Fine root distribution of trees and understory in mature stands of maritime pine (Pinus pinaster) on dry and humid sites

Maritime pine (Pinus pinaster) is the main tree cropping species in the Landes of Gascogne forest range in south western France. Soils are nutrient poor, sandy podzosols and site fertility is determined essentially by organic matter content and depth of water table, which is known to limit root growth. We hypothesised, with an ultimate goal of constructing a nutrient uptake model applicable to this region, that the organic top horizons together with the depth of the water table should be the most important parameters related to fine root distribution and presence of associated mycorrhiza. To test this hypothesis, we compared two adult Pinus pinaster stands, contrasting in depth of water table and soil fertility and evaluated fine roots (diameter ≤2 mm) of understory species and fine roots and ectomycorrhizal morphotypes of Pinus pinaster down to 1.2 m, using a soil corer approach. Total fine root biomass of Pinus pinaster was not significantly different between both sites (3.6 and 4.5 t ha⁻¹ for the humid, respectively, dry site), but root distribution was significantly shallower and root diameter increased more with depth at the humid site, presumably due to more adverse soil conditions as related to the presence of a hardpan, higher amount of aluminium oxides and / or anoxia. Fine roots of Pinus pinaster represented only about 30% of total fine root biomass and 15% of total fine root length, suggesting that the understory species cannot be ignored with regards to competition for mineral nutrients and water. A comparison of the ectomycorrhizal morphotypes showed that the humid site could be characterised by a very large proportion of contact exploration types, thought to be more relevant in accessing organic nutrient sources, whereas the dry site had a significantly higher proportion of both long-distance and short-distance exploration types, the latter of which was thought to be more resistant to short-term drought periods. These results partly confirm our hypothesis on root distribution as related to the presence of soil mineral nutrients (i.e. in organic matter), point out the potential role of understory plant species and ectomycorrhizal symbiosis and are a valuable step in building a site-specific nutrient uptake model.     

Demographic population structure of black howler monkeys in fragmented and continuous forest in Chiapas,Mexico: Implications for conservation

For wild primates, demography studies are increasingly recognized as necessary for assessing the viability of vulnerable populations experiencing rapid environmental change. In particular, anthropogenic changes such as habitat loss and fragmentation can cause ecological and behavioral changes in small, isolated populations, which may, over time, alter population density and demographic structure (age/sex classes and group composition) in fragment populations relative to continuous forest populations. We compared our study population of Endangered black howler monkeys (Alouatta pigra) in 34 forest fragments around Palenque National Park (PNP), Mexico (62 groups, 407 individuals), to the adjacent population in PNP, protected primary forest (21 groups, 134 individuals), and to previous research on black howlers in fragments in our study area (18 groups, 115 individuals). We used χ² and Mann–Whitney U tests to address the questions: (a) what is the current black howler demographic population structure in unprotected forest fragments around PNP? (b) How does it compare to PNP's stable, continuous population? (c) How has it changed over time? Compared to the PNP population, the fragment populations showed higher density, a significantly lower proportion of multimale groups, and significantly fewer adult males per group. The population's age/sex structure in the fragmented landscape has been stable over the last 17 years, but differed in a higher proportion of multifemale groups, higher density, and higher patch occupancy in the present. In the context of conservation, some of our results may be positive as they indicate possible population growth over time. However, long-term scarcity of adult males in fragments and associated effects on population demographic structure might be cause for concern, in that it may affect gene flow and genetic diversity. The scarcity of adult males might stem from males experiencing increased mortality while dispersing in the fragmented landscape, whereas females might be becoming more philopatric in fragments.     

Age,growth and reproduction of Marcusenius pongolensis,Oreochromis mossambicus and Schilbe intermedius in an oligotrophic impoundment in Swaziland

The age, growth and reproductive biology of Marcusenius pongolensis, Oreochromis mossambicus and Schilbe intermedius were investigated in the Mnjoli Dam, Swaziland. Otolith annulus formation occurred in winter for M. pongolensis, and in spring/summer for O. mossambicus and S. intermedius. Maximum ages of 8, 6 and 8 years were recorded for M. pongolensis, O. mossambicus and S. intermedius, respectively. Growth was described by the von Bertalanffy growth model as L_t = 238.73(1 − exp^{−0.27(t+2.27}) mm fork length (FL) for M. pongolensis, L_t = 226.83(1 − exp^{−0.45(t+2.02)}) mm total length (TL) for O. mossambicus, and L_t = 214.59(1 − exp^{−0.60(t+1.20)}) mm FL for S. intermedius. Sexual maturity was estimated for male and female M. pongolensis at 134 mm FL and 119 mm FL, respectively. Marcusenius pongolensis matured within their first year. Female O. mossambicus and S. intermedius matured at 239 mm TL and 205 mm FL, corresponding to 2 and 4 years of age, respectively. Extended spawning periods, with two spawning peaks was observed for M. pongolensis, one in spring (September) and the second in autumn (March) and one peak over late‐summer for S. intermedius.     

Colony structure, provisioning and sex allocation in the sweat bee Halictus ligatus (Hymenoptera: Halictidae)

Population and colony-level sex allocation and nest productivity in the eusocial sweat bee Halictus ligatus Say were studied by excavating nests during one season. The emphasis was on measuring the provision masses, which differ in size and shape depending on the sex of the egg to be laid on them (male-producing provision masses are smaller and more or less round, whereas gyne-producing provision masses are larger and 'loaf-shaped). The primary aim of this study was to test theoretical predictions about female-bias of the sex ratio in the summer brood, both on the population level and on the colony level.
The overall sex ratio of the summer brood was moderately biased towards gynes. A significant positive correlation between the overall size of provision masses (as an estimate for the degree of female bias of the nest sex ratio) and the number of eusocial workers was found. This relationship further improved in partial analyses in which the provision mass weights were adjusted for sampling date, removing the effect of protandry. Foundress size, however, had no effect on the second brood provision masses and neither was there an effect of worker number on the size of gynes and males separately. In the first brood only the size of the foundress had a consistently positive effect on the size of the provision masses and on the size of the emerging daughter workers.
The observed increase of female bias in the nest sex ratio with increasing numbers of eusocial worker bees conforms to optimization predictions following from kin-selection theory.     

Prey: predator ratio dependence in the functional response of a freshwater amphipod

1. First known for their shredding activity, freshwater amphipods also behave as active predators with consequences for prey population regulation and amphipod coexistence in the context of biological invasions. 2. A way to quantify predation is to determine the average consumption rate per predator, also known as its functional response (FR). 3. Although amphipods are gregarious and can display social interactions that can alter per capita consumption rates, previous studies using the FR approach to investigate amphipod predation ignored such potential mutual interference because they did not consider variations in predator density. 4. We investigated the FR of Echinogammarus berilloni feeding on dipteran larvae with joint variations in prey and predator densities. This bivariate experimental design allowed us to estimate interference and to compare the fits of the three main classes of theoretical FR models, in which the predation rate is a function of prey density alone (prey‐dependent models), of both prey and predator densities (predator‐dependent models) or of the prey‐to‐predator ratio (ratio‐dependent models). 5. The Arditi–Ginzburg ratio‐dependent FR model provided the best representation of the FR of E. berilloni, whose predation rate showed a decelerating rise to a horizontal asymptote as prey abundance increased. 6. Ratio dependence means that mutual interference between amphipods leads to prey sharing. Mutual interference is likely to vary between amphipod species, depending on their level of aggressiveness.     

The Effect of Traffic Density on Lead Contents in Roadside Soils: An Analysis of Published Data

Data from eight published studies were combined to show that the influence of traffic density on Pb contents in roadside soils increases with proximity to the road.     

High herkogamy but low reciprocity characterizes isoplethic populations of Jasminum malabaricum,a species with stigma‐height dimorphism

• Studies of floral polymorphisms have focused on heterostyly, while stigma‐height dimorphism has received considerably less attention. Few studies have examined the reproductive biology of species with stigma‐height dimorphism to understand how factors influencing mate availability and pollen transfer are related to morph ratios in populations.
• Floral morphological traits, especially herkogamy and reciprocity, pollinator visitation, breeding system and spatiotemporal mate availability, are known to affect inter‐morph pollination and morph ratios in species with stigma‐height dimorphism. In this study, we investigated the presence of stigma‐height dimorphism and estimated morph ratios in four naturally occurring populations of Jasminum malabaricum. We quantified morph‐ and population‐specific differences in the abovementioned factors in these populations to understand the observed morph ratios.
• The positions of anthers and stigmas were characteristic of stigma‐height dimorphism, the first report of this polymorphism in the genus. All study populations were isoplethic, implying equal fitness of both morphs. Herkogamy was higher in the short‐styled morph, while reciprocity was higher between the long‐styled stigma and short‐styled anthers. Long‐ and short‐tongued pollinators were common floral visitors, and we observed no differences between morphs in spatiotemporal mate availability or pollinator visitation. Neither morph exhibited self‐ or heteromorphic incompatibility.
• The short‐styled stigma had lower reciprocity but likely receives sufficient inter‐morph pollen from long‐tongued pollinators, and also by avoiding self‐pollination due to higher herkogamy. These results highlight the importance of sufficient effective pollinators and floral morphological features, particularly herkogamy, in maintaining isoplethy in species with stigma‐height dimorphism.

     

Estimating Abundance From One-Dimensional Passive Acoustic Surveys

ABSTRACT Conventional distance sampling, the most-used method of estimating animal density and abundance, requires ranges to detected individuals, which are not easily measured for vocalizations. However, in some circumstances the sequential pattern of detection of vocalizations along a transect line gives information about the range of detection. Thus, from a one-dimensional acoustic point-transect survey (i.e., records of vocalizations detected or not detected at regularly spaced listening stations) it is possible to obtain a useful estimate of density or abundance. I developed equations for estimation of density for one-dimensional surveys. Using simulations I found that for the method to have little bias when both range of detection and rate of vocalization need to be estimated, stations needed to be spaced at 30–80% of the range of detection and the rate of vocalization should be >0.7. If either the range of detection or rate of vocalization is known, conditions are relaxed, and when both parameters are known the method works well almost universally. In favorable conditions for one-dimensional methods, estimated abundances have overall errors not much larger than those from conventional line-transect distance sampling. The methods appeared useful when applied to real acoustic data from whale surveys. The techniques may also be useful in surveys with nonacoustic detection of animals.     

Reproductive bionomics and life history traits of three gammaridean amphipods, Cymadusa filosa Savigny, Ampithoe laxipodus Appadoo and Myers and Mallacoota schellenbergi Ledoyer from the tropical Indian Ocean (Mauritius)

The reproductive bionomics and life history traits of two corophiid amphipods (Ampithoe laxipodus, Cymadusa filosa) and one melitid (Mallacoota schellenbergi) were studied in Mauritius (Indian Ocean) for the period March 1999 to February 2000. Results on the population structure, monthly size class variations, sex ratio, female reproductive states and fecundity are presented. The study demonstrates multivoltinism and continuous reproduction in the three species. Increase in number of juveniles was observed in warmer months for C. filosa and A. laxipodus. Sexual maturity was attained at smaller sizes in warmer months in the three species. Linear relationship on body length and number of eggs in brood pouch are presented. Size-independent analysis of egg number revealed a decrease in number of eggs in cooler months. Sex ratio is male skewed in M. schellenbergi and female skewed in C. filosa and A. laxipodus. Some of the plausible explanations for the reproductive strategies adopted by these three species in a tropical system are discussed.     

The effects of temperature and body size on the mating pattern of a gregariously nesting bee, Colletes cunicularius (Hymenoptera: Colletidae)

Abstract. 1. In a 3-year study of the solitary bee Colletes cunicularius L. in Sweden, average body size and population density fluctuated greatly between years.
2. In this protandrous population, females mated just once and the sex ratio was slightly male biased. Males were smaller than females.
3. Size assortative mating (homogamy), associated with an increase in population density during the central days of female emergence and mating, was observed in two out of three years. Homogamy was also observed in pairs with remating males.
4. Most of the mating males had emerged the day they mated, but 42% were older. We found no support for a general large-male mating advantage.
5. Weight of emerging females and mating males were negatively correlated with ground temperature, indicating thermoregulatory influence on the process of sexual selection in this species.