Individual willingness to leave a safe refuge and the trade-off between food and safety: a test with social fish

Refuges offer prey animals protection from predation, but increased time spent hiding can reduce foraging opportunities. Within social groups, individuals vary in their refuge use and willingness to forage in the presence of a predator. Here, we examine the relative foraging benefits and mortality costs associated with individual refuge use and foraging behaviour within groups of goldfish (Carassius auratus) under predation risk from an avian predator (little egret-Egretta garzetta). We assessed individual order of emergence from the refuge and participation over 15 group foraging outings, and assigned each fish a daily outing index score. The individual fish that emerged from the refuge earlier than the other group members and that participated in more outings received high outing index scores and consumed more food compared with fish that tended to emerge in posterior positions and participate in fewer outings. However, individual fish that attained high outing index scores suffered a higher risk of predation. Furthermore, the amount of time the egret spent at the pool affected group foraging behaviour: as predation risk increased, groups of fish consumed significantly less food. Our results exemplify the trade-off between foraging success and safety from predation that prey species regularly experience.

Too much of a good thing? A landscape-of-fear analysis for collared peccaries (Pecari tajacu) reveals hikers act as a greater deterrent than thorny or bitter food

To study how wildlife perceive recreating humans, we studied the habitat selection of a human commensalist, the collared peccary (Pecari tajacu (Linnaeus, 1758)). We measured peccary activity patterns in an area of high human activity (Tumamoc Hill Desert Laboratory in Tucson, Arizona, USA) using a landscape-of-fear analysis. We examined whether the perception of risk from human activity interacted with the chemical (tannin) and mechanical (thorns) antipredator mechanisms of local plant species. The peccaries avoided food stations near a hiking trail. The population foraged less near houses, i.e., moderate human activity, than in the perceived safety of a small wadi. Plant defence treatments impacted the harvesting of food only in the safe zone, suggesting that risk trumps food selectivity. The strong effect of the hiking trail on habitat selection in this disturbance-loving species is an indicator of a much larger impact on sensitive species in conservation areas.

Comparing the non-lethal and lethal effects of predation risk ‬on goldfish anti-predatory behavior

Little egrets (Egretta garzetta) and common goldfish (Carassius auratus) interacted in experimental theaters that challenge them with a behavioral game. We studied the behavioral tactics of both players. The experimental theaters consist of three equally spaced pools, each with a shelter in its center. The fish can take shelter in a safe but foodless habitat, or swim exposed in the open that contains food. The egrets can move among the pools to catch the exposed fish. We investigated the importance of non-lethal effects versus lethal effects on predator–prey interactions. We created a variance in predation pressure by keeping the number of egrets fixed but varying the number of pools of the experimental theater between 1 and 3 pools. In all treatments, even when the egret was present, individual goldfish emerged from protected cover occasionally, exposing at least their heads and sometimes their entire bodies in apparent disregard for the possibly lethal consequences. We assumed that this behavior stems from the fish's constant need to collect information about its surroundings. The fish responded appropriately to the variations in predation pressure by changing their activity level outside the cover, i.e., the fish drastically and significantly reduced their exposure outside the cover, as well as the rate of peeping, as predation pressure increased. The results demonstrate the importance role of non-lethal effects, and how they drive the behavior of prey in response to predation risk, which in turn, drives the action of the predator in an asymmetric two-player game of stealth and fear.

Green roofs: new ecosystems to defend species diversity

Many contributions to the symposium seek to expand the role of green roofs in the conservation of biodiversity. Indeed, if green roofs can be harnessed for biodiversity, they will add area to that now available to nature. That would have the mass effect of increasing the sustainable number of species in simple conformity with the species--area relationship. Because all green roofs are novel ecosystems, all represent instances of reconciliation ecology, i.e., re-engineering human uses to permit simultaneous beneficial use by people and nature. Green roofs can provide a large number of experiments that might teach us how to improve their design. But those experiments, like any in science, must be overtly designed so that their hypotheses are clear and explicit, their methods repeatable, and their data appropriate for rigorous analysis. I present an embryonic example using native plant species growing at ground level in the urban environments of Tucson, AZ, USA. Steps include: (1) formulating a hypothesis; (2) developing a database of species' attributes to allow intelligent selection for hypothesis testing; (3) developing software to allow winnowing the list of species to sets with a good chance, according to the hypothesis, of growing together; (4) installing the sets of plants and measuring the results; (5) defining a continuous measure of conformity with the hypothesis; and (6) comparing results to hypothesis. If ecologists can successfully design reconciled ecosystems in urban settings – green roofs included – city people will be able to re-establish their everyday connection to nature.

Decoupling fragmentation from habitat loss for spiders in patchy agricultural landscapes

Habitat loss reduces species diversity, but the effect of habitat fragmentation on number of species is less clear because fragmentation generally accompanies loss of habitat. We compared four methods that aim to decouple the effects of fragmentation from the effects of habitat loss. Two methods are based on species-area relations, one on Fisher's alpha index of diversity, and one on plots of cumulative number of species detected against cumulative area sampled. We used these methods to analyze the species diversity of spiders in 2, 3.2 × 4 km agricultural landscapes in Southern Judea Lowlands, Israel. Spider diversity increased as fragmentation increased with all four methods, probably not because of the additive within-patch processes, such as edge effect and heterogeneity. The positive relation between fragmentation and species diversity might reflect that most species can disperse through the fields during the wheat-growing season. We suggest that if a given area was designated for the conservation of spiders in Southern Judea Lowlands, Israel, a set of several small patches may maximize species diversity over time.

The Life and Legacies of a Polymath Yale University Press, New Haven, CT, 2010. 475 pp. $40, £30. ISBN 9780300161380

Slack explores the many facets of the life and science of G. Evelyn Hutchinson and his fundamental contributions to modern ecology.

Habitat fragmentation may not matter to species diversity

Conservation biologists worry that fragmenting a bloc of natural habitat might reduce its species diversity. However, they also recognize the difficulty and importance of isolating the effect of fragmentation from that of simple loss of area. Using two different methods (species-area curve and Fisher's alpha index of diversity) to analyse the species diversities of plants, tenebrionid beetles and carabid beetles in a highly fragmented Mediterranean scrub landscape, we decoupled the effect of degree of fragmentation from that of area loss. In this system, fragmentation by itself seems not to have influenced the number of species. Our results, obtained at the scale of hectares, agree with similar results at island and continent scales.

The impact of long-term continuous risk of predation on two species of gerbils

Individuals of Gerbillus allenbyi Thomas, 1918 were subjected to artificial illumination in large field enclosures (2-ha sandy-substrate plots in the Negev Desert, Israel). The illumination was similar to that provided by a full moon and was used to mimic the elevated risk of avian predation that accompanies a full moon. We artificially illuminated the enclosures during all hours of darkness for 3 consecutive months. In some cases, we also added individuals of Gerbillus pyramidum Geoffroy, 1825 to provide a competitive challenge for the G. allenbyi. In the presence of the light source, individuals of G. allenbyi shifted their foraging activity to favor experimental areas of darkness. They also foraged less in the open and more beneath bushes. In the absence of the light source, G. allenbyi shifted its activity from the subplot with G. pyramidum to the subplot without the competitor. However, the competitive effect of the G. pyramidum disappeared in plots that were artificially illuminated. These results closely resemble those of earlier experiments during which we increased the apparent risk of predation in brief pulses lasting only 2 h/night.

Loss of speciation rate will impoverish future diversity

Human activities have greatly reduced the amount of the earth's area available to wild species. As the area they have left declines, so will their rates of speciation. This loss of speciation will occur for two reasons: species with larger geographical ranges speciate faster; and loss of area drives up extinction rates, thus reducing the number of species available for speciation. Theory predicts steady states in species diversity, and fossils suggest that these have typified life for most of the past 500 million years. Modern and fossil evidence indicates that, at the scale of the whole earth and its major biogeographical provinces, those steady states respond linearly, or nearly so, to available area. Hence, a loss of x% of area will produce a loss of about x% of species. Local samples of habitats merely echo the diversity available in the whole province of which they are a part. So, conservation tactics that rely on remnant patches to preserve diversity cannot succeed for long. Instead, diversity will decay to a depauperate steady state in two phases. The first will involve deterministic extinctions, reflecting the loss of all areas in which a species can ordinarily sustain its demographics. The second will be stochastic, reflecting accidents brought on by global warming, new diseases, and commingling the species of the separate bio-provinces. A new kind of conservation effort, reconciliation ecology, can avoid this decay. Reconciliation ecology discovers how to modify and diversify anthropogenic habitats so that they harbor a wide variety of species. It develops management techniques that allow humans to share their geographical range with wild species.

Safety in numbers: sophisticated vigilance by Allenby's gerbil

Since 1963, nonlinear predation theory has predicted that, at low population densities, victim species may well be mutualistic rather than competitive. Theory identifies this mutualism as a principal source of dynamic instability in the interaction. Using gerbils and trained barn owls, we conducted the first (to our knowledge) field tests of the theory's prediction of mutualism. The behavior of the gerbils confirms its existence.

Tilman's predicted productivity-diversity relationship shown by desert rodents

Tilman has developed a model to predict the number of plant species that can coexist competitively on a limited resource base. Species diversity first increases over low resource supplies, then declines as the environment becomes richer. Although Tilman 's model was developed to describe interspecific interactions between plant species, it may also apply to animal species. Tilman questions whether animals specialize on particular proportions of nutrients. However, we believe animals probably specialize on relatively subtle microhabitat differences, especially in a multispecies competitive regime. Thus, microhabitats may act like nutrients. We hypothesize that animal species, too, show a peaked curve of diversity over productivity. The present data provide a confirmation of the hypothesis using rodent species. We have investigated the number of rodent species along a geographical gradient of increasing rainfall. The gradient extends from extremely poor desert habitats to those with annual rainfall over 300 mm. Because of the aridity , precipitation reflects productivity. The diversity pattern in desert rodents agrees with that predicted by Tilman for plants. It even possesses similar asymmetry, rising steeply then falling slowly. The pattern is duplicated in rocky and sandy habitats, each of which has a distinct and almost nonoverlapping assemblage of species. As mean precipitation is closely correlated with the variability of precipitation, the diversity pattern might also be caused by a decline in the frequency of disturbances, models for which have been proposed by several investigators.