A theory of stochastic harvesting in stochastic environments

We investigate how model populations respond to stochastic harvesting in a stochastic environment. In particular, we show that the effects of variable harvesting on the variance in population density and yield depend critically on the autocorrelation of environmental noise and on whether the endogenous dynamics of the population display over- or undercompensation to density. These factors interact in complicated ways; harvesting shifts the slope of the renewal function, and the net effect of this shift will depend on the sign and magnitude of the other influences. For example, when environmental noise exhibits a positive autocorrelation, the relative importance of a variable harvest to the variance in density increases with overcompensation but decreases with undercompensation. For a fixed harvesting level, an increasing level of autocorrelation in environmental noise will decrease the relative variation in population density when overcompensation would otherwise occur. These and other intricate interactions have important ramifications for the interpretation of time series data when no prior knowledge of demographic or environmental details exists. These effects are important whenever the harvesting rate is sufficiently high or variable, conditions likely to occur in many systems, whether the harvesting is caused by commercial exploitation or by any other strong agent of density-independent mortality.     

The relative importance of pre- and post-germination determinants for recruitment of an annual plant community on moving sandy land

• Background and Aims The relative importance of pre- and post-germination determinants for recruitment of natural plant communities is rarely explored. An annual plant community on moving sandy land was chosen for a case study. Answers to the following questions were sought: (a) Does recruitment of new individuals within the community of annual plants differ in time and space? (b) Is there spatial concordance between seed deposition, seedling emergence, survival and recruitment? (c) What are the direct and indirect effects of pre- and post-germination determinants on plant recruitment.• Methods An integrative approach combining investigation of natural recruitment processes with regression, correlation and path analyses was adopted. Data on seed deposition and seedling recruitment were collected by monitoring the number of seeds deposited in the top 5 cm of the soil and the numbers of seedlings emerged and recruited from all annual plants at sites to a range of distances from the existing shrub Artemisia halodendron (Asteraceae) in eight compass directions for two consecutive growing seasons.• Key Results Community-level recruitment was strongly affected by inter-annual rainfall variation and was highly site- and density-dependent. Low recruitment rate in this system was due to low emergence rate and low post-emergence survival rate. Of the pre- and post-germination determinants studied, it was the number of seedlings which emerged and the post-emergence survival rate that had the greatest direct effects on recruitment, with a combination of both variables explaining the majority of the variance (97 %) in recruitment.• Conclusions This study suggests that post-germination determinants (emergence and survival) rather than pre-germination determinants (seed deposition) substantially determined the final pattern of recruitment. Although the density of seeds deposited did not have a significant direct effect on recruitment, it contributed to observed variation in recruitment indirectly through density-dependent emergence of seedlings.     

Use of Green Manure Crops in Control of Hirschmanniella mucronata and H. oryzae in Irrigated Rice

Four field experiments were conducted to study the effect of Sesbania rostrata and Aeschynomene afraspera as rotational and green manure crops on the population dynamics of Hirschmanniella mucronata and H. oryzae, and subsequent rice yields. The sequential cropping of the legumes with rice controlled both nematode species. In two experiments, yield of rice was related to the nematode population denisites at planting and harvesting of the second rice crop (R² = 0.391, P < 0.001, and R² = 0.57, P < 0.001), regardless of the treatments. Rice yield increases were attributed to nutritional effect of the green manure and the reduction of the nematode populations or the modification of a factor(s) linked to the nematode populations induced by their cropping. As the two leguminous crops do not generate direct return, using them to control the rice-root nematodes was not economical, despite the significant yield increase obtained.     

Hunting Bambi—evaluating the basis for selective harvesting of juveniles

Human harvesting is often a major mortality factor and, hence, an important proximate factor driving the population dynamics of large mammals. Several selective harvesting regimes focus on removing animals with low reproductive value, such as “antlered” harvests in North America and juvenile harvesting in many European countries. Despite its widespread use and assumed impact, the scientific basis of juvenile harvesting is scattered in the literature and not empirically well-documented. We give the first overview of demographic, evolutionary and practical management arguments for selective harvesting of juveniles. Furthermore, we empirically test two demographic arguments based on harvest statistics of Red Deer (Cervus elaphus) in seven European countries. P₁: Harvesting juveniles has little influence on harvest growth compared with harvesting adult females due to the lower reproductive value of juveniles than adult females; P₂: Harvesting of juveniles dampens variance in harvest due to lower and more variable natural survival rates of juveniles compared with adults. We found that harvesting juveniles has little effect on harvest growth rate, while harvesting adult females has a significant negative effect (consistent with P₁), but that increasing the proportion of juveniles in the harvest did not decrease the variability in harvest between years (P₂ not supported). Based on our empirical findings and overview of arguments, we discuss how the merits of juvenile harvesting may vary over time as populations move from a low density to a very high density state.     

Effects of hybrid and maturity on performance and nutritive characteristics of forage maize at high latitudes, estimated using the gas production technique

We evaluated effects of hybrid and advancing plant maturity on performance, chemical composition, and nutritional characteristics of whole plant forage maize as well as the relative contributions of its plant fractions at high latitudes. Three maize hybrids, Avenir (FAO 180), Isberi (FAO 190) and Burli (FAO 210), were grown in southern Sweden in a field experiment with a replicated complete randomized block design. Plants were harvested four times during maturation, and dry matter (DM) yield and DM as a proportion of fresh weight were recorded. Whole plants were separated into four morphological fractions representing stems, leaves, kernels and cobs and the contribution of each fraction to the DM of the whole plant was estimated. Plant material was subjected to chemical analysis followed by measurement of in vitro gas production (GP) in buffered rumen fluid and finally, by calculation of in vitro true digestibility of organic matter (OM) and neutral detergent fibre (aNDFom). The GP profiles were fitted to a first order kinetic model with a discrete lag. Parameters describing the GP profiles were used in a recently developed mechanistic two compartment rumen degradation model to estimate in vivo OM digestibility (OMD) and first order rate of degradation in the rumen. Hybrids were compared and effects of maturity were assessed by analysis of variance using DM concentration as covariate. There were differences (P<0.05) among the hybrids in DM yield and relative contributions of the plant fractions. Differences (P<0.05) in modelled in vivo digestibility of OM and rates of degradation also occurred among hybrids. Increased maturity caused a reduction in in vitro digestibility of aNDFom in all plant fractions (P<0.05), but increased the rate of rumen degradation of OM in the whole plant as evaluated from GP results. The DM yield had a quadratic relationship with increasing maturity, with maximum yield at a DM concentration of about 370 g/kg. In vitro GP can describe the nutritive characteristics of forage maize in relation to advancing maturity and increased maturity affected agronomic performance and plant composition as well as the nutritive characteristics of hybrids.     

Effects of experimental harvesting on recruitment of an alien mussel Mytilus galloprovincialis

Successful fisheries management is underpinned by an understanding of the processes that underlie the population dynamics of exploited stocks. This study considered the effects of experimental harvesting on recruitment of Mytilus galloprovincialis along the west coast of South Africa, where harvesting of this alien species is being contemplated. In particular, the role of settlement habitat availability in the form of adult mussels was analysed. To track the effects of a spectrum of harvesting intensities, five treatments were implemented: F = 0 (i.e. a control), F = 0.3, F = 0.6, F = 0.9 and F = 1. At these harvesting intensities 0%, 30%, 60%, 90% or 100% of mussel biomass was removed respectively at the outset of the experiment. A significant negative exponential relationship (p < 0.01) was found between M. galloprovincialis recruit density and harvesting intensity, with intensities greater than F = 0.3 dramatically reducing recruitment. This pattern was recorded throughout the intertidal zone and remained temporally constant over 2 years. Significant positive linear relationships (p < 0.01) between recruit density and adult mussel biomass or density indicate a strong correlation between availability of settlement habitat and recruitment. It is likely that the high recruit density recorded at low harvesting intensities (2000-20 000 per 0.01 m²) exceeds the level required for population maintenance. However, if settlement habitat is eliminated or significantly reduced, as was achieved by F = 0.3 or above, recruitment may become limiting. Thus, to protect stock replenishment, harvesting of M. galloprovincialis in this region should take place at intensities less than F = 0.3.     

Intraspecific variation influences natural settlement of eastern oysters

As populations decline, their intraspecific diversity also diminishes. Population decline may be exacerbated if a decrease in intraspecific diversity also reduces important ecological functions that maintain population numbers. Oyster reefs are severely overharvested, declining by ~85 % worldwide. We tested how increasing within-species diversity of eastern oysters (Crassostrea virginica) using transplants would affect recruitment of oyster larvae, a key function necessary to maintain future populations. If harvesting reduces population numbers, within-species diversity, and connectivity, then oysters may lose the ability to adapt to changing environmental conditions as well as incur lower levels of recruitment that may hasten their decline. Results from laboratory and field studies indicated that oyster larvae use chemical cues from adult oysters and not from associated fouling communities to select settlement sites. To test how increasing within-species diversity of oysters affected recruitment, we collected oysters from three distinct bay systems in Texas, USA, and compared natural settlement in treatments where all oysters were from a single bay to a mixture of all three bays. Significantly greater recruitment occurred in mixed treatments in 2010, 2011, and 2012 even though oyster recruitment varied by order of magnitude during this time. The net biodiversity effect was positive in all 3 years, indicating that increased recruitment in mixed treatments can be greater than the additive effect of the single bay treatments. Losing intraspecific diversity may reduce recruitment and lead to further declines in oyster populations, illustrating the need for understanding how intraspecific diversity influences ecological functions.     

Modelling harvesting strategies for the lobster fishery in northern Europe: the importance of protecting egg-bearing females

European lobster populations in Norway and Sweden are severely reduced as a result of intense harvesting over a long time. Various alternative management options have been proposed or endorsed to both facilitate recovery and increase yield. Accordingly, Minimum Landing Size (MLS) regulations are widely used for the European lobster. We developed an individual-based population model which integrates biological knowledge about lobsters’ population dynamics to explore how available harvesting strategies and management options influence abundance and yield. The model reproduced basic features of a real lobster population in Sweden. Even for a relatively large MLS high fishing effort may still be detrimental to the long term production of the stock, while increasing the MLS further prevents this recruitment overfishing. A moratorium on berried females, in combination with the MLS appears to stabilize population fluctuations and yield, leading to higher yield for all MLS's considered. The female moratorium harvesting strategy also performed better than a maximum size limit. Yield per recruit calculations gave similar quantitative results, and also shows that a larger MLS reduce the risk of growth overfishing. A smaller MLS enables the harvest of many individuals but is very sensitive to increase in effort which easily promotes overfishing.     

Facilitation and interference at the intraspecific level: Recruitment of Kageneckia angustifolia D. Don (Rosaceae) in the montane sclerophyllous woodland of central Chile

Most of the studies that have evaluated the interplay between interference and facilitation have been done at the interspecific level, whereas studies at the intraspecific level are scarce. The montane sclerophyllous forests of central Chile are dominated by the tree Kageneckia angustifolia, a semi-deciduous species that lose part of its foliage during summer. It has been reported that during winter snow accumulates in lower amounts beneath the canopy of K. angustifolia favoring the recruitment of new individuals compared to open areas (i.e., facilitation effect). However, it has also been reported that the leaf litter accumulated beneath parental trees contains allelopathic compounds that decrease seed germination, suggesting that recruitment beneath parental plants can be disfavored (i.e., interference effect). Hence, this system seems appropriate to assess the net-outcome between facilitative and negative effects during the emergence and survival of seedlings during the first year. In this study, we asked (i) what is the net-outcome between facilitative and interfering effects for K. angustifolia? (ii) does this net-outcome varies with the distance to parental trees? (iii) are positive and negative effects consistent through the seedling emergence and first year seedling survival phases? (iv) what are the main mechanisms behind the observed net-outcome? and (v) which is the optimal microhabitat for successful recruitment of this species? In an experimental plot of 10,000 m², we selected ten K. angustifolia trees and evaluated the effect of leaf litter on the emergence and survival of seedlings produced by experimentally sown seed seeds in three different microhabitats: beneath adult trees, edge of canopy and in open areas. In addition, we sampled three K. angustifolia stands to evaluate the microhabitat where the natural recruitment of this species actually occurring. Results showed that (1) seedling emergence was greater beneath canopy, intermediate in canopy edge and low in open areas, (2) whilst leaf litter significantly reduced seed germination, the magnitude of this negative effect was lower than the positive effect of beneath canopy microhabitat, (3) seedling survival was affected by microhabitats but not by the presence of leaf litter, (4) that the main mechanisms behind the observed patterns are the lower and delayed emergence of seedlings in open areas due to the longer duration of snow cover, decreasing the time to growth before the onset of summer drought, and (5) the greatest natural recruitment of K. angustifolia seedlings occurs beneath parental plants. Therefore, our findings suggest that the net-outcome between facilitative and interfering effect during the first year is mostly facilitative, indicating that adult trees of K. angustifolia are exerting a conspecific nurse effect on the recruitment of new individuals, a form of parental care in plants.     

Ontogeny of Foraging Competence in Capuchin Monkeys (Cebus capucinus) for Easy versus Difficult to Acquire Fruits: A Test of the Needing to Learn Hypothesis

Which factors select for long juvenile periods in some species is not well understood. One potential reason to delay the onset of reproduction is slow food acquisition rates, either due to competition (part of the ecological risk avoidance hypothesis), or due to a decreased foraging efficiency (a version of the needing to learn hypothesis). Capuchins provide a useful genus to test the needing to learn hypothesis because they are known for having long juvenile periods and a difficult-to-acquire diet. Generalized, linear, mixed models with data from 609 fruit forage focal follows on 49, habituated, wild Cebus capucinus were used to test two predictions from the needing-to-learn hypothesis as it applies to fruit foraging skills: 1) capuchin monkeys do not achieve adult foraging return rates for difficult-to-acquire fruits before late in the juvenile period; and 2) variance in return rates for these fruits is at least partially associated with differences in foraging skill. In support of the first prediction, adults, compared with all younger age classes, had significantly higher foraging return rates when foraging for fruits that were ranked as difficult-to-acquire (return rates relative to adults: 0.30–0.41, p-value range 0.008–0.016), indicating that the individuals in the group who have the most foraging experience also achieve the highest return rates. In contrast, and in support of the second prediction, there were no significant differences between age classes for fruits that were ranked as easy to acquire (return rates relative to adults: 0.97–1.42, p-value range 0.086–0.896), indicating that strength and/or skill are likely to affect return rates. In addition, fruits that were difficult to acquire were foraged at nearly identical rates by adult males and significantly smaller (and presumably weaker) adult females (males relative to females: 1.01, p = 0.978), while subadult females had much lower foraging efficiency than the similarly-sized but more experienced adult females (subadults relative to adults: 0.34, p = 0.052), indicating that skill, specifically, is likely to have an effect on return rates. These results are consistent with the needing to learn hypothesis and indicate that long juvenile periods in capuchins may be the result of selection for more time to learn foraging skills for difficult-to-acquire fruits.     

Biogenesis and light regulation of the major light harvesting chlorophyll-protein of diatoms

The apoprotein of the major light harvesting pigment-protein complex from the diatom Phaeodactylum tricornutum (UTEX 646) is composed of two similar polypeptides of 17.5 and 18.0 kilodaltons (kD). The in vivo synthesis of these polypeptides is inhibited by the 80s protein synthesis inhibitor cycloheximide, but not by the 70s ribosome inhibitor chloramphenicol. When total poly(A)⁺ RNA was used in in vitro protein synthesis, a number of polypeptides were synthesized with a dominant product at 22 kD. When the polypeptides were immunoprecipitated with monospecific antibodies to the 17.5 and 18.0 polypeptides, a single protein zone of 22 kD was detected. Immunoprecipitation with preimmune serum failed to precipitate detectable levels of protein at any relative molecular weight (M_r). These findings indicate that the two apoprotein polypeptides of the diatom light harvesting pigment-protein are translated from polyadenylated message on cytoplasmic ribosomes as either a single or two (or more) similar M_r precursor proteins. These findings also suggest that this protein is encoded in the nucleus.

Photosynthetic light adaptation features of P. tricornutum UTEX 646 indicate that it responds to low light by increasing cell size and numbers of photosystem I and II reaction centers per cell, but does not change photosynthetic rate per cell or photosynthetic unit sizes significantly. When low light cells are exposed to higher photon flux densities, the in vivo incorporation of label into the apoprotein of the light harvesting complex decreases. In contrast, high light grown cells show rapid (<3 hour) increases in apoprotein synthesis when exposed to low light levels. This is the first demonstration of a specific role of photon flux density in regulating the synthesis of a major light harvesting pigment-protein during photosynthetic light adaptation.

     

Anthropogenic Landscape in Southeastern Amazonia: Contemporary Impacts of Low-Intensity Harvesting and Dispersal of Brazil Nuts by the Kayapó Indigenous People

Brazil nut, the Bertholletia excelsa seed, is one of the most important non-timber forest products in the Amazon Forest and the livelihoods of thousands of traditional Amazonian families depend on its commercialization. B. excelsa has been frequently cited as an indicator of anthropogenic forests and there is strong evidence that past human management has significantly contributed to its present distribution across the Amazon, suggesting that low levels of harvesting may play a positive role in B. excelsa recruitment. Here, we evaluate the effects of Brazil nut harvesting by the Kayapó Indigenous people of southeastern Amazonia on seedling recruitment in 20 B. excelsa groves subjected to different harvesting intensities, and investigated if management by harvesters influences patterns of B. excelsa distribution. The number of years of low-intensity Brazil nut harvesting by the Kayapó over the past two decades was positively related to B. excelsa seedling density in groves. One of the mechanisms behind the higher seedling density in harvested sites seems to be seed dispersal by harvesters along trails. The Kayapó also intentionally plant B. excelsa seeds and seedlings across their territories. Our results show not only that low-intensity Brazil nut harvesting by the Kayapó people does not reduce recruitment of seedlings, but that harvesting and/or associated activities conducted by traditional harvesters may benefit B. excelsa beyond grove borders. Our study supports the hypothesis that B. excelsa dispersal throughout the Amazon was, at least in part, influenced by indigenous groups, and strongly suggests that current human management contributes to the maintenance and formation of B. excelsa groves. We suggest that changes in Brazil nut management practices by traditional people to prevent harvesting impacts may be unnecessary and even counterproductive in many areas, and should be carefully evaluated before implementation.     

Intertidal zonation of prosobranch gastropods: Analysis of densities of four co-existing species

The densities of populations of Nerita atramentosa Reeve, Austrocochlea constricta Lamarck, Bembiciuin nanum (Lamarck), and Cellana tramoserica (Sowerby) were recorded in 0.25 m² quadrats on landward and seaward halves of a sheltered and a moderately exposed rock platform from June 1972 to June 1973. The data have been subjected to variance and multiple regression analysis. Differences between densities of each species on the two shores and in the two areas of each shore are discussed with respect to the regressions on littoral height. Densities of Nerita on the sheltered shore, Austrocochlea and Bembicium on both shores, and Cellana, on the exposed shore, increased with height. The density of Cellana on the sheltered shore decreased as height increased. The density differences in the landward and seaward areas on the two shores were attributable to the effect of height for Nerita and Austrocochlea. Height was the major variable affecting the density of these two species on the sheltered shore. Bembicium and Cellana densities on both shores, and Austrocochlea density on the exposed shore, are not primarily determined by height.On the sheltered shore, Nerita and Cellana increased in density with increasing cover of water in rock pools. On the exposed shore, Bembicium and Cellana became sparser with increasing water cover. Bembicium on both shores increased in density with increasing cover of the alga Peyssonelia, as did Cellana on the exposed shore. Cellana and Austrocochlea tended to increase in density with Nerita on the sheltered shore. Cellana tended to be sparse where Bembicium was dense on the exposed shore. The biological effects of substrata and other species on the densities of each species remain unexplained.Significant time effects were found for variations in the densities of Nerita and Cellana on the sheltered shore and of Austrocochlea and Cellana on the exposed shore. The seasonal change in density of Nerita was parabolic with a minimum in summer, and is consistent with the known period of recruitment of this species. The lack of significant time effects on density of Austrocochlea on the sheltered shore is consistent with the known continuous recruitment of this species. The declining density of Austrocochlea on the moderately exposed shore was found, by size-frequency analysis, to be due to reduced recruitment compared with surrounding shores. The density of Cellana on both shores showed seasonal changes, with a maximum in summer, which is consistent with the known period of recruitment in Cellana. The lack of seasonal changes in density of Bembicium is briefly discussed.This type of multifactor analysis identifies biological interactions affecting variation in density of these species. It also corroborates the results of other ecological investigations and determines the relative importance of a variety of physical and biological factors in the distribution of density of intertidal gastropods.     

A New Method to Compare Statistical Tree Growth Curves: The PL-GMANOVA Model and Its Application with Dendrochronological Data

Growth curves are monotonically increasing functions that measure repeatedly the same subjects over time. The classical growth curve model in the statistical literature is the Generalized Multivariate Analysis of Variance (GMANOVA) model. In order to model the tree trunk radius (r) over time (t) of trees on different sites, GMANOVA is combined here with the adapted PL regression model Q = A·T+E, where for and for , A =  initial relative growth to be estimated, , and E is an error term for each tree and time point. Furthermore, Ei[–b·r]  = , , with TPR being the turning point radius in a sigmoid curve, and at is an estimated calibrating time-radius point. Advantages of the approach are that growth rates can be compared among growth curves with different turning point radiuses and different starting points, hidden outliers are easily detectable, the method is statistically robust, and heteroscedasticity of the residuals among time points is allowed. The model was implemented with dendrochronological data of 235 Pinus montezumae trees on ten Mexican volcano sites to calculate comparison intervals for the estimated initial relative growth . One site (at the Popocatépetl volcano) stood out, with being 3.9 times the value of the site with the slowest-growing trees. Calculating variance components for the initial relative growth, 34% of the growth variation was found among sites, 31% among trees, and 35% over time. Without the Popocatépetl site, the numbers changed to 7%, 42%, and 51%. Further explanation of differences in growth would need to focus on factors that vary within sites and over time.     

The effect of stage of maturity on yield and quality of maize grain and stover

Stage of maturity at the time of harvest is considered as one of the factors influencing the nutritive value of crop residues. Thus this study was carried out to assess the effect of harvesting maize at different stages of grain maturity on yield and quality of maize grain and stover. The maize crop was harvested at grain moisture content of 28–30, 20–23 and 10–12%, which were designated as Stages I, II and III, respectively. Grain yield, standardised to 12.5% moisture content, showed an increasing trend, whereas cob, stover, total crop residue and total biomass dry matter (DM) yield showed a decreasing trend with increasing stage of maturity (p>0.05). The declining trend in stover yield with increased stage of maturity was due mainly to leaf loss. There was a significant decrease (p<0.05) in crop residue–grain ratio and leaf–stem ratio and a significant increase in the harvest index and hectolitre weight of the grain as the grain moisture content decreased from about 30 to 10%. Maize stover harvested at Stage I had significantly higher (p<0.05) ash content than those harvested at Stages II and III. The crude protein (CP) content was significantly lower, whereas the neutral detergent fibre and cellulose contents were higher (p<0.05) in Stage III than in Stages I and II. There was a decreasing trend in in sacco DM degradability with increasing stage of maturity. The washing loss, potential degradability and effective DM degradability at 0.03 h⁻¹ rumen outflow rate were higher (p<0.05) in Stage I than in Stages II and III. The volume of gas produced after 3, 6, 12, 24, 48 and 72 h of incubation was higher (p<0.05) in Stage I than in Stages II and III. The a value (the intercept of the gas production curve) and the gas production potential (a+b) were higher (p<0.05) in Stage I than in Stage III. Reduction in the nutritive value of stover with increasing stage of maturity was characterised by reduction in CP contents and increasing concentration of fibrous constituents. These were reflections of changes in the morphological composition of stover and losses of nutrients within the morphological fractions with increasing stage of maturity.     

Influence of seed size and seed nature on recruitment in the polymorphic harvester ant Messor barbarus

In the polymorphic harvester ant Messor barbarus, the colony modulates response during foraging according to seed characteristics. The easiness of picking up small seeds (oat fragments or canaryseeds) shortens the time lapse between food discovery and the return of scouts to the nest, favouring the onset of recruitment and higher mobilisation rates than bigger seeds (whole oat). However, size is not the only criterion, as canaryseeds are preferred among small ones. A modulation of the trail laid by the first scouts also plays a role in the shaping of harvesting patterns and in the enhancement of recruitment towards small and/or preferred seed. This flexibility extends to the relative participation of the three worker sizes classes, which differs according to seed. Media are the most numerous at the foraging arena and largely responsible for trail-laying. Minor participate in seed harvesting and trail-laying, mostly when they can be efficient in carrying seeds, such as oat fragments. Major scarcely participate in harvesting and trail-laying, but are involved in the exploitation of bigger and/or preferred seed species. When faced with different seed species, M. barbarus seems thus to collectively adopt a “foraging time minimisation” rather than an “energetic gain per item harvested maximisation” strategy. Dynamics of foraging and division of labour between foragers of different sizes are related to both the workers’ ability to carry seed items, and the transfer of information to nestmates by trail-laying, all parameters that vary according to seed characteristics.     

Life history of a neotropical marsupial: Evaluating potential contributions of survival and reproduction to population growth rate

The relative effect of survival and reproductive rates to population growth rate is expected to be similar across species with similar life-histories. We employed a matrix population model and sensitivity and elasticity analysis to assess the absolute and relative importance of age-specific survival and fertility to population growth rate of Didelphis aurita (Didelphimorphia, Didelphidae) in a rural area of Rio de Janeiro, southeastern Brazil. The results were compared to expectations for mammals that mature early and have short generation time, such as D. aurita. Prospective analysis showed that changes in pouch young and juveniles survival would have large effects on population growth rate, relative to other vital rates, being the most critical time periods in the life cycle of D. aurita, whereas the effect of fertilities were always low. These findings do not fit to the observed pattern in mammals that mature early, where reproductive parameters have the largest relative influence on population growth rate. Although reproductive rates were characterized by a relatively small influence on population growth rate, they are still relevant because of their high variability and response to potential environmental disturbances. The first application of matrix population models to a neotropical rainforest marsupial provides information on marsupial demography and life-history strategy, increasing comprehension of this unknown group.     

Investigating the Efficacy of Integrating Energy Crops into Non-Profitable Subfields in Iowa

Within-field spatial variability reduces growers’ return on investment and overall productivity while potentially increasing negative environmental impacts through increased soil erosion, nutrient runoff, and leaching. The hypothesis that integrating energy crops into non-profitable segments of agricultural fields could potentially increase grain yield and biomass feedstock production was tested in this study using a statewide analysis of predominantly corn- and soy-producing counties in Iowa. Basic and rigorous controls on permissible soil and soil-carbon losses were imposed on harvest of crop residues to enhance year-to-year sustainability of crop and residue production. Additional criteria limiting harvesting costs and focus on large-area subfields for biomass production were imposed to reduce the impacts of energy crop integration on grain production. Model simulations were conducted using 4 years (2013–2016) of soil, weather, crop yield, and management practice data on all counties in Iowa. Miscanthus (Miscanthus x giganteus), switchgrass (Panicum virgatum), and crop-residue-based bioenergy feedstock systems were evaluated as biomass. Average energy crop and plant residue harvesting efficiencies were estimated at 50 and 60%, respectively. Because of higher potential yields, average logistics costs for miscanthus-based biomass production were 15 and 23% lower than switchgrass-based and crop residue-based biomass productions, respectively, under basic sustainability controls, and 17 and 26% lower under rigorous sustainability controls. Subfield shape, size, area, and harvest equipment size were the dominant factors influencing harvesting cost and efficiency suggesting that in areas where subfields are predominantly profitable or harvesting efficiencies low, other options such as prairie strips, buffer zones around fields, and riparian areas should be investigated for more profitable biomass production and sustainable farming systems.     

Optimization of flocculation conditions for Botryococcus braunii using response surface methodology

Biodiesel from microalgae is recognized as a desirable, renewable biofuel to replace petroleum-derived transport fuels. However, the efficient harvesting of microalgae is a major hurdle for commercialization. Therefore, the development of a cost-effective harvesting method is essential to reduce production cost. A partial factorial design was used to screen the main factors involved, which were the concentration of FeCl₃, the bioflocculant, and the time of slow mixing. Response surface methodology (RSM) was used to further investigate the optimal conditions for these factors on flocculation of Botryococcus braunii. Analysis of variance and other relevant tests confirmed the validity of the suggested model. The optimal conditions inferred from the obtained equation were 0.79 mM FeCl₃, 0.58 % (v/v) bioflocculant, and 180 sec of slow mixing for 1.1 g DCW L^?1 of B. braunii. The flocculating activity under these conditions was 90.6 %. By using RSM, the optimal conditions for flocculation of B. braunii could be reached more quickly and efficiently.     

Culling Versus Density Effects in Management of a Deer Population

Abstract: Wildlife managers often manipulate hunting regulations to control deer populations. However, few empirical studies have examined the level of hunting effort (hunter-days) required to limit population growth and demographic effects through harvesting of females. Moreover, the relative importance of density effects on population growth has not been quantified. We reconstructed a sika deer [Cervus nippon] population over a period of 12 years (1990–2001) using age- and sex-specific harvest data. Using cohort analysis, we analyzed population dynamics, focusing on 1) the relationship between hunting effort and hunting-induced mortality rate, 2) relative contributions of hunting mortality and recruitment of yearlings to annual changes in population growth rate, and 3) annual variation in recruitment rate. Population size increased until 1998 and declined thereafter. The population growth rate changed more in response to annual changes in recruitment rate than hunting mortality rate. Temporal variation in recruitment rate was not controlled by birth rate alone; direct density dependence, intensities of hunting mortality for fawns, and for females (≥2 yr of age), which accounted for the fawn survival rate, were required as factors to explain temporal variation. Density effects on the recruitment rate were not strong enough to regulate the population within the study period; high hunting mortality, with intensive female harvesting, was necessary to prevent population growth. Hunting effort was a good predictor of the hunting mortality rate, and female harvest had a negative effect on the recruitment rate through fawn survival. We suggest that >3,500 hunter-days and prioritization of female harvesting are required to prevent increases in this deer population.