High-risk Habitats Research Articles

Increasing Residential Proximity of Lyme Borreliosis Cases to High-Risk Habitats: A Retrospective Study in Central Bohemia, the Czech Republic, 1987–2010

An analysis of historical data on Lyme borreliosis in Central Bohemia between 1987-2010 has revealed that the rate of peri-domestic exposure, the proximity of patients' residences to high-risk habitats, and the number of disease cases have been interdependent variables and that their common upturn can be dated back to the start of the 1990s or earlier. The data indicate that the disease rise is attributable to translocation of part of the at-risk population nearer to natural environments, rather than to mere intensification of people's peri-domestic exposure at existing residential locations, or changes in the natural environment itself.

Interindividual variability in habitat use: evidence for a risk management syndrome in roe deer?

The way an individual reacts to the risk of predation or disturbance may have important consequences for its immediate and future survival. Risk is likely perceived differently by individuals in relation to among-individual differences in correlated behavioral traits, that is, syndromes or personalities. Given that animals can avoid the risk of predation/disturbance through modification of their habitat use, we might expect individuals of differing behavioral types to adopt contrasting tactics of habitat use when faced with risky or stressful situations. We studied the relationship between habitat use and among-individual variation in behavioral profile in a population of roe deer. We hypothesized that an individual's habitat use tactics should be related to their capacity to cope with risky situations. In particular, we predicted that more reactive (risk-averse) roe deer, with relatively high behavioral response and high body temperature at capture, long flight distances and which were more vigilant during feeding, should use riskier open habitat less, particularly when risk is high. We found that although the use of open habitat during the day was negatively correlated with the indices of reactivity at capture, it was also positively correlated with indices of reactivity while foraging in open habitat. Furthermore, most of the behavioral parameters we measured were intercorrelated and moderately repeatable, potentially indexing personality traits. We conclude that there is substantial interindividual variability in how individuals manage risky situations which imposes constraints on how they are able to exploit high-risk habitats, suggesting the existence of a risk management syndrome in this large herbivore.

Plastic and Heritable Variation in Shell Thickness of the Intertidal Gastropod Nucella lapillus Associated with Risks of Crab Predation and Wave Action, and Sexual Maturation

The intertidal snail Nucella lapillus generally has thicker shells at sites sheltered from wave action, where crabs are abundant and pose a high risk of predation, than at exposed sites where crabs are rare. We studied two populations showing the opposite trend. We reciprocally transplanted snails between field sites and measured shell length, width and lip thickness of those recaptured 12 months later. Snails transplanted to the sheltered site grew larger than sheltered-site residents, which in turn grew larger than transplants to the exposed site. Relative shell-lip thickness was greater in residents at the exposed site than at the sheltered site. Transplants from shelter to exposure developed relatively thicker shells than their controls and relatively thinner shells from exposure to shelter. Progeny of the two populations were reared for 12 months in a common garden experiment presenting effluent from crabs feeding on broken conspecifics as the treatment and fresh sea-water as the control. The crab-effluent treatment decreased foraging activity, concomitantly reducing cumulative somatic growth and reproductive output. Juveniles receiving crab-effluent grew slower in shell length while developing relatively thicker shell lips than controls, the level of response being similar between lineages. F2 progeny of the exposed-site lineage showed similar trends to the F1s; sheltered-site F2s were too few for statistical analysis. At sexual maturity, shell-lip thickness was greater in snails receiving crab-effluent than in controls, indicating plasticity, but was also greater in the exposed-site than in the sheltered-site lineage, indicating heritable variation, probably in degree of sexual thickening of the shell lip. Results corroborate hypotheses that ‘defensive’ shell thickening is a passive consequence of starvation and that heritable and plastic control of defensive shell morphology act synergistically. Shell thickening of juveniles was similar between lineages, contrary to hypotheses predicting differential strengths of plasticity in populations from low- or high-risk habitats.

Intraspecific trait cospecialization of constitutive and inducible morphological defences in a marine snail from habitats with different predation risk

1. Studies examining the integration of constitutive and inducible aspects of multivariate defensive phenotypes are rare. 2. I asked whether marine snails (Nucella lamellosa) from habitats with and without abundant predatory crabs differed in constitutive and inducible aspects of defensive shell morphology. 3. I examined multivariate shell shape development of snails from each habitat in the presence and absence of waterborne cues from feeding crabs (Cancer productus). I also examined the influence of constitutive and inducible shell morphology on resistance to crushing. 4. Regardless of the presence of crabs, snails from high-risk (HR) habitats developed rotund, short-spired shells, while snails from low-risk habitats developed elongate shells, tall-spired shells, indicating among-habitat divergence in constitutive shell shape. Moreover, allometry analyses indicated that constitutive developmental patterns underlying this variation also differed between habitats. However, snails from HR habitats showed greater plasticity for apertural lip thickness and apertural area in the presence of crab cues, indicating among-habitat variation in defence inducibility. 5. Both shell shape and apertural lip thickness contributed to shell strength suggesting that constitutive shell shape development and inducible lip thickening have evolved jointly to form an effective defence in habitats where predation risk is high.

Influence of predation risk and food supply on nocturnal fish foraging distributions along a mangrove–seagrass ecotone

Diverse taxa from many systems must make tradeoffs between food and safety. How- ever, few studies have examined the response of multiple fish species to food and predation risk at night across their foraging landscape. In Biscayne Bay, Florida (USA), we investigated the influences of food and predation risk on nocturnal habitat use of gray snapper, bluestriped grunt and seabream along a distance gradient spanning from the mangrove-seagrass ecotone to 120 m offshore. Seine and submerged vegetation sampling were used to determine the distribution of fishes and their food resources. Tethering experiments were used to explore gradients in predator encounter rates. We used these data to test the following a priori predictions of fish distributions relative to food and risk as generated from foraging theory: (1) fishes will be distributed in proportion to their food supply (i.e. ideal free distribution, IFD); or (2) fishes will avoid high-risk areas such that their abundances will be lower than predicted by food resources in high-risk habitats (i.e. food-risk tradeoff). Results indi- cated that none of the fishes were distributed according to IFD. Seabream and gray snapper avoided foraging close to shore, where their food was abundant, but risk was highest. Bluestriped grunt responses to spatial variation in food supply and risk were less clear; they appeared to forage randomly across the distance gradient. Our results suggest that fish generally avoid the risky man- grove-seagrass ecotone, but responses to variation in food and risk are species-specific and may be dependent on specific anti-predator tactics or influenced by factors we did not measure.

Habitat selection for parasite‐free space by hosts of parasitic cowbirds

Choice of breeding habitat can have a major impact on fitness. Sensitivity of habitat choice to environmental cues predicting reproductive success, such as density of harmful enemy species, should be favored by natural selection. Yet, experimental tests of this idea are in short supply. Brown‐headed cowbirdsMolothrus atercommonly reduce reproductive success of a wide diversity of birds by parasitizing their nests. We used song playbacks to simulate high cowbird density and tested whether cowbird hosts avoid such areas in habitat selection. Host species that made settlement decisions during manipulations were significantly less abundant in the cowbird treatment as a group. In contrast, hosts that settled before manipulations started and non‐host species did not respond to treatments. These results suggest that hosts of cowbirds can use vocal cues to assess parasitism risk among potential habitat patches and avoid high risk habitats. This can affect community structure by affecting habitat choices of species with differential vulnerability.

Spatial patterns in a discrete-time SIS patch model

How do spatial heterogeneity, habitat connectivity, and different movement rates among subpopulations combine to influence the observed spatial patterns of an infectious disease? To find out, we formulated and analyzed a discrete-time SIS patch model. Patch differences in local disease transmission and recovery rates characterize whether patches are low-risk or high-risk, and these differences collectively determine whether the spatial domain, or habitat, is low-risk or high-risk. In low-risk habitats, the disease persists only when the mobility of infected individuals lies below some threshold value, but for high-risk habitats, the disease always persists. When the disease does persist, then there exists an endemic equilibrium (EE) which is unique and positive everywhere. This EE tends to a spatially inhomogeneous disease-free equilibrium (DFE) as the mobility of susceptible individuals tends to zero. The limiting DFE is nonempty on all low-risk patches and it is empty on at least one high-risk patch. Sufficient conditions for the limiting DFE to be empty on other high-risk patches are given in terms of disease transmission and recovery rates, habitat connectivity, and the infected movement rate. These conditions are also illustrated using numerical examples.

Population dynamics of epiphytic bromeliads: Life strategies and the role of host branches

Summary Epiphytes need to balance the trade-off between long-term survival and colonizing new branches in their resource-limited and high-risk canopy habitats. We censused populations of five bromeliad species over two years and calculated matrix population models to determine the key factors influencing population growth rates. Additionally, logistic regression models were applied to study how demographic features change with microsite characteristics and disturbance. The bromeliads studied are slow-growing, with species preferring thinner branches maturing faster. Population growth rates were below unity in all species except for the drought-resistant Tillandsia juncea. Population growth rates depended almost exclusively on survival, above all of adult plants. Fecundity had only little impact, even in species of the outer canopy where branchfall-related disturbance and mortality are frequent. Survival rates and the probability to become reproductive increased with light availability in most species. Microsite characteristics had the greatest impact on seedling survival, although this contributed very little to population growth rates. We conclude that branchfall-related mortality is a key factor for population persistence of epiphytes dwelling in the outer canopy, and that resource availability constrains the possibility to counteract disturbance with higher fecundity. For species of the outer canopy an increased disturbance by more frequent strong winds could further constrain population growth. Because population persistence strongly relies on the survival of adult plants, harvesting bromeliads for ornamental or other purposes should be restricted to immature individuals. In the future, better models of epiphyte populations in a habitat with highly patchily dynamics should be based on a metapopulation approach.

PATCH SHAPE, CONNECTIVITY, AND FORAGING BY OLDFIELD MICE (PEROMYSCUS POLIONOTUS)

We examined how corridors and patch shape affect foraging by the oldfield mouse (Peromyscus polionotus )b y deploying foraging trays and live traps in experimental landscapes with 3 different patch types: patches connected with a corridor, unconnected patches with projecting corridorlike portions (‘‘winged’’ patches), and unconnected rectangular patches. Corridors did not lead to different levels of activity of P. polionotus among the 3 patch types. Rather, corridors influenced activity by changing patch shape: foraging in seed trays and total number of captures of P. polionotus tended to be greater at the patch center than at the patch edge, but only in connected and winged patches where corridors or wings increased the amount of patch edge relative to the amount of core habitat in the patch. P. polionotus avoided open microhabitats near the patch edge in winged and connected patches, but not open microhabitats near the patch interior, suggesting that predation risk caused shifts in foraging near edges in connected and winged patches. Foraging in corridors and wings was generally low, suggesting that both are high-risk habitats where predation risk is not ameliorated by proximity to vegetative cover. By changing patch shape, corridors caused changes in within-patch activity of P. polionotus, changing foraging patterns and potentially altering the dynamics of P. polionotus and the seeds they consume.

Tick-borne encephalitis virus prevalence in Ixodes ricinus ticks collected in high risk habitats of the south-Bohemian region of the Czech Republic.

A survey for tick-borne encephalitis virus in trades ricinus ticks was conducted in May 2000 in two districts of the South-Bohemian region of the Czech Republic with a high occurrence of tick-borne encephalitis (TBE) in humans. Homogenized ticks were tested on PS cells, which were examined for any cytopathic effect, plaque assay and indirect fluorescent antibody test (IFT). The IFT has proved to be the most sensitive and most rapid test to demonstrate the virus in ticks. TBE virus was found in 17 of 187 pooled samples. consisting of a total of 2,968 ticks. The mean minimum infection rate was 0.6% for all tick stages combined. Infection rates in nymphs collected in different locations varied between 0.2 and 1.3% and between 5.9 and 11.1% in adult ticks. The observed TBE prevalence in ticks was compared with data obtained elsewhere in the Czech Republic. It is concluded that screening of ticks for TBE virus prevalence using IFT is a valuable indicator for the degree of risk to contract TBE in as particular habitat.

Refuge use and predation risk in a desert baboon population

Baboons face a serious threat of predation from leopards,Panthera pardusand lions,Panthera leoSince trees and cliff faces provide safety from these predators, baboons might use such refuges in order to reduce predation risk. This hypothesis was explored in a study of four groups of chacma baboons,Papio cynocephalus ursinusin a desert population in Namibia (groups ranged between 22 and 55 individuals with one to six adult males). All baboons spent most of their time close by refuges and little time distant from them. This pattern was most accentuated among females in smaller groups. These females spent more time on refuges primarily as a result of greater refuge use during resting and grooming. This pattern was less clear during feeding and travelling, apparently owing to the constraints on refuge use imposed by the nature of these activities. A comparison of refuge use in high-risk and low-risk habitats (after the confounding effects of habitat-specific refuge availability had been removed) suggests that baboons might adopt one of two strategies in high-risk areas; if refuges are widespread they will use refuges more intensively, but if refuges are scarce they will adopt a time-minimizing strategy to leave the area as rapidly as possible. The baboons also increased their vigilance when refuges were distant. These results are consistent with the hypothesis that baboons use refuges to reduce predation risk.

Fathead minnows (Pimephales promelas) learn to recognize chemical stimuli from high-risk habitats by the presence of alarm substance

We exposed fathead minnows (Pimephales promelas) to water from one of two distinct habitat types (an open water site or a vegetated cover site in the same stream) that we mixed with either alarm substance or a distilled water control. Upon subsequent exposures to the habitat waters alone, minnows showed a fright response to the habitat water that they received in conjunction with alarm substance but not to the other habitat water. These results indicate that minnows can learn to recognize high-risk habitats based on the association of habitat specific chemical cues with alarm substance. The ability to recognize these habitats could potentially lower the minnows' risk of predation. These results provide evidence of a long-term benefit to receivers of a chemical alarm signal.

Parental provisioning and predation risk in rhinoceros auklets (Cerorhinca monocerata): effects on nestling growth and fledging

Anne Harfenist Ronald C Ydenberg Behavioural Ecology Research Group, Department of Biological Science*, Simon Fra*er University, Bumaby, British Columbia V5A 1S6, Canada We examined the effects of predation risk on the behavior of rhinoceros auklets (Cerorhinca monocerata) breeding at Pine Island, British Columbia, in 1990. Provisioning parents in some areas of the colony risked predation by bald eagles (Haliatttus leucocephahu). Chicks in high and low predation risk areas of the colony hatched on approximately the same date, received similar amounts of food to 46 days of age, grew at the same rate, reached similar peak masses, and fledged at similar masses. However, chicks in high predation areas fledged at a younger age than did chicks in low predation areas. These data are consistent with the hypothesis that parents in high risk areas terminated provisioning several days before those in lower risk areas. Mass at fledging was inversely related to age at fledging in both high and low risk areas. The regression line for the high risk habitats lies below that from the low risk habitats, as predicted by a model that examines optimal time of fledging from the perspective of the parents. We conclude that risk of predation represents a significant cost of reproduction to some rhinoceros auklets and that individual auklets within the colony vary their behavior according to predation risk.

Plant-specific expression of antipredator behaviour by larval damselflies

In this study of interactions between larval damselflies (Zygoptera: Coenagrionidae) and pumpkinseed sunfish (Lepomis gibbosus) we focus on the behaviour of the damselfly prey. First we document a prey behaviour in which damselflies use plant stems or leaves to hide from pumpkinseeds. We then test two hypotheses: (1) that damselfly 'hiding' is a specific antipredator behaviour and (2) that 'hiding' occurs more frequently in plant habitats where damselflies experience greater risk of predation. Since plant species growth forms can influence predation risk, our second hypothesis implies that hiding behaviour is conditional upon the type of vegetation providing habitat structure. Conditional expression of antipredator behaviour according to vegetation type may be important in littoral environments, since predator-prey interactions can occur in habitats with a wide range of macrophyte growth forms. The first hypothesis was supported by our findings that damselfly hiding increased in frequency in the presence of pumpkinseeds, that it was related to the frequency of predator approaches, and that its use reduced damselfly predation risk in high risk habitats. The second hypothesis was supported by our results that damselfly hiding rates were greater in the high risk Scirpus habitats than in the lower risk Potamogeton habitats. These results indicate that prey behaviour can influence predator-prey interactions, and that variation in plant growth form can influence prey behaviour, thus contributing to the impact of habitat structure on predator-prey dynamics.