was studied using a mouse–T. muris experimental model. Uninfected CBA/Ca mice fed either a 4% (by mass) or 16% protein diet grew at a similar rate, but both suffered significant growth retardation when infected with T. muris. T. muris initial establishment and fecundity were unaffected by dietary protein content, but were significantly influenced by infection dose, declining at the higher level of infection. Dietary protein deficiency increased parasite survival at high infection levels. Heavily infected hosts fed the 16% protein diet were found to expel almost the whole of their infections around day 21 p.i. By contrast, this response appeared defective in hosts fed the lower 4% protein diet, resulting in the establishment and survival of large, chronic and patent infections. Mean faecal egg output per mouse increased with infection dose in animals fed a low protein diet, but was low and unrelated to infection exposure in hosts fed the 16% protein diet. It is concluded that low protein levels in diet, via alterations in host resistance, may have an important influence on the transmission of T. muris.

The influence of host dietary protein on acquired immunity and intestinal helminth population dynamics during repeated infection was studied using the mouse–Trichuris muris experimental model. CBA/Ca mice fed a 2% (by mass) protein diet ad libitum maintained body weight during the experiment, but when fed diets containing either 4% or 16% (by mass) protein gained weight steadily. Infection with T. muris did not affect the growth of the latter mice but significantly reduced the growth of animals fed on the 2% protein diet. When repeatedly infected with either 5 or 50 eggs every 10 days, the mice fed the 2% or 4% protein diet accumulated adults in proportion to infection dose. The results show that this is due to both the establishment of larvae at each repeated infection and the survival of established adults. In contrast, very few worms were recovered from animals fed the 16% protein diet, principally as a result of the development of strong acquired immunity to reinfection. T. muris egg output/mouse increased with infection dose in animals fed the low protein diets, but no parasite eggs were detected in the faeces of hosts fed the 16% protein diet. Mouse antibody reponses to adult worm excretory/secretory antigen were time- and infection dose-dependent in all 3 dietary groups. The major finding was that the specific antibody response was more intense, both quantitatively (serum OD levels) and qualitatively (antigen recognition by IgG1), in mice fed the low protein diets, even though they remained susceptible to infection. This study shows that host dietary protein deficiency, even at levels irrelevant to normal growth, can markedly potentiate the transmission of T. muris via alterations in host resistance. The high levels of antibody in susceptible animals suggest that this defect in resistance is unlikely to be due to nutrient deficiency-associated defects in humoral immunity.

We investigate the computational structure of the biological kinship assignment problem by abstracting away all biological details that are irrelevant to computation. The computational structure depends on phenotype space, which we formally define. We illustrate this approach by exhibiting an approximation algorithm for kinship assignment in the case of the Simpson index with a priori error bound and running time that is polynomial in the bit size of the population, but exponential in phenotype space size. This algorithm is based on a relaxed version of the assignment problem, where fractional assignments (over the reals) are permitted.

In this study we examine the population biology of Brueelia apiastri, a chewing louse living on the European bee-eater (Merops apiaster). We investigate the relationships between parasite intensity of infestation, sex ratio, reproductive output, parasite size and their environment i.e. the morphology, condition, age and sex of the host. Chewing lice were collected, their sex and age (developmental stage) identified and parasite body size determined as a measure of parasite condition (larger individuals consume larger meals and larger females may produce larger clutches). The data show that there is variation in intensity as well as body size of B. apiastri between individual bee-eaters and this variation is independent of the sex of the birds. However, size, condition and age of the birds seem to influence the infestation rates with B. apiastri. The study suggested size-dependent depredation, since more, smaller chewing lice (usually nymphs) living on birds in better condition and birds having longer bills. Furthermore, more male chewing lice (males are smaller than females) live on older birds. Intraspecific competition between parasites seems to have a negative effect on female but not male body size but this result could be also explained by size-dependent depredation.

Specimens of Xanthoria parietina were collected from worldwide locations and ascospore discharge used to establish axenic cultures of the mycobiont. DNA was extracted and RAPD-PCR fingerprinting of 59 isolates was successfully achieved, resulting in 58 unique fingerprints. 110 multilocus RAPD markers were generated and used to construct a dendrogram. Two main groups were distinguished (75% bootstrap support): the first comprising samples from the Iberian Peninsula, the Balearic and Canary Islands; the second comprising all other worldwide samples including isolates from throughout Europe and North America. Samples from Australia and New Zealand clustered with the second group except one additional, phenotypically distinct specimen, not belonging to X. parietina, which formed an outgroup. However, comparative DNA sequence analyses are required to verify this interpretation.

Irrigation for intensive sugar cultivation started in the early 1980s at Richard Toll, some 100 km from the mouth of the Senegal River. Infections with Schistosoma mansoni were first seen in late 1988. This study records quantitative snail surveys for over 3 years from 1992 at sites representing different habitats in and around the irrigation scheme. Populations of both Biomphalaria pfeifferi (the intermediate host of S. mansoni) and Bulinus spp. (mainly B. truncatus, the local host of S. bovis) peaked in late ‘spring' or early ‘summer', depending on the habitat, and then remained low until the following ‘spring'. B. pfeifferi favoured smaller, man-made habitats with most transmission between May and August each year. The less abundant Bulinus spp. favoured larger natural and man-made habitats with most S. bovis transmission between April and July. S. mansoni infections were more, but S. bovis infections were less abundant than other trematodes in their respective snail hosts. Ecological changes in the early 1980s due to sugar irrigation pre-dated similar, more widespread changes in the late 1980s when the completion of dams across the Senegal River prevented seasonal rain fed floods and sea water intrusion. S. mansoni has since spread rapidly around Richard Toll. The incompatibility of the local S. haematobium strains with the dominant bulinid snails has so far prevented an epidemic of urinary schistosomiasis at Richard Toll, but the invasion of similar downstream habitats by susceptible B. globosus is worrying. The principal control measure, chemotherapy, given in the ‘winter' would minimise the rate of reinfection. It could be reinforced by judicious mollusciciding within the sugar irrigation scheme but not elsewhere.