Should I stay or should I go? Testing optimality models of stopover decisions in migrating birds

Time-minimizing migrants should leave a stopover site if the instantaneous speed of migration drops to the average speed of migration in the environment. This argument has been used in two different ways: either there is local variation in the fuel deposition rate and a fixed expected speed or there is global variation in the fuel deposition rate, i.e. locally experienced variation represents global variation along the route. The first case leads to a far steeper relationship between departure load and fuel deposition rate than the second case. So far, data on departure loads have mainly been analysed within the concept of local variation of the fuel deposition rate and the result that the observed slopes are much lower than predicted has been explained by changes in the expected speed along the route or by individual differences in the expected speed. We show here that the observed relationships generally fall close to the predictions for global variation. We propose that migrants use a behavioural rule which projects the current experience into the future and therefore interprets local variation as global variation. Received: 3 April 1999 / Received in revised form: 22 April 1999 / Accepted: 26 April 1999     

Is aridity restricting deforestation and land uses in the South American Dry Chaco?

In this paper, we explored how aridity influences the regional deforestation and land-use patterns (i.e. crops/pastures) in South American Dry Chaco. To do this, we contrasted land use during last decade (2001–2012) with a spatially explicit aridity index, which we complemented with a crop water balance model. Land-use classifications were performed by considering the temporal variability of NDVI from MODIS satellites, showing that 40 and 60% of deforested land was assigned to crops and pastures, respectively. Results indicate that although the regional deforestation pattern was not associated with the aridity gradient, with drier areas similarly deforested as wetter areas, contrasting differences were observed in the use of this land, with crops mostly located (90%) in wetter areas and pastures evenly distributed across the whole aridity gradient. This research highlighted the strong effect of water limitations on the land-use option after deforestation and may help to set the basis for future land-use planning policies.     

Correlation between nectar supply and aggression in territorial honeyeaters: causation or coincidence?

Summary A fundamental prediction of food-based economic models of territoriality is that animals will not defend territories if food is so abundant that defense will not improve access to food. Several studies of nectar-feeding birds support this prediction, with territoriality being rare or absent in years when nectar was particularly abundant. However, these results could potentially be an artefact of changes in bird density with nectar availability, and in at least some cases the correlations between territory defense and nectar availability could be purely coincidental. This paper reports the first experimental test of whether cessation of territory defense in nectar-feeding birds results from a direct response to abundance of nectar. New holland honeyeaters Phylidonyris novaehollandiae and white-cheeked honeyeaters P. nigra show pronounced changes in their levels of territorial aggression over the 7–8 months that they breed. These changes are predictable from economic considerations in that the birds are least aggressive in the months when nectar is extremely abundant. I tested whether the birds were responding to changes in nectar availability by providing sugar-water feeders at neutral locations that were easily accessible to territory holders, but far enough away from territories that intrusion rates were unaffected. I tested for responses at two time scales feeders were put out for 48-h periods in 1987, and were left out continuously from January to October 1988. The only effect was that territory holders visited feeders instead of flowers when floral nectar was scarce. They continued to defend their territories aggressively at those times, showed seasonal changes in aggressiveness similar to birds on a site without feeders, and did not shift their territories toward feeders. I conclude that the observed changes in aggressiveness are not responses to changes in nectar availability, and suggest alternative explanations.     

Weapons or mating signals? Claw shape and mate choice in a fiddler crab

Males often possess traits, such as horns, claws, and tusks, which are used during male–male combat. Studies suggest that selection has fine tuned these weapons to improve their effectiveness and that the shape of these weapons provides cues for males to assess the strength of rivals. Similarly, females might also assess a male’s weaponry to determine his value as a mate. The largest weapon relative to body size is the major claw of male fiddler crabs (genus: Uca). Males use their claws both as a weapon and as a courtship signal, waving it to attract females. We used robotic crabs in two-choice experiments to test female mating preferences based on male claw shape in Uca mjoebergi. First, females did not prefer conspecific claws over any of three alternatively shaped stimuli matched for color and for the rate and pattern of waving. The alternative stimuli were two different heterospecific claws and a plain rectangular shape. Second, females significantly preferred the alternative stimuli when they were presented at a faster wave rate. We conclude that claw shape in U. mjoebergi has not evolved under sexual selection imposed by female mating preferences and is more likely to have evolved under selection for effectiveness during male–male competition.     

Land or lover? Territorial defence and mutual mate guarding in the crimson-breasted shrike

Crimson-breasted shrikes produce duets which are used in interactions with neighbours and intruders. We examined two major hypotheses explaining duetting, the territorial defence and mate guarding hypotheses, using playback experiments. The responses of 12 pairs towards solo male, solo female and stereo duet playback were analysed using principal component analysis and ANOVA. The measures of response intensity revealed in most cases highly coordinated responses of the pair partners. Although these joint responses could suggest cooperative territorial defence or mutual mate defence, responses to the treatments differed between males and females in terms of three variables. Females increased their answer rates significantly in response to unpaired female intruders, compared to unpaired male intruders. During duet playback, females directed their responses equally at both intruding pair members. In contrast, males were equally responsive towards unpaired male intruders and intruding pairs, but in the latter case directed their responses at the male pair member. In the presence of unpaired female intruders, males increased their solo song rates, but in the presence of intruding pairs, they increased overlapping rates and duetted with their mates. These divergent responses suggest that females use duets for mate guarding against unpaired females, whereas males use solo songs for mate guarding and both solos and duets in territorial defence.     

Aging and improving reproductive success in horses: declining residual reproductive value or just older and wiser?

In many mammalian species, female success in raising offspring improves as they age. The residual reproductive value hypothesis predicts that each individual offspring will be more valuable to the mother as she ages because there is less conflict between the current and potential future offspring. Therefore, as mothers age, their investment into individual offspring should increase. Empirical evidence for an influence of declining residual reproductive value on maternal investment is unconvincing. Older mothers may not invest more, but may be more successful due to greater experience, allowing them to target their investment more appropriately (targeted reproductive effort hypothesis). Most studies do not preclude either hypothesis. Mare age significantly influenced maternal investment in feral horses living on the North Island of New Zealand. Older mares, that were more successful at raising foals, were more protective for the first 20 days of life, but less diligent thereafter. Total maternal input by older mothers did not seem to be any greater, but was better targeted at the most critical period for foal survival and a similar pattern was observed in mares that had lost a foal in the previous year. In addition, older mothers were more likely to foal in consecutive years, supporting the hypothesis that they are investing less than younger mares in individual offspring. Therefore, older mothers seem to become more successful by targeting their investment better due to experience, not by investing more in their offspring. Received: 22 September 1999 / Received in revised form: 30 October 1999 / Accepted: 6 November 1999     

Climatic niche divergence or conservatism? Environmental niches and range limits in ecologically similar damselflies

The factors that determine species' range limits are of central interest to biologists. One particularly interesting group comprises odonates (dragonflies and damselflies), which show large differences in secondary sexual traits and respond quickly to climatic factors, but often have minor interspecific niche differences, challenging models of niche-based species coexistence. We quantified the environmental niches at two geographic scales to understand the ecological causes of northern range limits and the coexistence of two congeneric damselflies (Calopteryx splendens and C. virgo). Using environmental niche modeling, we quantified niche divergence first across the whole geographic range in Fennoscandia, and second only in the sympatric part of this range. We found evidence for interspecific divergence along the environmental axes of temperature and precipitation across the northern range in Fennoscandia, suggesting that adaptation to colder and wetter climate might have allowed C. virgo to expand farther north than C. splendens. However, in the sympatric zone in southern Fennoscandia we found only negligible and nonsignificant niche differences. Minor niche differences in sympatry lead to frequent encounters and intense interspecific sexual interactions at the local scale of populations. Nevertheless, niche differences across Fennoscandia suggest that species differences in physiological tolerances limit range expansions northward, and that current and future climate could have large effects on the distributional ranges of these and ecologically similar insects.     

Do you not like Pigou, or do you not understand him? Tax aversion and revenue recycling in the lab

Tax-aversion reduces the likelihood that price rationing can be a politically viable tool for environmental protection. We examine the case of the classic Pigouvian tax to control a negative externality, and consider how recycling the revenues, labeling of the tax and information about its purpose affects the support for taxation. We test the support for taxation within a single-price market experiment, in which purchases by some buyers impose external costs on others. Observing behavior consistent with tax-aversion, we also find that recycling the revenues to more narrowly targeted groups seems to increase support for taxation. In the absence of narrow revenue recycling, labeling a Pigouvian instrument as a ‘tax’ may significantly lower the likelihood of voter support.     

To preserve or to develop? East Bay dredging project,South Caicos,Turks and Caicos Islands

The Turks and Caicos Islands are currently in the midst of an economic revolution from a marine-based provisional economy to a tourism economy. East Bay, South Caicos, is currently under construction with plans for a 160-unit condominium complex. Included in the project plan is removal of seagrass beds in front of the development to make a sandy beach for tourists. The aims of this study were to (i) describe the bathymetry and benthic habitat coverage of East Bay before dredging takes place and (ii) perform an economic valuation on the turtle grass beds that will be dredged using ecosystem valuation and emergy analysis techniques. The bathymetry survey revealed shallow waters (<1.5 m) until the reef drop off (～650 m offshore). Benthic habitat exhibits zonation following the general progression: sand plain, algal plain, seagrass, coral rubble and seagrass, rock and turf algae, and reef flat. Ecosystem services valued the proposed dredging area at USD $28,807 per year, compared to emergy analysis, which valued the proposed dredging site at USD $32,060 per year. The baselines presented in the study may facilitate a quantitative assessment of dredging impacts on turtle grass once dredging is complete and an economical cost-benefit-analysis of the dredging project to see whether the economic gains outweigh the ecological costs of dredging in front of the East Bay development.     

Sedentary or mobile? Variability in space and depth use of an exploited coral reef fish

Movement of fishes defines the distribution and abundance of populations and occurs on a range of spatial and temporal scales. To successfully parameterise assessments and design management strategies for exploited fish populations, knowledge and consideration of their movement patterns are essential. Since the efficacy of management approaches vary depending on the sedentary or mobile nature of the target species, presence, space use and depth utilisation were examined to understand the movement patterns of redthroat emperor Lethrinus miniatus. Sixty individuals were monitored for up to 12 months in an acoustic array comprising three coral reefs, and variation in space use and movement patterns was observed among 26 individuals. Half of the individuals were recorded only in proximity of one receiver along the reef edge, while the other half were detected at multiple receivers and used horizontal areas of approximately 4 km². Periods of non-detection and lower detection frequency at night (χ ₁ ²  = 342.157, P < 0.001) indicated individuals may move away from the monitored reef edge to the adjacent sandy habitat, but most movements outside the array remain unknown. Long-distance movement was recorded for one individual, recaptured ~160 km from the release location. Generally, no trends in depth use were apparent, L. miniatus inhabited a variety of depths, which were not related to individual size or time of day, yet some effect of month was evident. Variation in movement among adult L. miniatus indicates that while some individuals undergo broader-scale movement, spatial closures that cover individual reefs (>4 km²) could provide protection from fishing for the proportion of the population that displayed high site fidelity and moderate-sized activity spaces (over a period of up to 12 months).     

Differences in abalone growth and morphology between locations with high and low food availability: morphologically fixed or plastic traits?

Many species of sedentary marine invertebrates exhibit large spatial variation in their morphology, which allow them to occupy a broad geographic distribution and range of environmental conditions. However, the detection of differences in morphology amongst variable environments cannot determine whether these differences represent a plastic response to the local environment, or whether morphology is genetically fixed. We used a reciprocal transplant experiment to test whether ‘stunted’ blacklip abalone (Haliotis rubra) are the result of a plastic response to the environment or fixed genetic trait. Furthermore, we related environmental factors, that affect food availability (density of abalone, water movement, algal cover and reef topography), to differences in growth and morphology. Morphological plasticity was confirmed as the mechanism causing morphological variation in H. rubra. Individuals transplanted to sites with ‘non-stunted’ H. rubra grew significantly faster when compared to stunted controls, whilst individuals transplanted to stunted sites grew significantly slower compared to non-stunted controls. The growth response was greater for individuals transplanted from ‘non-stunted’ to ‘stunted’ sites, suggesting that the environmental stressors in morphologically ‘stunted’ habitat are stronger compared to locations of faster growing morphology. We propose that these differences are related to resource availability whereby low algal cover and topographic simplicity results in stunted populations, whereas high algal abundance and topographic complexity results in non-stunted populations.     

Ecological literacy and socio-demographics: who are the most eco-literate in our community,and why?

Ecological literacy is founded upon knowledge and understanding about how the ecological systems of the Earth function and support life. A widespread concern that levels of ecological literacy within many contemporary human communities are inadequate to enable effective decision-making about sustainable ways of living led to a rigorous and carefully designed assessment of over 1000 South Australian adults from diverse sectors including industry, government, nongovernment, business and community organisations. This assessment tested for local and global knowledge, including an understanding of the interconnection of natural systems with human society. Quantitative analyses revealed significant relationships between scores and a range of socio-demographic characteristics. Scores varied significantly with gender, age, education, employment, place of growing up and time spent in South Australia (SA). Highest average scores were found in males, middle-age groups, the most highly educated, those with science-related educational backgrounds, those working in environment-related fields, those who grew up in small town environments rather than in large towns or cities and in those who had spent more than 10 years in SA. These findings contribute to a broader study of factors associated with ecologically literate individuals and groups within the western and industrialised adult community of SA. They form a valuable foundation on which to build efforts to further understand and develop ecological literacy within our citizenry and governing bodies.     

Female foraging and male vigilance in white-tailed ptarmigan (Lagopus leucurus): opportunism or behavioural coordination?

For several species of birds, high rates of male vigilance are correlated with high rates of female foraging. This relationship is thought to ultimately result in higher reproductive success for females paired with highly vigilant males. However, previous research has not examined the behavioural mechanism that produces the correlation between male vigilance and rates of female foraging. Foraging females may take advantage of vigilance that males are using for other purposes. Alternatively, the purpose of male vigilance may be to increase females' ability to forage. We examined these alternatives by testing whether vigilance preceded or followed bouts of female foraging more often than would occur by chance alone, using simultaneous behaviour observations of pre-incubation pairs of white-tailed ptarmigan (Lagopus leucurus). Our results indicate that each member of a pair may influence the behaviour of the other. Females were more likely to initiate foraging bouts after males became vigilant than if their mate remained non-vigilant. Moreover, non-vigilant males were more likely to become vigilant if their mate was foraging than if she was engaged in some other activity. Despite the possibility that a sexual conflict exists as each member of a pair attempts to maximize its fitness, both sexes behave as though a major role of male vigilance is to enhance female foraging opportunities. Received: 3 May 1999 / Received in revised form: 14 June 1999 / Accepted: 16 June 1999     

Linking trophic positions and flow structure constraints in ecological networks: Energy transfer efficiency or topology effect?

In the present work we investigate whether the distribution of energy flows in ecosystems responds to criteria of trophic organization. We analyzed weighted and unweighted food webs estimating, for each node, trophic position (TP), Shannon's index of inflow diversity (H) and individual contribution to the whole average mutual information (AMI). Finally, we performed the same analysis on simulated webs that were constructed using the following criteria: (a) preserving topology and varying link strength; (b) modifying position of links and their intensities.     

Deterring predators, daunting opponents or drawing partners? Signaling rates across diverse contexts in the lizard Anolis sagrei

Although the visual display behavior in Anolis lizards has received ample attention, the function of dewlap extensions (DE), push-ups (PU), and head-nods (HN) in general, and in Anolis sagrei in particular, remains highly equivocal. Therefore, our primary goal was to quantify the display rates of these visual signal types (DE, PU, and HN) in a variety of contexts, using A. sagrei as study species. To our knowledge, this is the first study to test individuals of both sexes in a repeated-measures design across multiple contexts, including predator, non-predator and social interactions (mirror, male–male, male–female, female–male). We found that males have an overall higher signaling rate than females across all contexts. In addition, we found that lizards of both sexes exhibited higher display rates in the presence of conspecifics than when confronted with a predator or non-predator, suggesting that DE, PU, and HN function in intraspecific communication, not in predator deterrence. Whereas females did not significantly raise display rates in a consexual and heterosexual context with respect to subject-alone context, males did. The PU signal type only appears to play a major role for A. sagrei males during aggressive encounters. During heterosexual interactions, increased frequencies of all signal types suggest that DE, PU, and HN are essential for male courtship. Finally, we suggest that intersexual selection is probably a driving force for frequency-related dewlap use in both sexes. In contrast, pronounced intersexual differences were detected for PU and HN rates within a social context.     

When is increasing consumption of common property optimal? Sorting,congestion and entry in the commons

First-best pricing or assignment of property rights for rival and non-excludable goods is often infeasible. In a setting where the social planner cannot limit total use, we show that common-property resources can be over or under-consumed. This depends on whether the external benefits of reallocating users to less congested resources outweigh the additional costs imposed by new entrants. Importantly, we show that it may be optimal to encourage consumption of some common property resources. Our results have important implications for settings ranging from fisheries and forestry to recreational demand and transportation.     

Population viability of the Siberian Tiger in a changing landscape: Going, going and gone?

The Amur tiger (Panthera tigris altaica) is a flagship species of the boreal forest ecosystem in northeastern China and Russia Far East. During the past century, the tiger population has declined sharply from more than 3000 to fewer than 600 individuals, and its habitat has become much smaller and greatly fragmented. Poaching, habitat degradation, habitat loss, and habitat fragmentation have been widely recognized as the primary causes for the observed population decline. Using a population viability analysis tool (RAMAS/GIS), we simulated the effects of poaching, habitat degradation, habitat loss, and habitat fragmentation on the population dynamics and extinction risk of the Amur tiger, and then explored the relative effectiveness of three conservation strategies involving improving habitat quality and establishing movement corridors in China and Russia. A series of controlled simulation experiments were performed based on the current spatial distribution of habitat and field-observed vital rates. Our results showed that the Amur tiger population could be viable for the next 100 years if the current habitat area and quality were well-maintained, with poaching strictly prohibited of the tigers and their main prey species. Poaching and habitat degradation (mainly prey scarcity) had the largest negative impacts on the tiger population persistence. While the effect of habitat loss was also substantial, habitat fragmentation per se had less influence on the long-term fate of the tiger population. However, to sustain the subpopulations in both Russia and China would take much greater conservation efforts. The viability of the Chinese population of tigers would rely heavily on its connectivity with the largest patch on the other side of the border. Improving the habitat quality of small patches only or increasing habitat connectivity through movement corridors alone would not be enough to guarantee the long-term population persistence of the Amur tiger in both Russia and China. The only conservation strategy that allowed for long-term persistence of tigers in both countries required both the improvement of habitat quality and the establishment of a transnational reserve network. Our study provides new insights into the metapopulation dynamics and persistence of the Amur tiger, which should be useful in landscape and conservation planning for protecting the biggest cat species in the world.     

Are indigenous forest reserves sustainable? An analysis of present and future land-use trends in Bosawas,Nicaragua

SUMMARY

In recent years, indigenous tenure over forest lands has emerged as a means to conserve forests while recognizing indigenous rights. There is concern, however, that indigenous reserves may not be an appropriate policy tool for sustained forest conservation. Our research examined how recognition of indigenous common-property rights has controlled agricultural expansion and conserved forests in Bosawas Biosphere Reserve, Nicaragua. We used satellite imagery with empirical data gathered in the field on land-use institutions, population pressures, and land-use practices to compare whether indigenous communities under territorial management or public management are better able to (1) control the ‘fast threat’ of frontier expansion and (2) address the long-term ecological threats posed by indigenous land-use practices and institutional changes in the region. Our findings are that indigenous residents who share common-property rights over their territories are better able to control agricultural expansion than are indigenous residents living on public lands. With respect to the long-term threats to the region, a series of simulations of possible land-use pressures demonstrate that the enforcement of territorial boundaries and further development of indigenous forest management rules will prove crucial in determining land-use capacity and deforestation over the next 50 years.