The consequences of polyandry for population viability,extinction risk and conservation

Polyandry, by elevating sexual conflict and selecting for reduced male care relative to monandry, may exacerbate the cost of sex and thereby seriously impact population fitness. On the other hand, polyandry has a number of possible population-level benefits over monandry, such as increased sexual selection leading to faster adaptation and a reduced mutation load. Here, we review existing information on how female fitness evolves under polyandry and how this influences population dynamics. In balance, it is far from clear whether polyandry has a net positive or negative effect on female fitness, but we also stress that its effects on individuals may not have visible demographic consequences. In populations that produce many more offspring than can possibly survive and breed, offspring gained or lost as a result of polyandry may not affect population size. Such ecological ‘masking’ of changes in population fitness could hide a response that only manifests under adverse environmental conditions (e.g. anthropogenic change). Surprisingly few studies have attempted to link mating system variation to population dynamics, and in general we urge researchers to consider the ecological consequences of evolutionary processes.     

Mate sampling and choosiness in the sand goby

To date, mate choice studies have mostly focused on establishing which mates are chosen or how the choices are performed. Here, we combined these two approaches by empirically testing how latency to mate is affected by various search costs, variation in mate quality and female quality in the sand goby (Pomatoschistus minutus). Our results show that females adjust their mating behaviour according to the costs and benefits of the choice situation. Specifically, they mated sooner when access to males was delayed and when the presence of other females presented a mate sampling cost. We also found a positive link between size variation among potential mating partners and spawning delay in some (but not all) experimental conditions. By contrast, we did not find the number of available males or the females'' own body size (‘quality’) to affect mating latency. Finally, female mating behaviour varied significantly between years. These findings are notable for demonstrating that (i) mate sampling time is particularly sensitive to costs and, to a lesser degree, to variation among mate candidates, (ii) females'' mating behaviour is sensitive to qualitative rather than to quantitative variation in their environment, and (iii) a snapshot view may describe mate sampling behaviour unreliably.     

Economic evaluation of water loss saving due to the biological control of water hyacinth at New Year’s Dam,Eastern Cape province,South Africa

Water hyacinth Eichhornia crassipes is considered the most damaging aquatic weed in the world. However, few studies have quantified the impact of this weed economically and ecologically, and even fewer studies have quantified the benefits of its control. This paper focuses on water loss saving as the benefit derived from biological control of this plant between 1990 and 2013 at New Year’s Dam, Alicedale, Eastern Cape, South Africa. Estimates of water loss due to evapotranspiration from water hyacinth vary significantly; therefore, the study used three different rates, high, medium and low. A conservative raw agriculture value of R 0.26 per m³ was used to calculate the benefits derived by the water saved. The present benefit and cost values were determined using 10% and 5% discount rates. The benefit/cost ratio at the low evapotranspiration rate was less than one, implying that biological control was not economically viable but, at the higher evapotranspiration rates, the return justified the costs of biological control. However, at the marginal value product of water, the inclusion of the costs of damage to infrastructure, or the adverse effects of water hyacinth on biodiversity, would justify the use of biological control, even at the low transpiration rate.     

Toxin depletion has no effect on antipredator responses in common toad (Bufo bufo) tadpoles

Antipredator responses often involve changes in several phenotypic traits and these changes interactively influence fitness. However, gaining insight into how the overall fitness effect of the overall response comes about is notoriously difficult. One promising avenue is to manipulate a single defensive trait and observe how that modifies fitness as well as the expression of other inducible responses. In chemically‐defended animals, toxins are likely to be costly to produce but it is still unknown how their depletion influences other characteristics. In the present study, we artificially depleted bufadienolide toxin stores in common toad (Bufo bufo) tadpoles, and assessed the effect of this with respect to the interaction with predator presence and limited food availability. We found that toxin depletion in tadpoles did not significantly affect any of the measured life‐history traits. Tadpoles in the predator treatment exhibited an elevated development rate, although this was only apparent when food availability was limited. Also, body mass at metamorphosis was lower in tadpoles exposed to chemical cues indicating a predation threat and when food availability was limited. These results provide evidence that, in larval common toads, the expression of inducible defences may incur fitness costs, whereas chemical defences are either expressed constitutively or, if inducible, elevated toxin production has negligible costs.     

Direct seeding and outplantings in drylands of Argentinean Patagonia: estimated costs,and prospects for large‐scale restoration and rehabilitation

In large areas of the world that are deeply scarred by desertification and hampered by low capacity for natural regeneration, the scaling up of ecological restoration and rehabilitation can be achieved only if it is low in cost with high return on investment, and shows promise of providing long‐lasting social‐economic as well as ecological benefits. In the Monte Austral region of Patagonia Argentina, concerted efforts are underway to facilitate scaling up of ecological restoration and rehabilitation practices. Here, we evaluate financial costs and preliminary results of direct seeding as compared to outplanting of nursery‐grown seedlings of three native species (Atriplex lampa, Senecio subulatus var. subulatus, and Hyalis argentea var. latisquama) considered to be high‐priority dryland framework species. Comparative success is expressed in terms of plant survival and in monetary terms. The three candidate species showed low survival rates, ranging from 4.3 to 22.3%, after the first summer following direct seeding. In contrast, survival rates for planted seedlings of the same three taxa varied between 84 and 91%, after the first summer following reintroduction. However, cost of direct seeding varied between 1,693 and 1,772 US$ less per hectare, that is, 64% less than the cost of outplanting nursery seedlings. Therefore, in the search for ways to scale up ecological restoration and rehabilitation in drylands, direct seeding should receive more attention. We discuss the social and ecological perspectives and the way forward for direct seeding techniques in Patagonia. We also consider how costs could be reduced and effectiveness improved in large‐scale efforts.     

Assessing,with limited resources,the ecological outcomes of wetland restoration: a South African case

Resources for evaluating the ecological outcomes of ecosystem restoration projects are often limited, especially within government‐funded programs. In order to rapidly assess the ecological outcomes of wetland restoration, an improved approach has been developed, which was applied in the assessment of the ecological outcomes at nine restoration sites of South Africa's Working for Wetlands program. The sites encompass a diversity of restoration problems and land use contexts. The approach begins by distinguishing hydrogeomorphic (HGM) units, for which ecological condition is assessed and reported for hydrology, geomorphology, and vegetation pre‐ and post‐restoration. These three components are closely linked but, as demonstrated at some of the sites, may respond differentially to restoration interventions. For most HGM units, overall ecological condition was improved by between 10 and 30%, with the greatest contribution of restoration generally being to the hydrology component. Having determined the integrity and costs of the interventions, cost‐effectiveness is then reported in South African Rands per hectare equivalent restored, which was found to vary by more than an order of magnitude across the HGM units assessed. Cost‐effectiveness must be interpreted in the light of the long‐term integrity of the interventions, the site's landscape context, and the contribution of restoration to ecosystem services provision. Some sites may be considerably less cost‐effective than others, but the cost may nonetheless be justified if the sites make key contributions to ecosystem services provision. The study was conducted in the context of a formative evaluation and the findings are envisaged to improve wetland restoration practice.     

Patterns of livestock depredation and cost‐effectiveness of fortified livestock enclosures in northern Tanzania

Human–carnivore conflicts and retaliatory killings contribute to carnivore populations' declines around the world. Strategies to mitigate conflicts have been developed, but their efficacy is rarely assessed in a randomized case–control design. Further, the economic costs prevent the adoption and wide use of conflict mitigation strategies by pastoralists in rural Africa. We examined carnivore (African lion [Panthera leo], leopard [Panthera pardus], spotted hyena [Crocuta crocuta], jackal [Canis mesomelas], and cheetah [Acinonyx jubatus]) raids on fortified (n = 45, total 631 monthly visits) and unfortified (traditional, n = 45, total 521 monthly visits) livestock enclosures (“bomas”) in northern Tanzania. The study aimed to (a) assess the extent of retaliatory killings of major carnivore species due to livestock depredation, (b) describe the spatiotemporal characteristics of carnivore raids on livestock enclosures, (c) analyze whether spatial covariates influenced livestock depredation risk in livestock enclosures, and (d) examine the cost‐effectiveness of livestock enclosure fortification. Results suggest that (a) majority of boma raids by carnivores were caused by spotted hyenas (nearly 90% of all raids), but retaliatory killings mainly targeted lions, (b) carnivore raid attempts were rare at individual households (0.081 raid attempts/month in fortified enclosures and 0.102 raid attempts/month in unfortified enclosures), and (c) spotted hyena raid attempts increased in the wet season compared with the dry season, and owners of fortified bomas reported less hyena raid attempts than owners of unfortified bomas. Landscape and habitat variables tested, did not strongly drive the spatial patterns of spotted hyena raids in livestock bomas. Carnivore raids varied randomly both spatially (village to village) and temporally (year to year). The cost‐benefit analysis suggest that investing in boma fortification yielded positive net present values after two to three years. Thus, enclosure fortification is a cost‐effective strategy to promote coexistence of carnivores and humans.