Effects Of Habitat Quality Research Articles

Habitat Effects on Physiological Stress Response in Nestling Blue Tits Are Mediated through Parasitism

Abstract We investigated determinants of the physiological stress response mediated by stress proteins in blue tit Cyanistes caeruleus nestlings growing up in oak forests in central Spain, resulting from different forest management practices. We assessed circulating levels of the heat-shock protein HSP60 as an integrated physiological measure of the conditions experienced by nestlings during postnatal development. The effects of habitat quality and parasite infections on nestling rearing environment were then assessed through this measurement of stress response. Our results showed that newly acquired ecto- and hemoparasite infections were associated with forest habitat structural characteristics, higher prevalence of fleas and blood parasites in more mature forests, and higher prevalence of blowflies in degraded forests. While habitat characteristics did not explain variation in stress protein levels, infestation by blowfly larvae of the genus Protocalliphora and hematozoa infection by Leucocytozoon were significantly associated with higher levels of HSP60. Thus, upregulation of the expression of certain stress proteins seems to be a common physiological mechanism to alleviate the negative impact of parasite infections in growing birds. Habitat characteristics may thus indirectly determine growth conditions for forest birds mediated through their association with one of the most important selection pressures for offspring development, parasite infections.

Spatial movements of grey partridge Perdix perdix: male-biased spring dispersal and effect of habitat quality

The Grey Partridge Perdix perdix is a sedentary species with a surplus of males in spring populations. It experienced a dramatic decline in Europe primarily due to habitat loss that may have forced the species to modify its dispersal behaviour, a less transparent source of populations threats. We analysed the dispersal patterns of Grey Partridges during pre- and post-breeding periods in two landscapes with different habitat quality in the Czech Republic. Grey Partridges tended to pair off quickly, with most pre-breeding movements executed in pairs. The birds usually dispersed over a few hundred metres indicating that the habitat conditions in a landscape with a carrying capacity of 2–5 pairs/1 km2 was not below the threshold initiating strong dispersal, as observed in extreme habitats and at the northern limits of the species´ distribution range. A few single males that had remained unpaired until April also finally bred. However, the high level of sedentariness of males in a good landscape suggested that males prefer to stay near wintering sites unless habitat sources become limited. Unlike the males, the females dispersed in a wide range of distances with an extensive overlap in both landscapes. Autumn movements did not differ between the sexes, but were longer than the pre-breeding movements and increased in a poor landscape. We conclude that both reduced habitat availability and reduced mating opportunities initialise primarily male-biased breeding dispersal in Grey Partridge populations.

Effects of habitat quality and fishing on Caribbean spotted spiny lobster populations

Summary Overfishing has had detrimental impacts on many marine populations. However, measurements of the effect of exploitation are often confounded by intersite differences in habitat quality. To assess the effects of fishing and habitat quality on spotted spiny lobster Panulirus guttatus, the target of a luxury fishery in the Caribbean, lobster populations were assessed on 12 reefs around Anguilla, British West Indies. Habitat quality was measured by the availability of foraging habitat. Fishing intensity was estimated through interviews with fishers. Spotted spiny lobster densities were significantly higher on reefs with good‐quality habitat than on poorer‐quality reefs. However, mean lobster size remained constant regardless of habitat quality. In contrast, lobsters were on average smaller in heavily fished than in unfished areas because of the removal of the largest size classes by fishers. Changes in densities as a result of fishing could not be detected, and there was no interaction between fishing pressure and habitat quality. The lack of an observable effect of fishing on lobster population densities may be because fishers more intensively target high‐quality habitats. Fishing has probably reduced lobster densities on high‐quality reefs to a greater extent than on low‐quality reefs, but the high productivity of good‐quality sites is still sustaining more intense fishing. Synthesis and applications. The importance of habitat quality in sustaining P. guttatus populations in the face of intense exploitation suggests that management efforts should be aimed at enhancing reef health. The latter may be achieved through the establishment of no‐take areas on good‐quality reefs. Such actions should, however, be expected to generate conflicts with stakeholders because these reefs are currently those most heavily exploited.

Population stage structure, survival and recruitment in the endangered East African forest herb Saintpaulia

Climatic seasonality, local habitat quality, and edge effects created by forest fragmentation due to human activity may affect the performance of endangered rain forest understory herbs. Viability and seasonal dynamics of the populations of the endangered Saintpaulia confusa, S. difficilis, and S. grotei were studied in a protected seasonal submontane forest in NE Tanzania by examining plant life-history traits, population stage structure, and the effects of habitat quality on plant performance. The population stage structures were of the dynamic type. There was a lower frequency of seedlings (57.9%) and higher frequency of juvenile (13.3%) and adult plants (28.8%) in S. confusa than in S. difficilis (74%, 10.7% and 15.3%, respectively). Seedling recruitment occurred from May to August with an average of 54, 103 and 38 emerged seedlings per 1 m2 study plot (S. confusa, S. difficilis, and S. grotei, respectively). Presence of the seed bank was also an indication of the regeneration potential of the populations. Mortality was high during the dry and hot season from December to March. Survival was lowest in juvenile plants, higher in sterile adult plants and the highest in fertile adult plants. Because survival was the lowest on dry substrates under open canopy, our data suggest that forest fragmentation, by reducing shade and humidity, will increase mortality in Saintpaulia. Furthermore, since the mortality was highest in seedlings and juveniles, forest fragmentation is likely to impede the regeneration of the Saintpaulia populations.

The effect of habitat quality on foraging patterns, provisioning rate and nestling growth in Corsican Blue Tits Parus caeruleus

Many bird species face seasonal and spatial variation in the availability of the specific food required to rear chicks. Caterpillar availability is often identified as the most important factor determining chick quality and breeding success in forest birds, such as tits Parus spp. It is assumed that parents play an important role in mediating the effect of environment on chick development. A reduction in prey availability should therefore result in increased foraging effort to maintain the amount of food required for optimal chick development. To investigate the capacity of adults to compensate for a reduction in food supply, we compared the foraging behaviour of Blue Tits Parus caeruleus breeding in rich and poor habitats in Corsica. We monitored the foraging effort of adults using radiotelemetry. We also identified and quantified prey items provided to nestlings by using a video camera mounted on the nest. We found that the mean travelling distance of adults was twice as great in the poor habitat as it was in the rich. Despite the marked difference in foraging distance, the proportion of optimal prey (caterpillars) in the diet of the chicks and the total biomass per hour per chick did not differ between the two habitats. We argue that relationships between habitat richness, offspring quality and breeding success cannot be understood adequately without quantifying parental effort.

The effects of habitat quality and female size on the productivity of the lesser spotted eagle Aquila pomarina in the light of the alternative prey hypothesis

Habitat quality is an important but insufficiently understood concept in ecology and conservation biology, due to geographic and temporal variation as well as interaction with individual quality. In 1994–2002, we studied the Estonian population of the lesser spotted eagle Aquila pomarina in order to (1) explore the relative contributions of habitat and female size in reproductive success; (2) check for a switch to alternative prey in vole‐poor years and the relevant variation in annual habitat quality as confirmed in the common buzzard Buteo buteo in the same area. We measured five landscape variables, the number of neighbouring conspecifics and the relative size of the female according to large moulted feathers in 77 nesting territories, and related this to the eagles’ productivity in vole‐rich and vole‐poor years. Nesting lesser spotted eagles benefited from heterogeneous landscapes and suffered from the neighbourhood of conspecifics. There was no evidence that different‐sized females used different habitats. In general, female size was positively related to productivity in vole‐poor but not vole‐rich years, but in the presence of competitors, large size appeared to be disadvantageous. The mean annual productivity of the eagle was well correlated with that of the buzzard, both having peaks after every three years. In contrast to the buzzard, the share of voles in the eagle's diet and its habitat quality did not differ significantly between good and poor years. We concluded that despite a superficial ecological similarity to the buzzard, the lesser spotted eagle did not behave as predicted by the alternative prey hypothesis, but the study confirmed that annual variation in prey utilization and relative habitat quality are parts of the same functional response. Non‐switching to alternative prey may be related to a historical foraging strategy, used by the eagles before they spread to agricultural landscapes, since the current effects of body size strongly suggested food shortage in vole‐poor years.

Demographic Variation Among Udzungwa Red Colobus in Relation to Gross Ecological and Sociological Parameters

We evaluated variation in group size and composition of Udzungwa red colobus (Procolobus gordonorum) in relation to gross-habitat and sociological parameters. The endangered species is endemic to the Udzungwa Mountains and nearby forests in the Kilombero Valley of south-central Tanzania. We counted 63 groups in 10 forests, ranging in altitude from 250 to 1,800 m. Group size ranged from 7 to 83 (x = 36.3) individuals and adult sex ratios (females/male) ranged from 1.5 to 7.3 (x = 3.5), excluding solitary individuals. Group size was influenced by several habitat parameters, including tree density, degree of deciduousness, and forest size. Groups were largest in large blocks of mature, moist, mixed evergreen and semideciduous forests, but group size is not correlated with altitude. Groups in a highly degraded forest appeared to have fission-fusion societies. The effect of habitat quality on age-sex composition of groups was most apparent in natality and less so in survivorship of adult females and juveniles. The number of adult males in groups accounted for 50% of the variance in group size and 34–39% of the variance in numbers of adult females in groups. Habitat quality affects natality more than demographic parameters do. Groups with a low proportion of adult females had greater juvenile survivorship, perhaps because of lower food competition between these two classes. We proffer hypotheses based on our study and previous intertaxonal comparisons to explain cause and effect relationships between habitat quality and demography. Finally, our study demonstrates the importance of large blocks of old-growth forest to the conservation of Udzungwa red colobus, and we make recommendations for conservation and research.

An extensive study of the foraging ecology of beavers (Castor canadensis) in relation to habitat quality

The objective of this study was to examine the foraging behaviour of the beaver (Castor canadensis Kuhl, 1820) and to explain its selection of terrestrial woody plant species according to central place foraging theory. Limitations in variety of food items in most studies with regard to size and (or) distance from the central place and information on availability of forage choices give a partial view of the subject. In this study, the theory is tested in a natural environment with high variability in food items with regard to these factors. Foraging choices by beavers were inspected by measuring variables on cut and uncut trees of every species encountered within 1 m of trail systems made by 25 beaver colonies in Kouchibouguac National Park in New Brunswick, Canada, thereby quantifying the availability of the different food items. The effect of habitat quality (food availability) on the foraging behaviour of beavers was also tested. The results of this study suggest that with increasing distance from the pond, beavers in high-quality habitats selected fewer, but larger, trees and are more species selective. This selectivity was diminished in habitats of lower quality. The results of this study are consistent with the predictions of the central foraging theory.

Comparing the freezing susceptibility of third-instar larvae of Gnorimus variabilis (Cetoniidae: Trichiinae) from three distant geographical regions

We compared the freezing susceptibility of three populations of Gnorimus variabilis (L., 1758) (Coleoptera: Cetoniidae) sampled from three distant locations in France. To separate the effects of habitat quality from those of genetics, we reared imagos from all field populations in a common garden experiment until the emergence of the third-instar larvae. The local climate appeared to determine the cold hardiness of the third-instar larvae, which live exclusively in cold seasons. The geographical location had an effect on the frost resistance (supercooling point) of the third-instar larvae of G. variabilis. We found no significant differences between the supercooling points of the populations originating from separate latitudes but from the same longitude, Sare (–10.9 ± 4.1 °C) and Husson (–11.5 ± 3.8 °C). Nonetheless, significant differences occurred between the larvae originating from the same northern latitude but from separate longitudes, Husson and La Robertsau (–17.8 ± 2.9 °C). It is the first time that a highly significant difference in the supercooling point of one stage within a single species has been observed along geographical gradients. Moreover, 19 of the 24 larvae originating from La Robertsau were alive after they were kept for 22 h at –10 °C compared with only 7 of the 24 larvae originating from Sare. When the three populations were reared in the laboratory under the same experimental conditions, the differential cryoresistance was preserved. It is likely that the greater freezing resistance found in the third-instar larvae of G. variabilis from La Robertsau could have a genetic component.

Latitudinal patterns in abundance and life‐history traits of the mole crabEmerita brasiliensison South American sandy beaches

ABSTRACTDemographic and life‐history attributes of the mole crabEmerita brasiliensiswere analysed along 2700 km of the Atlantic coast of South America, including sandy beaches at the southernmost limit (Uruguay) and at the core of its geographical range (Brazil). Population features varied markedly within this range and exhibited systematic geographical patterns of variation. Abundance significantly increased from temperate to subtropical beaches, and the same held true for the asymptotic weight of males. Conversely, length at maturity and asymptotic weight of females increased from subtropical to temperate beaches, being inversely related to sea water temperature. Macroecological patterns in abundance and body weight showed the first large‐scale evidence of scaling of population density to body size for a sandy beach population. Mortality rates (both sexes) followed a nonlinear increase from low‐density temperate beaches to high‐density subtropical beaches. The effect of habitat quality and availability could explain discontinuities in the species distribution within its range, and also differential responses in life‐history attributes at a local scale. Asymmetries and converse latitudinal trends between sexes suggest that there is not a single general factor determining large‐scale patterns in life‐history traits of this species. Our results reinforce the view that density‐dependent and environmental factors operating together regulate sandy beach populations. The need to develop macroecological studies in sandy beach ecology is highlighted, as knowledge acquired from local to large spatial scales throws light on population structure and regulation mechanisms.

Population density and small-scale variation in habitat quality affect phenotypic quality in roe deer

We tested for fine-scale spatial heterogeneity in habitat quality in a roe deer (Capreolus capreolus) population in the Chizé reserve located in western France by measuring spatial variation in the availability and plant nitrogen content of principal and preferred plant species. There were significant differences in habitat quality within the reserve: the principal food plants in spring and summer occurred more frequently in the oak woodland in the north than in the beech woodland in the south of the reserve. Within species, plants in the north had higher nitrogen contents than in the south. There was a positive spatial covariation between habitat quality, local density and fawn body weight: animal densities and fawn body weights were highest in the north, the best habitat (i.e. the habitat with more abundant food of higher quality). These results differ from those recently obtained on red deer (Cervus elaphus). We suggest that spatial organization and foraging behaviour must be accounted for when considering the effect of habitat quality on individual fitness of ungulates.

Metapopulation Dynamics: Effects of Habitat Quality and Landscape Structure

Metapopulation Dynamics: Effects of Habitat Quality and Landscape Structure

METAPOPULATION DYNAMICS: EFFECTS OF HABITAT QUALITY AND LANDSCAPE STRUCTURE

Metapopulation dynamics have received much attention in conservation and population biology, but the standard approach has also been criticized for being too restrictive, as it is based on the effects of habitat patch area and isolation only. Here we demonstrate how the effects of habitat quality (extra environmental factors) and detailed landscape structure (described with GIS [Geographical Information System]) can be included in a spatially realistic metapopulation model, the incidence function model. Expanded models are tested with a large data set on the Glanville fritillary butterfly (Melitaea cinxia). The incidence function model supplemented with additional environmental factors revealed some new and confirmed some previously known interactions between M. cinxia and its environment. However, the ability of the additional environmental factors to explain the error in the fit of the basic model was generally low (≤15%). In the second variant of the basic model, landscape structure was used to modify effective patch isolations. This approach, though biologically appealing, failed to improve significantly the fit of the incidence function model. There are several possible reasons for this failure, including inaccurate satellite data, problems with habitat classification, and most importantly, generic problems in the modeling of migration. Our results demonstrate that additional complexity beyond the effects of habitat patch area and isolation does not necessarily improve the predictive power of a metapopulation model.

Evaluating the Effects of Habitat Quality, Connectivity, and Catastrophes on a Threatened Species

Evaluating the Effects of Habitat Quality, Connectivity, and Catastrophes on a Threatened Species

Alternative reproductive tactics in atlantic salmon: factors affecting mature parr success

In Atlantic salmon, as in most salmonids, males can mature early in the life cycle, as small freshwater fish, termed parr, and/or undergo a sea migration before maturing as full–size adults. The alternative life histories are contingent on environmental and social circumstances, such as growth rate, territory quality or any other factor that affects the individual9s state. In order to model the choice of life history in this group of commercially valuable species, it is necessary to understand not only the relative contribution of the different male types to subsequent generations, but also to know the factors that affect reproductive success in each type. In this paper we present the results of a study designed to investigate the factors that affect the reproductive success of mature parr. We used highly polymorphic minisatellite DNA markers to analyse paternity in a series of mating experiments where the number and body size of parr were manipulated. The fraction of eggs fertilized by mature parr ranged from 26 to 40 per cent, with individual parr fertilizing up to 26 per cent of the eggs. A strong positive correlation was found between parr size and reproductive success. The relative success of parr decreased with increasing parr number. Data from this and other studies on variation in the timing and degree of parr reproductive success are discussed in relation to the evolution of male mating strategies and life history in salmonids.

Effects of Habitat Quality and Hunting Pressure on Arboreal Folivore Densities in Neotropical Forests: A Case Study of Howler Monkeys (Alouatta spp.)

This large-scale geographic comparison examines the effects of subsistence hunting pressure and several indirect indicators of habitat quality on the abundance of howler monkeys {Alouatta spp.), the best studied and the most folivorous of all platyrrhine primates. Alouatta population densities were obtained from a standardized series of line-transect censuses undertaken at 23 Amazonian forest sites (1987–1995), including annually flooded (várzea), unflooded (terra firme), and eastern Amazonian transitional terra firme forests. A total of 83 density estimates from elsewhere were compiled from a comprehensive review of field studies from southern Mexico to northern Argentina. Howler density and biomass in Neotropical forests is profoundly affected by degree of hunting pressure, structural heterogeneity of the forest canopy, and to a lesser extent, the rainfall seasonality, total rainfall, and latitude of a given site. Mild gradients of forest elevation were a poor predictor of howler densities. In evergreen forests of lowland Amazonia, distance to major white-water rivers, which covaries with forest heterogeneity and soil fertility, is the best single predictor of howler densities. In Amazonia, habitat-specific patterns of distribution and abundance of Alouatta and other arboreal folivores conform to geochemical gradients determined by watershed types and their consequences for soil fertility. Results presented here confirm suggestions for Old World generalist herbivores that howler monkeys face strong dietary constraints which are most likely related to quality, phenology and productivity of digestible foliage during periods of resource scarcity.

Helper Effects on Variance Components of Fitness in the Cooperatively Breeding Red-Cockaded Woodpecker

Studies of how avian helpers influence reproduction have concentrated on mean effects. We examined the effects helpers have on variance in reproductive success and breeder survival in the Red-cockaded Woodpecker (Picoides borealis). Variance in reproduction and survival are components of fitness, and increased variance results in decreased fitness. We found that helpers did not affect variance in breeder survival, but variance in reproductive success was affected by helpers at nests that produced young. When we exclude groups in which breeding failed or was not attempted, reproductive success is more variable among groups with one helper than among groups with no helpers or groups with two helpers, regardless of the age of the female breeder. A survey of the literature showed no clear pattern in other cooperative breeders, although the presence of helpers often was associated with higher variances. Like helper effects on mean reproductive success, helper effects on variance in reproductive success might be confounded by effects of habitat quality. Received 24 April 1995, accepted 6 September 1995.

Army ant population dynamics: the effects of habitat quality and reserve size on population size and time to extinction

A simple deterministic model is used to examine the effects of habitat size and quality upon the sizes and chances of extinction of isolated populations of a species of neotropical army ant, Eciton burchelli . The results of the model suggest that equilibrium population size is influenced more by habitat size than quality. Similarly, expected extinction times increase exponentially with habitat size but depend on quality only through its minor effects upon the equilibrium population size. Such effects may be crucial from a conservation point of view, however, because of the strong dependence of extinction probabilities on equilibrium population size. Density-independent effects in the form of queen senescence also have strong effects on expected extinction times but not on equilibrium population size. The results are used to predict which of several islands and peninsulas in and around Gatun Lake, Panama, have a high probability of still being populated by E. burchelli after their isolation from the surrounding tropical rain forest.

Statistical inference on patch-specific survival and movement rates from marked animals

Empirical estimates of patch-specific survival and movement rates are needed to parametrize spatially explicit population models, and for inference on the effects of habitat quality and fragmentation on populations. Data from radio-marked animals, in which both the fates and habitat locations of animals are known over time, can be used in conjunction with continuous-time proportional hazards models to obtain inferences on survival rates. Discrete-time conditional logistic models may provide inference on both survival and movement rates. We use Monte Carlo simulation to investigate accuracy of estimates of survival from both approaches, and movement rates from conditional logistic regression, for two habitats. Bias was low (relative bias < 0.04) and interval coverage accurate (close to the nominal 0.95) for estimates of habitat effect on survival based on proportional hazards. Bias was high ( $$\bar x$$ relative bias 0.60) and interval coverage poor ( $$\bar x$$ = 0.26 vs. nominal 0.95) for estimates of habitat effect based on conditional logistic regression; bias was especially influenced by heterogeneity in survival and the shape of the hazard function, whereas both bias and coverage were affected by ‘memory’ effects in movement patterns. Bias estimates of movement rate was low ( $$\bar x$$ relative bias < 0.05), but interval coverage was poor ( $$\bar x$$ = 0.48–0.80), possibly as a result of poor performance of a Taylor series estimate of variance. An example is provided from a radio-telemetry study of 47 wintering American woodcock (Scolopax minor), illustrating practical difficulties in field studies to parametrize these models. We also discuss extensions of continuous-time models to explicitly include a movement process, and further examine tradeoffs between continuous and discrete models.

The effect of habitat quality on breeding performance in the red-backed shrike ( Lanius collurio)

The effect of habitat quality on breeding performance in the red-backed shrike ( Lanius collurio)