Refuge Quality Research Articles

A stage-structured stochastic model of the population dynamics of Triatoma infestans, the main vector of Chagas disease

We present a stage-structured mathematical model of the population dynamics of Triatoma infestans in a single house, as part of a more complex model incorporating domestic Trypanosoma cruzi transmission. Novel features of this model are a formulation in continuous time accounting for demographic stochasticity, temperature-dependent female fecundity and developmental times, and insect stage-dependent host irritability. The model assumes a closed domestic insect population regulated by insect density and stage-dependent host irritability depressing the insects’ feeding success and female fecundity. The model describes that the abundance of T. infestans insects fluctuates seasonally with only one peak in summer, whereas eggs show one peak in spring and another in the fall as a result of two peaks in female fecundity. The proportion of recently fed adult insects peaks in summer and falls close to zero in winter only when the intensity of host irritability differs markedly between small and large insect stages. In our model, the insect carrying capacity is the joint result of density-dependent access to hosts and density-independent mortality rates. Our hypothesis is that refuge quality in the house, not the absolute number of refuges, determined by construction features would translate into differential insect stage mortalities. The presence of only one hen brooding indoors during spring and summer increases insect numbers in a clearly detectable way. Sensitivity analysis showed strong effects on timed-averaged insect abundance of prolonged developmental time induced by low temperatures, the threshold insect density for host irritability, and mean female fecundity.

A plant pathogen reduces the enemy–free space of an insect herbivore on a shared host plant

An important mechanism in stabilizing tightly linked host-parasitoid and prey-predator interactions is the presence of refuges that protect organisms from their natural enemies. However, the presence and quality of refuges can be strongly affected by the environment. We show that infection of the host plant Silene latifolia by its specialist fungal plant pathogen Microbotryum violaceum dramatically alters the enemy-free space of a herbivore, the specialist noctuid seed predator Hadena bicruris, on their shared host plant. The pathogen arrests the development of seed capsules that serve as refuges for the herbivore's offspring against the specialist parasitoid Microplitis tristis, a major source of mortality of H. bicruris in the field. Pathogen infection resulted both in lower host-plant food quality, causing reduced adult emergence, and in twofold higher rates of parasitism of the herbivore. We interpret the strong oviposition preference of H. bicruris for uninfected plants in the field as an adaptive response, positioning offspring on refuge-rich, high-quality hosts. To our knowledge, this is the first demonstration that plant-inhabiting micro-organisms can affect higher trophic interactions through alteration of host refuge quality. We speculate that such interference can potentially destabilize tightly linked multitrophic interactions.

Size-Specific Differences in Tail Loss and Escape Behavior in Liolaemus nigromaculatus

Facultative tail loss (autotomy) is a common and widespread antipredation adaptation in lizards (Arnold, 1988; Zani, 1996). Although offering an escape from predators, tail loss has been demonstrated to influence many life-history traits and to have fitnessrelated ecological and behavioral correlates (e.g., Martin and Avery, 1998; Wilson and Booth, 1998; Martin and Lopez, 2000, and references therein). Animals with autotomized tails also may have reduced abilities to escape predators (Dial and Fitzpatrick, 1984). Costs and benefits of tail autotomy have been discussed for many taxa, but these studies encompass only a small percentage of species employing this tactic, and further studies are critical to evaluate the generality of these observations. Theoretical models of escape behavior predict that animals will adjust the distance at which they flee from an approaching predator (fleeing distance) according to the relative costs of staying put versus the costs of fleeing (Ydenberg and Dill, 1986). When the former cost exceeds the latter, over any distance, the animal should seek refuge. A number of factors are known to influence the decision to stay put, including both intrinsic (e.g., age) and extrinsic factors such as predator characteristics, ambient temperature, distance and quality of available refuges, etc. (e.g., Rocha and Bergallo, 1990; Martin and L6pez, 1995, 2000; Cooper, 1997). Costs associated with fleeing are predominantly missed opportunity costs associated with abandoning a food resource, but for ectotherms may also include metabolic costs such as reduced time spent basking in the sun. Although several authors have evaluated the role of tail autotomy on escape behavior (e.g., Vitt and Cooper, 1986; Formanowicz et al.,

DISTRIBUTION AND HABITAT REQUIREMENTS OF THE WHITE-CLAWED CRAYFISH, AUSTROPOTAMOBIUS PALLIPES, IN A STREAM FROM THE PAYS DE LOIRE REGION, FRANCE: AN EXPERIMENTAL AND DESCRIPTIVE STUDY

A population of white-clawed crayfish (Austropotamobius pallipes) was studied from January to October 2000 in a stream from the Pays de Loire region (Western France). An experimental modification of habitat was performed in four stream sections by providing refuges for crayfish, followed by a regular survey of population dynamics in these areas. The crayfish distribution along the brook was studied in relation to several parameters, including water quality, current speed, brook depth and presence of refuges for crayfish. Presence of hiding places was the only habitat parameter correlated with crayfish distribution along the stream whereas colonization process in modified sections was determined by sun exposure and current speed conditions. Despite a presumably high growth rate and its ability to reach locally important densities, the population appeared to be fragmented.

Spatially heterogeneous refugia and predation risk in intertidal salt marshes

The effect of habitat structure on interactions between predators and prey may vary spatially. In estuarine salt marshes, heterogeneity in refuge quality derives from spatial variation in vegetation structure and in tidal inundation. We investigated whether predation by blue crabs on periwinkle snails was influenced by distance from the seaward edge of the salt marsh and by characteristics of the primary habitat structure, smooth cordgrass (Spartina alterniflora). Spartina may provide refuge for snails and interfere with foraging by crabs. Furthermore, predation risk should decline with distance from the seaward edge because landward regions require more travel time for crabs during tidal inundation. We investigated these processes using a comparative survey of snails and habitat traits, an experiment that assessed the crab population and measured predation risk, and a size‐structured model that estimated encounter rates. Taken together, these approaches indicated that predation risk for snails was lower where Spartina was present and was lower in a landward direction. Furthermore, Spartina architecture and distance from the seaward edge interacted. The strength of the predation gradient between seaward and landward regions of the marsh was greater where Spartina was tall or dense. These predation gradients emerge because vegetation and distance inland decrease encounter rates between crabs and snails. This study suggests that habitat modification, a process not uncommon in salt marshes, may have consequences for interactions among intertidal fauna.

Why are some weta (Orthoptera: Stenopelmatidae) vulnerable yet others are common?

The large (4 g) to very large (40 g) stenopelmatid orthopterans of New Zealand are known collectively as weta. A consideration of 20 species of Hemideina, Deinacrida and tusked weta reveals that at one end of a vulnerability gradient are those species which thrive in the presence of key predators (rats), while at the other end are species that have become extinct on the mainland but still survive on predator-free island refuges. Habitat modification does not appear to be a factor in these extinctions. This paper reviews the lifestyles and some important biotic parameters that seem to determine their relative vulnerability along this gradient. When predators are present, the factors leading to extinction are large body size, use of temporary refuges, protective quality of the refuges, time spent on the ground and the effectiveness of their defensive behaviour.

Settlement and early post-settlement survival of sessile marine invertebrates on topographically complex surfaces:the importance of refuge dimensions and adult morphology

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 137:161-171 (1996) - doi:10.3354/meps137161 Settlement and early post-settlement survival of sessile marine invertebrates on topographically complex surfaces: the importance of refuge dimensions and adult morphology Walters LJ, Wethey DS We predicted that both refuge dimension and growth form would influence settlement and short-term post-settlement success (&LT=7 d) of sessile marine invertebrates that live attached to hard substrata in low energy environments. Individuals with unlimited attachment to the substrata should rapidly be protected by their growth form, thus decreasing their need to settle in refuges and limiting the length of time any locations on heterogeneous substrata act as refuges. Alternatively, organisms with limited attachment to the substrata should remain susceptible to the causes of mortality for a longer time, and as a result should settle in high quality refuges (sites that protect individuals from competitors, predators or physical disturbance events until either a size refuge or reproductive maturity is obtained). Results agreed with these predictions for 4 species of invertebrates examined on both the topographically complex surface of the solitary ascidian Styela plicata (hereafter Styela) and on settlement plates with uniformly spaced roughness elements that mimicked the heights of roughness elements (2.0 and 5.0 mm) found on Styela in Beaufort, North Carolina, USA. On all surfaces, the 2 species with limited attachment to the substrata, Balanus sp. (aclonal, solitary) and Bugula neritina (clonal, arborescent), settled almost exclusively in the location that provided individuals with the best refuge: the crevices formed where the bases of roughness elements intersect with the flat surfaces. Additionally, when roughness elements of various heights were present (Styela,range: 0.6 to 8.8 mm), intermediate size roughness elements (2.0 &LT x &LT= 5.0 mm) were picked over 72% of the time. Settlement locations and locations where survival were enhanced were less consistent for the 2 species with unlimited attachment to the substrata: a clonal, encrusting form (Schizoporella errata) and a clonal stolon-mat form (Tubularia crocea). Fewer individuals of these 2 species settled on roughness elements on Styela and when they did, they were not restricted to the bases of the roughness elements. On the plate surfaces, most settlement did occur in crevices, but both species grew away from this location within days and short-term survival was not consistently greater in this location. Additional trials were run on plates with pits of the same maximum dimensions as the tested roughness elements (2.0 and 5.0 mm depth) to see if crevices and pits provide refuges of equal quality for newly settled individuals. Only survival of Balanus sp. recruits was greatest in both crevices and pits. Evidence for active choice of settlement location comes from consistent results in trials in which some larvae settled in greater numbers on specific size roughness elements on Styela and in areas of high erosion. Overall, these results show that one must be very cautious when generalizing about refuge quality on heterogeneous surfaces, and to determine if a location is a spatial refuge, it is critical to consider: (1) the dimensions of the larva, (2) the relative dimensions of the individual and potential refuge location at any point in time from the moment settlement occurred, and (3) the growth form of the individual which is related to its need for protection from biotic and abiotic sources of mortality. Larval ecology . Settlement . Refuges . Surface heterogeneity . Fouling community Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 137. Publication date: June 27, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

FACTORS REGULATING MICROHABITAT USE BY YOUNG JUVENILE SPINY LOBSTERS, PANULIRUS ARGUS: FOOD AND SHELTER

Habitation patterns ofalgal-dwellingjuvenile spiny lobsters, Panulirus argus, are apparently regulated by a) the availability of epifaunal prey, and/or b) limited sheltering qualities provided by algal branching. Predictions derived from each hypothesis were tested by monitoring emigration from normal (prey abundant), rinsed (prey reduced), and rinsed but structurally enhanced clumps of red algae, Laurencia spp. Density dependent emigration from untreated clumps containing natural prey, and markedly increased emigration from clumps nearly void of potential prey, suggest that trophic pressures play an important role in regulating algal habitation. Solitary dwelling induced by agonistic behavior may function to reduce required foraging area, thus minimizing both exposure to predators and energetic expenditures. The young benthic stages of the spiny lobster Panulirus argus inhabit intricately branched clumps of red algae, Laurencia spp., in shallow habitats of Florida Bay and the Florida Keys (Marx and Herrnkind, in press). Small size, cryptic behavior, camouflaged pigmentation, and disruptive markings (light-dark banding of appendages and dorsal stripe), seemingly adapt the early stages to residency within algal clumps. Moreover, algae provide abundant prey in the form of diverse epifaunal invertebrates including small gastropod mollusks, isopods, amphipods, and ostracods, all of which are commonly found in the gut contents of young lobsters (Marx and Herrnkind, in press). Young benthic stages are typically solitary in small algal clumps, or occupy widely spaced portions of large clumps, and exhibit aggressively maintained isolation in aquaria. Solitary dwelling behaviorally distinguishes postsettlement stages from older juveniles which are gregarious (Kanciruk, 1980). These collective observations suggest that macroalgal habitation functions to protect the otherwise susceptible young stages from predators and physical stresses while simultaneously providing access to food, thus enhancing the value of algae as a refugium. We examined this relationship by experimentally testing the effects of food and physical sheltering factors on residency patterns of young benthic stages within algal clumps. Assuming trophic regulation, we reasoned that a young lobster should remain within a clump so long as sufficient food is available, but emigrate when prey abundance is low. Increased food searching when prey is scarce conceivably exacerbates agonism by causing frequent contact between residents, or food scarcity might induce increased individual aggressiveness. One predicts increased emigration as a result in either case. Assuming that refuge quality is a regulating factor, we propose that macroalgal clumps are selected as habitat because of physical features independent of prey availability. Alternatively, early benthic stages may occupy algae only in the absence of rock crevices, which constitute the typical shelter for slightly older juveniles in other habitats (Andree, 1981). Below, we report on experimental tests of each prediction and discuss the implications with respect to the behavioral ecology and population dynamics of young juvenile lobsters. Specifying the nature of the biological relationship between spiny lobsters and their settlement habitat is essential to management of the multimillion dollar spiny lobster fishery and will contribute to our understanding of life history tactics.