The effect of patch constellation on the exchange of individuals between habitat-islands

Metapopulation models assume that inter-patch dispersal dominantly depends on distance between patches and the dispersal capability of organisms in question. We used a spatially explicit, individual-based model to investigate the potential effect of patch constellation on the exchange of individuals between patches. We simulated migration of individuals from a start- into a target-patch with both patches having the same size and shape. Simulation experiments were carried out for four patch constellations and two different movement patterns. Our results demonstrate a substantial effect of patch constellation on the exchange of individuals. They also show that the magnitude and even the direction of this effect crucially depends on their movement pattern. We conclude that particularly for highly correlated movement patterns patch shape and constellation can not readily be ignored when modelling inter-patch dispersal between habitat-islands.     

Loss of mating opportunities influences refuge use in the Iberian rock lizard,<Emphasis Type="Italic"> Lacerta monticola</Emphasis>

Because time spent in refuge may be costly if prey lose opportunities to forage, fight, or mate, prey allow predators to approach closer before beginning to flee when opportunity costs are high. Because the same opportunity costs may apply to refuge use as to escape, prey should make similar trade-offs between risk of emerging and cost of remaining in refuge. In the Iberian rock lizard, Lacerta monticola, we studied the effects of sex, reproductive season, speed of predator approach, and potential loss of mating opportunities on time spent in refuge following simulated predatory attacks. Lizards of both sexes adjusted refuge use to the level of risk by spending more time in refuge when approached rapidly than slowly. Females remained in refuge for equal times in the mating and postreproductive seasons, but males emerged sooner during the mating season, suggesting adjustment to a cost of lost opportunity to search for mates during the mating season. When a tethered female was nearby, males emerged from refuge earlier than if no female was present, indicating a trade-off between risk and mating opportunity. Approach speed affected emergence time when females were absent, but not when a female was present. Approach speed did not affect the probability that, after emerging, a male would return to court the female. For males that courted females intensely (bit them) before entering refuge, approach speed did not affect latency to emerge, but males that courted less intensely emerged sooner if approached slowly than rapidly. These findings show that males adjust the length of time spent in refuge to both risk of predation and reproductive cost of refuge use.Communicated by A. Mathis     

Predation risk and foraging behavior of the hoary marmot in Alaska

Summary I observed hoary marmots for three field seasons to determine how the distribution of food and the risk of predation influenced marmots' foraging behavior. I quantified the amount of time Marmota caligata foraged in different patches of alpine meadows and assessed the distribution and abundance of vegetation eaten by marmots in these meadows. Because marmots dig burrows and run to them when attacked by predators, marmot-toburrow distance provided an index of predation risk that could be specified for different meadow patches.Patch use correlated positively with food abundance and negatively with predation risk. However, these significant relationships disappeared when partial correlations were calculated because food abundance and risk were intercorrelated. Using multiple regression, 77.0% of the variance in patch use was explained by a combination of food abundance, refuge burrow density, and a patch's distance from the talus where sleeping burrows were located. Variations in vigilance behavior (look-ups to search for predators while feeding) according to marmots' ages, the presence of other conspecifics, and animals' proximity to their sleeping burrows all indicated that predation risk influenced foraging.In a forage-manipulation experiment, the use of forage-enhanced patches increased six-fold, verifying directly the role of food availability on patch used. Concomitant with increased feeding, however, was the intense construction of refuge burrows in experimental patches that presumably reduced the risk of feeding. Thus, I suggest that food and predation risk jointly influence patch use by hoary marmots and that both factors must be considered when modeling the foraging behavior of species that can be predator and prey simultaneously.     

Manipulation of nest-box density affects extra-pair paternity in a population of blue tits (<Emphasis Type="Italic">Parus caeruleus</Emphasis>)

We tested the effect of manipulation of breeding density on the occurrence of extra-pair paternity in a blue tit (Parus caeruleus) population during two consecutive years. In a homogeneous oak forest, nest-box manipulation provided a high density plot (plot A, 1.10 and 1.32 pairs/ha) and a low density plot (plot B, 0.43 and 0.46 pairs/ha). Microsatellite analysis on 91 broods revealed a higher proportion of extra-pair paternity in broods in plot A (mean of 17.2%) than in plot B (mean of 11.4%). A correlative approach showed that the proportion of extra-pair young in broods was affected by the number of breeding neighbours within 100 m around the nest-box, by the distance to the nearest breeding neighbour and by an additional plot effect. However, the nearest neighbours accounted for only 39.3% of extra-pair paternities and distance to extra-pair fathers was significantly higher than the nearest neighbour distance in both plots. This implies that the effect of density on the occurrence of extra-pair paternities is associated with active female choice to enhance the brood fitness. Although there were more extra-pair young in broods when density was high, the number of extra-pair fathers did not increase and stayed close to one. We suggest that density increases the cost of mate guarding by males, thereby increasing the possibility for females to solicit extra-pair paternities to the cuckolding male they have chosen. Finally, we discuss why correlatives approaches do not always show evidence for an effect of breeding density on extra-pair paternity occurrence.Communicated by M. Soler     

Movement of foraging Tundra Swans explained by spatial pattern in cryptic food densities

We tested whether Tundra Swans use information on the spatial distribution of cryptic food items (below ground Sago pondweed tubers) to shape their movement paths. In a continuous environment, swans create their own food patches by digging craters, which they exploit in several feeding bouts. Series of short (<1 m) intra-patch movements alternate with longer inter-patch movements (>1 m). Tuber biomass densities showed a positive spatial auto-correlation at a short distance (<3 m), but not at a larger distance (3-8 m). Based on the spatial pattern of the food distribution (which is assumed to be pre-harvest information for the swan) and the energy costs and benefits for different food densities at various distances, we calculated the optimal length of an inter-patch movement. A swan that moves to the patch with the highest gain rate was predicted to move to the adjacent patch (at 1 m) if the food density in the current patch had been high (>25 g/m2) and to a more distant patch (at 7-8 m) if the food density in the current patch had been low (<25 g/m2). This prediction was tested by measuring the response of swans to manipulated tuber densities. In accordance with our predictions, swans moved a long distance (>3 m) from a low-density patch and a short distance (<3 m) from a high-density patch. The quantitative agreement between prediction and observation was greater for swans feeding in pairs than for solitary swans. The result of this movement strategy is that swans visit high-density patches at a higher frequency than on offer and, consequently, achieve a 38% higher long-term gain rate. Swans also take advantage of spatial variance in food abundance by regulating the time in patches, staying longer and consuming more food from rich than from poor patches. We can conclude that the shape of the foraging path is a reflection of the spatial pattern in the distribution of tuber densities and can be understood from an optimal foraging perspective.     

Body size and reserve protection affect flight initiation distance in parrotfishes

Flight initiation distance (FID), the distance at which an organism begins to flee an approaching threat, is an important component of antipredator behavior and a potential indicator of an animal’s perception of threat. In a field study on parrotfishes, we tested the predictions that FID in response to a diver will increase with body size, a correlate of reproductive value, and with experience of threat from humans. We studied a broad size range in four species on fringing reefs inside and outside the Barbados Marine Reserve. We used the Akaike's Information Criterion modified for small sample sizes (AICc) and model averaging to select and assess alternative models. Body size, reserve protection, and distance to a refuge, but not species, had strong support in explaining FID. FID increased with body size and generally remained two to ten times fish total length. FID was greater outside the reserve, especially in larger fish. Although we were not able to completely rule out other effects of size or reserve, this study supports predictions of an increase in FID with reproductive value and threat from humans.     

Do mountain log skinks (<Emphasis Type="Italic">Pseudemoia entrecasteauxii</Emphasis>) modify their behaviour in the presence of two predators?

Prey often adopt antipredator strategies to reduce the likelihood of predation. In the presence of predators, prey may use antipredator strategies that are effective against a single predator (specific) or that are effective against several predators (nonspecific). Most studies have been confined to single predator environments although prey are often faced with multiple predators. When more than one predator is present, specific antipredator behaviours can conflict and avoidance of one predator may increase vulnerability to another. To test how prey cope with this dilemma, I recorded the behaviours of lizards responding to the nonlethal cues of a bird and snake presented singly and simultaneously. Lizards use specific and conflicting antipredator tactics when confronted with each predator, as evidenced by refuge use. However, when both predators were present, lizards refuge use was the same as in the predator-free environment, indicating that they abandoned refuge use as a primary mechanism for predator avoidance. In the presence of both predators, they reduced their overall movement and time spent thermoregulating. This shift in behaviour may represent a compromise to minimize overall risk, following a change in predator exposure. This provides evidence of plasticity in lizard antipredator behaviour and shows that prey responses to two predators cannot be accurately predicted from what is observed when only one predator is present.Communicated by W. Cooper     

Pursuit deterrence,predation risk,and escape in the lizard <Emphasis Type="Italic">Callisaurus draconoides</Emphasis>

The frequency of pursuit-deterrent signaling should vary with predation risk for factors affecting decisions to flee and hide. Distance to refuge, temperature, and microhabitat types affect risk, and their effects may differ among defenses. Because risk is greater farther from refuge and at lower temperatures that impair escape ability in ectotherms, I predicted that when farther from refuge ectothermic prey flee sooner, enter refuge more frequently, and signal more frequently. At low temperatures, prey should flee sooner, enter refuge, and signal less frequently. Because signaling sometimes deters attack, lowered risk might allow prey to permit closer approach when signaling. In the zebra-tailed lizard Callisaurus draconoides, which signals by waving its tail, signaling and the other behaviors were affected by the same risk factors. Probability of signaling before fleeing increased with distance to refuge and temperature, but variation in temperature accounted for the effect of distance to refuge. Lizards signaled not at all at low temperatures, after starting to flee at intermediate temperatures, and before, during, and after fleeing at higher temperatures. This pattern is consistent with honest signaling of escape ability. Refuge entry was more frequent nearer refuge (lower risk) and at lower temperature (higher risk). Display was less frequent on rock than ground, possibly due to conspicuousness or delay in attaining high speed. Flight initiation distance was shorter after signaling. This novel finding suggests that signaling reduces risk and prey alter escape decisions based on lower risk as a consequence of their own signaling behavior.     

Traplining by purple-throated carib hummingbirds: behavioral responses to competition and nectar availability

We examined the effects of nectar availability and competition on foraging preferences and revisit intervals of traplining female purple-throated caribs hummingbirds (Eulampis jugularis) to Heliconia patches shared by two individuals or visited solely by one individual. Birds at both shared and solitary patches preferred multiflowered to single-flowered inflorescences, but the magnitude of this preference depended on food availability and competition. During a year of low flower availability, females visited multiflowered inflorescences more frequently than single-flowered inflorescences only when nectar availability was experimentally enhanced; similarly, females at shared patches exhibited a significant preference for multiflowered inflorescences only after experimental increases in nectar availability. Experimental manipulations of nectar availability also had different effects on revisit intervals of birds at shared vs solitary patches. Birds at shared patches responded to patch-wide increases in nectar rewards by increasing the duration of their visit intervals, whereas birds at solitary patches did not. In contrast, birds at solitary patches responded to abrupt losses of nectar at flowers (simulating competition) by decreasing the duration of their visit intervals, whereas a bird at a shared patch did not alter its return interval. The contrasting results between shared vs solitary patches suggest that future studies of traplining behavior should incorporate levels of competition into their design.     

Pyrrolizidine alkaloid content in <Emphasis Type="Italic">Senecio</Emphasis>: ontogeny and developmental constraints

Summary. The ontogeny of pyrrolizidine alkaloid (PA) synthesis and constraints on defence level during the seedling stage were examined in the annual Senecio vulgaris and the monocarpic perennial Senecio jacobaea. In both species, PAs were actively synthesized from the onset of seedling growth so that juvenile stages did not go through an undefended stage. Roots are known to be the exclusive sites where PAs are produced. Root biomass was the single most important biomass parameter explaining variation in total PAs per seedling. All correlation coefficients between—relative growth rate and PA concentration were negative, but none was significant. However, a significant negative—correlation was found between shoot to root ratio and PA concentration in S. jacobaeaseedlings, suggesting a dilution effect of the PAs. Earlier studies have shown that the shoot to root ratio is positively correlated with relative growth—rate of established S. jacobaea plants. It is therefore suggested that young S. jacobaea plants with a high shoot to root ratio and hence a high growth capacity necessarily have lower PA defence levels than plants with a low shoot to root ratio. Received 10 July 2002; accepted 16 November 2002.     

Behavioral response to predators reverses the outcome of competition between prey species

Summary In a laboratory experiment it was shown that piscivorous predators reversed the outcome of competitive interactions between two fish prey species, juveniles of roach (Rutilus rutilus) and perch (Perca fluviatilis), by behaviorally affecting their use of two available habitats, an open water habitat and a structurally complex refuge. The shift in the competitive relationship was the result of predators forcing the juvenile fishes into a prey refuge with high structural complexity. While roach was competitively superior in the unstructured habitat, perch was superior in the structurally complex prey refuge. The reversal in competitive relationship was demonstrated both with respect to foraging rate and growth rate and resulted from the high structural complexity in the prey refuge interfering with the roach's swimming performance. Because survival and growth patterns through the juvenile stages have profound effects on the population/community dynamics of size-structured populations such as those of fish, behaviorally induced changes in competitive ability should have significant implications also at the population and community levels.     

Dominance status influences female reproductive strategy in a territorial African rodent <Emphasis Type="Italic">Rhabdomys pumilio</Emphasis>

Dominance status influences the fitness of many mammals. Using African striped mice Rhabdomys pumilio, we tested whether (1) dominant females have greater reproductive success than subordinate females, (2) dominant females influence the reproductive output of subordinate females when they are housed in close proximity, (3) reproductive output of a female changes in response to the dominance status of her neighbours, and (4) whether prolonged association between individuals influences the variance in reproductive success between dominants and subordinates (i.e. the ‘dear enemy’ phenomenon). The size and mass of litters of dominants increased significantly when housed adjacent to subordinates than when housed apart. The litter size and mass of subordinates remained unchanged, although subordinates spent significantly more time with their pups when housed close to dominants than when housed apart; time spent with pups by dominants remained unchanged. Moreover, females modified their reproductive output and behaviour in relation to the dominance status of their neighbours. Following prolonged association, dominants still had greater reproductive success, but now, the time spent with pups decreased in subordinates. We suggest that dominants adopt a strategy to increase the reproductive value of their litter, whereas subordinates adopt a pup defence strategy. These strategies are flexible and are influenced by the dominance status and period of association between neighbours, so that females could maximize their fitness in response to varying social conditions.     

Subhabitat selection by foraging threespine stickleback (<Emphasis Type="Italic">Gasterosteus aculeatus</Emphasis>): previous experience and social conformity

Any mechanism that allows animals to increase their foraging efficiency is likely to be selected for, including the ability to learn to recognise and subsequently discriminate between habitat types based on their profitability. In a series of laboratory studies, we manipulated prey densities across two different experimental subhabitats and demonstrated that threespine stickleback (Gasterosteus aculeatus) can develop foraging preferences for subhabitats that have previously yielded prey. Fish were not recalling the spatial location of prey patches; rather, they were discriminating between subhabitats based on foraging experience there and allocating foraging effort accordingly. Foraging preferences took around 14 days to develop, and once established, they persisted independently of experimental prey density, suggesting that fish were using experience rather than real-time sampling to select foraging grounds. When we presented focal fish with social information cues, we found that they preferentially used local enhancement and current public information cues when they conflicted with previous experience, but that they did not use prior public information. This suggests that in the presence of conspecifics, individuals prioritise social conformity over the use of private information. We discuss our results in the context of optimal foraging and the trade-offs associated with balancing conflicting private and social information.     

How temperature and habitat quality affect parasitoid lifetime reproductive success—A simulation study

Adult parasitoid females lay their eggs in or on host insects. Most species are incapable of de novo lipogenesis as adults, and lipids accumulated during the larval stage are allocated either to egg production or to adult survival. Lipid consumption increases with distance covered by the parasitoids and thus with the distance between available hosts within a habitat. Temperature should affect parasitoid fitness because it changes the constraint imposed by a limited reserve of lipids and because it influences behaviour. Climate change involves both an increase in average temperature and an increased frequency of extreme weather such as heat waves. We investigated how the predicted increase of temperature will affect parasitoid fitness and how this depends on habitat parameters (spatial distribution of hosts and lipid cost of habitat exploitation). We studied optimal behaviour and calculated fitness at different temperatures and in different habitats using a stochastic dynamic programming model for pro-ovigenic parasitoids (which mature all their eggs before becoming adult). We show that an increase in temperature decreases fitness of parasitoids adapted to lower temperatures. This decrease in fitness depends on habitat quality. In field conditions (assuming small costs of intra-patch foraging), the loss of fitness should be larger in habitats with high inter-patch distance and in habitats with a more aggregated distribution of hosts. The foraging behaviour of parasitoids is also affected; at higher temperature we show that intra-patch foraging becomes less efficient, and patch residence times are longer.     

The hypoxia avoidance behaviour of juvenile Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis> L.) depends on the provision and pressure level of an O<Subscript>2</Subscript> refuge

The frequency of low O₂ (hypoxia) has increased in coastal marine areas but how fish avoid deleterious water masses is not yet clear. To assess whether the presence and oxygen pressure (PO₂) level of an O₂ refuge affects the hypoxia avoidance behaviour of fish, individual Atlantic cod (Gadus morhua L.) were exposed to a range of O₂ choices in a 2-way choice chamber at 11.4°C over two different experiments. Cod in the first experiment were allowed access to a fixed O₂ refuge (fully air-saturated seawater) whilst oxygen pressure (PO₂) on the other side was reduced in steps to a critically low level, i.e. 4.3 kPa—a point where cod can no longer regulate O₂ consumption. Under these conditions, cod did not avoid any level of hypoxia and fish swimming speed also remained unchanged. In contrast, strong avoidance reactions were exhibited in a second experiment when fish were again exposed to 4.3 kPa but the safety, i.e. PO₂, of the refuge was reduced. Fish not only spent less time at 4.3 kPa as a result of fewer sampling visits but they also swam at considerably slower speeds. The presence of an avoidance response was thus strongly related to refuge PO₂ and it is unlikely that cod, and possibly other fish species, would enter low O₂ to feed in the wild if a sufficiently safe O₂ refuge was not available. It is therefore hypothesized that the feeding range of fish may be heavily compressed if hypoxia expands and intensifies in future years.     

Defended versus undefended home range size of carnivores,ungulates and primates

Summary We tested the hypothesis that undefended home ranges are larger than defended home ranges using data collected from the literature for three groups of mammals. A matched-pairs analysis of populations within species or species within genera showed that undefended home ranges were larger than defended home ranges for carnivores and male ungulates, but not for primates. Primates may have been an exception because they violated a key assumption of the hypothesis, that defence costs increase with the size of the defended area. Undefended home ranges were 5.4 and 15.2 times larger than defended home ranges for carnivores and male ungulates, respectively. Whether or not a home range is defended is an important source of variation that should be included in future studies of home range size. Correspondence to: J.W.A. Grant     

Female choice over short and long distances: neighbour effects

Fiddler crabs live at high densities and mate-searching females encounter many males at varying distances. Who is the ideal neighbour for a male? There could be a trade-off if having neighbours that invest more in sexual signals increases the rate at which females initially move towards a focal male, but thereafter decrease the likelihood that he is chosen rather than his neighbour. We used robotic crabs to test whether female choice for focal males (identical claw size/courtship wave rate) varied depending on the relative investment in sexual signals of their two neighbours and the distance at which she first saw the males. The neighbours’ phenotype did not affect which of two focal males she initially approached from long-range (50 cm). When a female initially saw a trio of males at a close-range (20 cm), she preferentially chose the focal male over neighbours that invested less in sexual signals (smaller claw/slower wave rate), but did not show a preference for the focal male over neighbours that invested more in sexual signals (larger claw/faster wave rate). However, a female that started to approach a focal male with neighbours that invest more in sexual signals from 50 cm was significantly less likely to choose the focal male than when she first saw the trio at 20 cm. Our results suggest that the initial distance at which males are seen partly determines how neighbours’ sexual signals affect male mating success. In general, if larger males can retain smaller neighbours they might therefore increase their mating success.     

A Meta‐Analytic Review of Corridor Effectiveness

Abstract: Using corridors for conservation is increasing despite a lack of consensus on their efficacy. Specifically, whether corridors increase movement of plants and animals between habitat fragments has been addressed on a case‐by‐case basis with mixed results. Because of the growing number of well‐designed experiments that have addressed this question, we conducted a meta‐analysis to determine whether corridors increase movement; whether corridor effectiveness differs among taxa; how recent changes in experimental design have influenced findings; and whether corridor effectiveness differs between manipulative and natural experiments. To conduct our meta‐analysis, we analyzed 78 experiments from 35 studies using a conservative hierarchical Bayesian model that accounts for hierarchical and sampling dependence. We found a highly significant result that corridors increase movement between habitat patches by approximately 50% compared to patches that are not connected with corridors. We found that corridors were more important for the movement of invertebrates, nonavian vertebrates, and plants than they were for birds. Recent methodological advances in corridor experiments, such as controlling for the area added by corridors, did not influence whether corridors increased movement, whereas controlling for the distance between source and connected or unconnected recipient patches decreased movement through corridors. After controlling for taxa differences and whether studies controlled for distance in experimental design, we found that natural corridors (those existing in landscapes prior to the study) showed more movement than manipulated corridors (those created and maintained for the study). Our results suggest that existing corridors increase species movement in fragmented landscapes and that efforts spent on maintaining and creating corridors are worthwhile.     

Structure and function of the eversible glands of the aquatic firefly <Emphasis Type="Italic">Luciola leii</Emphasis> (Coleoptera: Lampyridae)

Summary. When attacked or otherwise disturbed, larvae of the aquatic firefly Luciola leii display fork-shaped glands laterally from the meso- and metathorax as well as each abdominal segment. Glandular eversion is accompanied by a strong pine oil-like odour, thanatosis and glowing from paired larval light organs. Observations by SEM and TEM revealed that there are numerous, almost spherical protuberances, measuring 9 μm in diameter on the surface of each gland. Each protuberance is connected to a well developed secretory cell via a 0.1 μm thick and 0.2 μm long stalk and bears three to six 7 μm long spines on its apex. The convoluted glandular walls measure 0.2 μm. The cytoplasm of the secretory cells is characterized by the presence of numerous mitochondria and an extensive system of cisternae and tubular endoplasmic reticulum. Preliminary GC-MS analysis of the glandular secretion revealed two volatile terpenoids: terpinolene and γ-terpinene. Choice and no-choice bioassays involving fish and ants as well as other predators demonstrate that the secretions serve as an effective deterrent against a range of ecologically relevant enemies. The larval postural adjustments, light emission, everted glands, and glandular release of distasteful or repellent compounds, appear to function as a multi-modal, aposematic larval defence. The tandem evolution of glandular secretions and conspicuousness in larval fireflies could partially explain their successful radiation into both aquatic and terrestrial habitats.     

Volatile substances in the pygidial secretion of gyrinid beetles (Coleoptera: Gyrinidae)

Summary Gyrinid beetles are common in freshwater habitats. They have paired pygidial glands with a secretion that contains high molecular weight substances rendering them toxic for predatory fish. In this paper we report on a laboratory study on volatile components released by three different gyrinid species when irritated. The volatile pattern had a clear difference between the different species.Gyrinus substriatus andG. aeratus, both produced 3-methyl-1-butanal and 3-methyl-1-butanol when irritated, but in quite different amounts. The third tested species,G. minutus, did not produce any substances above the detection level. It is suggested that the volatile compounds may be part of the beetles' communication and/or defence system.