Estimating the stocking potential of fish in impoundments by modelling supply and steady‐state demand

1. Fish stocking is an increasingly common management tool for freshwater and marine environments and is often used to create and maintain fisheries in closed waters. The densities at which fish are stocked can have a large impact on a stocking programme’s success and sustainability. Stocking densities in impoundment sport‐fisheries, for example, are often based on social or practical factors, and ecologically based stocking models are needed to assist the selection of stocking densities that are appropriate for the environment. 2. In this study, stocking density is calculated with a numerical model that balances the supply of prey production with the energetic demand of stocked fish. The model aims to deliver outcomes over a range of potential management objectives, by providing specific consumption scenarios that represent the trade‐off between population abundance and individual body size in stocked fisheries. 3. The model uses a steady‐state population approach to calculate stocking density, which optimises population consumption by maintaining a consistent biomass distribution and encourages sustainable stocking by considering the energetic needs of all cohorts. Carrying capacity is represented by the steady‐state stocking density under a minimum consumption scenario (when fish meet only their minimum energetic needs). The comparison between a desired consumption rate and the existing level of production is used to assess the status or ‘health’ of the existing population and is used to determine whether stocking can occur and whether stocking densities can be sustainably increased. The probability of incorrectly assuming populations are achieving a given consumption level is also estimated, which is an ideal approach for interpreting multiple probability distributions. 4. A Monte‐Carlo analysis of uncertainty was used to provide a probability distribution of stocking density of Australian bass (Macquaria novemaculeata) in three Australian impoundments under various seasonal and consumption scenarios. The likely consumption rates of the existing populations were determined using historical stocking densities, which showed that the three populations were of reasonable health, although one impoundment may be overstocked. The steady‐state stocking densities depended on the desired consumption rate, and there was an eightfold difference in the stocking density aimed at providing large ‘trophy’ fish and the density required to reach carrying capacity. 5. Model outputs of existing abundance and biomass density agreed with empirical estimates of abundance and relative density in these impoundments, which provides support to the model’s accuracy. This supply–demand approach to estimating the range of appropriate stocking densities shows promise as a decision‐support tool for stocked impoundments and other closed fisheries.     

Variable extent of sex‐biased dispersal in a strongly polygynous mammal

For mammals with a polygynous mating system, dispersal is expected to be male‐biased. However, with the increase in empirical studies, discrepancies are arising between the expected and observed direction/extent of the bias in dispersal. In this study, we assessed sex‐biased dispersal in red deer (Cervus elaphus) on 13 estates from the Scottish Highlands. A total of 568 adult individuals were genotyped at 21 microsatellite markers and sequenced for 821 bp of the mitochondrial control region. Estimates of population structure with mitochondrial sequences were eight times larger than that obtained with microsatellite data (F_{st′‐mt DNA} = 0.831; F_{st′‐micros} = 0.096) indicating overall male‐biased dispersal in the study area. Comparisons of microsatellite data between the sexes indicated a predominance of male‐biased dispersal in the study area but values of F_ST and relatedness were only slighter larger for females. Individual‐based spatial autocorrelation analysis generated a similar pattern of relatedness across geographical distances for both sexes, with differences only significant at two distance intervals (25–30 and 70–112 km). Patterns of relatedness differed between estates, male biased‐dispersal was detected in eight estates but no sex‐biased dispersal was found in the remaining five. Neither population density nor landscape cover was found to be associated with the patterns of relatedness found across the estates. Differences in management strategies that could influence age structure, sex ratio and dispersal behaviour are proposed as potential factors influencing the relatedness patterns observed. This study provides new insights on dispersal of a strongly polygynous mammal at geographical scales relevant for management and conservation.     

Use of trade-off theory to advance understanding of herbivore–parasite interactions

• 1 Trade‐off theory has been extensively used to further our understanding of animal behaviour. In mammalian herbivores, it has been used to advance our understanding of their reproductive, parental care and foraging strategies. Here, we detail how trade‐off theory can be applied to herbivore–parasite interactions, especially in foraging environments.
• 2 Foraging is a common mode of uptake of parasites that represent the most pervasive challenge to mammalian fitness and survival. Hosts are hypothesized to alter their foraging behaviour in the presence of parasites in three ways: (i) hosts avoid foraging in areas that are contaminated with parasites; (ii) hosts select diets that increase their resistance and resilience to parasites; and (iii) hosts select for foods with direct anti‐parasitic properties (self‐medication). We concentrate on the mammalian herbivore literature to detail the recent advances made using trade‐off frameworks to understand the mechanisms behind host–parasite interactions in relation to these three hypotheses.
• 3 In natural systems, animals often face complex foraging decisions including nutrient intake vs. predation risk, nutrient intake vs. sheltering and nutrient intake vs. parasite risk trade‐offs. A trade‐off framework is detailed that can be used to interpret mammal behaviour in complex environments, and may be used to advance the self‐medication hypothesis.
• 4 The use of trade‐off theory has advanced our understanding of the contact process between grazing mammalian hosts and their parasites transmitted via the faecal–oral route. Experimental manipulation of the costs and benefits of a nutrient intake vs. parasite risk trade‐off has shown that environmental conditions (forage quality and quantity) and the physiological state (parasitic and immune status) of a mammalian host can both affect the behavioural decisions of foraging animals.
• 5 Naturally occurring trade‐offs and the potential to manipulate their costs and benefits enables us to identify the abilities and behavioural rules used by mammals when making decisions in complex environments and thus predict animal behaviour.

     

Anti-bat tiger moth sounds: Form and function

The night sky is the venue of an ancient acoustic battle between echolocating bats and their insect prey. Many tiger moths (Lepidoptera: Arctiidae) answer the attack calls of bats with a barrage of high frequency clicks. Some moth species use these clicks for acoustic aposematism and mimicry, and others for sonar jamming, however, most of the work on these defensive functions has been done on individual moth species. We here analyze the diversity of structure in tiger moth sounds from 26 spe-cies collected at three locations in North and South America. A principal components analysis of the anti-bat tiger moth sounds reveals that they vary markedly along three axes: (1) frequency, (2) duty cycle (sound production per unit time) and frequency modulation, and (3) modulation cycle (clicks produced during flexion and relaxation of the sound producing tymbal) structure. Tiger moth species appear to cluster into two distinct groups: one with low duty cycle and few clicks per modulation cycle that supports an acoustic aposematism function, and a second with high duty cycle and many clicks per modulation cycle that is con-sistent with a sonar jamming function. This is the first evidence from a community-level analysis to support multiple functions for tiger moth sounds. We also provide evidence supporting an evolutionary history for the development of these strategies. Further-more, cross-correlation and spectrogram correlation measurements failed to support a "phantom echo" mechanism underlying sonar jamming, and instead point towards echo interference.     

ENHANCING EVOLUTION AND ENHANCING EVOLUTION

It has been claimed in several places that the new genetic technologies allow humanity to achieve in a generation or two what might take natural selection hundreds of millennia in respect of the elimination of certain diseases and an increase in traits such as intelligence. More radically, it has been suggested that those same technologies could be used to instil characteristics that we might reasonably expect never to appear due to natural selection alone. John Harris, a proponent of this genomic optimism, claims in his book Enhancing Evolution that we not only have it in our power to enhance evolution, but that we also have a duty to do so. In this paper, I claim that Harris' hand is strong but that he overplays it nevertheless. He is correct to dismiss the arguments of the anti‐enhancement lobby and correct to say that enhancement is permissible; but ‘good’ is different from ‘permissible’ and his argument for the goodness of enhancement is less convincing. Moreover, he is simply wrong to claim that it generates a duty to enhance.     

Neutral Lipids Rigidify Unsaturated Acyl Chains in Senescing Membranes

Senescence in bean cotyledons is accompanied by a progressiveincrease in the proportion of gel phase lipid in cellular membranesthat can be attributed to qualitative changes in the neutrallipids. The resulting mixture of lipid phases leads to impairedmembrane function. Insight into the molecular basis for thisphenomenon has been gleaned from studies of the effects of theseneutral lipids on the phase properties of pure phospholipidmembranes. Induction of the gel phase, detectable as a risein the liquid-crystalline to gel phase transition temperature,was observed when neutral lipid from senescent membranes wasintroduced into liposomes of unsaturated phospholipids. Thetransition temperature for phosphatidylcholine rose from –6.5° C in control liposomes to 51 ° C when 25% (w/w) neutrallipid was present. A similar rise was obtained for dioleoylphosphatidylcholine.However, for dipalmitoylphosphatidylcholine, which is fullysaturated, the rise in transition temperature upon additionof neutral lipids was only 3 ° C. Thus the neutral lipidsin senescent membranes appear to selectively rigidify unsaturatedacyl chains. At least three types of compounds known to alterthe phase properties of lipid bilayers were detectable in theneutral lipid fraction, suggesting that rigidification reflectsthe concerted action of several neutral lipid components onunsaturated phospholipid. Key words: Senescence, phospholipid, lipid phase properties     

Leaf chemistry of woody plants in relation to season,canopy retention and goat browsing in a semiarid subtropical savanna

Abstract It is assumed that the phytochemistry of browse species protects their biomass and nutrients against herbivory. In this study we were primarily interested in (i) seasonal and phenology‐related variations in leaf chemistry, and (ii) chemistry‐related variations in the feeding behaviour of domestic goats. Such knowledge would guide management‐orientated modelling of browse–browser interactions in seasonal, subtropical zones where goats are abundant. The browse species studied were typical of semiarid savannas in southern Africa: Grewia occidentalis L. (Tiliaceae), Scutia myrtina (Burm. f) Kurz (Rhamnaceae), Diospyros lycioides Desf. ssp. lycioides (Ebenaceae), Rhus longispina Eckl. and Zeyh. (Anacardiaceae), Ehretia rigida (Thunb.) Druce (Boraginaceae) and Acacia karroo Hayne (Mimosoideae). Nitrogen (N), phosphorus (P), condensed tannins (CT), protein‐precipitating tannins (PPT), total phenols (TP), cellulose and lignin concentrations were estimated for each species during the late dormant and early growing seasons. N, P, CT and TP were elevated during the growth season, while cellulose, lignin and PPT decreased. Unlike cytoplasm contents, which varied seasonally, cell wall and vacuole contents varied both seasonally and among species. Except that seasonal variation in N of deciduous species was greater than that of evergreen species, leaf phenology was not related to variations in forage quality. Short‐term intake rates were not related to primary metabolite concentrations, but were positively related to secondary metabolites. Elevated intake rates of putative defences were concluded to be side‐effects of attempts by goats to increase nutrient intake rate, indicating tolerance of chemical defences. Without support for the hypothesis that chemical defences are correlated to canopy retention, we propose an alternative hypothesis, that defences are distributed among woody plants in semiarid, subtropical savannas according to shoot morphology because it affects the vulnerability of plant parts to browsers.