Interspecific competition: A mechanism for rodent succession after fire in wet heathland

Abstract A competitive interaction between two species of sympatric native rodents was demonstrated experimentally in Myall Lakes National Park (NSW, Australia). The previously documented replacement of Pseudomys gracilicaudatus by Rattus lutreolus in areas of wet heath in this region implied that competition may be the mechanism facilitating this succession. We present experimental evidence to support this suggestion. Removal of the larger R. lutreolus caused a significant increase in abundance of P. gracilicaudatus on five experimental sites in comparison to five unmanipulated control sites. The sites used in this experiment were chosen from three ages of wet heath regenerating after fire. These three ages represent key stages in the replacement of P. gracilicaudatus by R. lutreolus and the occurrence of competition in each of these ages indicates that competition plays an important role in this succession. In the initial stages of the experiment when R. lutreolus were removed they were replaced by new R. lutreolus individuals. This has been interpreted as evidence of strong intraspecific competition. After removal of R. lutreolus, P. gracilicaudatus expanded its habitat range into microhabitats that had formerly been occupied by R. lutreolus and reduced its range in microhabitats previously occupied by P. gracilicaudatus. This leads us to believe that P. gracilicaudatus was occupying inferior microhabitat before the removal of R. lutreolus, which had excluded it from more preferable microhabitat.     

Habitat utilization patterns of sympatric populations of Pseudomys gracilicaudatus and Rattus lutreolus in coastal heathland: A multivariate analysis

Abstract Habitat usage characteristics of two species of native murid rodents, Pseudomys gracilicaudatus and Rattus lutreolus were investigated on an area of coastal heathland at Myall Lakes National Park. A grid of 151 trap stations comprising 17 traplines was positioned across a mosaic of habitats. At each trap station 19 structural vegetation and physical variables known to affect the microdistribution of small mammals were measured. Multivariate statistical procedures identified those microhabitat variables that contribute to individual species' habitat use and habitat partitioning, and reduce potential competition for space. Cluster analysis classified trap stations into one of six habitat types that were mapped on the study area, identifying a heterogeneous assemblage of interlocking habitats. The pattern is a consequence of topographic variation on the site and, to a lesser extent, its fire history. Trapping results show P. gracilicaudatus and R. lutreolus exhibit similar macrohabitat selection, preferring topographically low habitats, with both species predominantly occupying short dense heath with dense sedge cover. The high overlap in macrohabitat use is greatly reduced when considered trap station by trap station, so that discriminant function and multiple regression analyses demonstrate marked microhabitat selection. Elevation was a highly significant variable, accounting for 41% and 27% of the variance in the habitat used by P. gracilicaudatus and R. lutreolus, respectively. This variable represents a soil moisture gradient that determines changes in the floristic and structural components of the biotic environment. Two other structural vegetation variables and vegetation height contributed 30% of the variance in P. gracilicaudatus distribution. Sedge cover was found to be significant and explained 13% of the variance in R. lutreolus distribution. Within-habitat separation was explained best with a linear combination of variables in a discriminant function, rather than by any single variable. Differential microhabitat selection, interference competition and diet separation appear to be the major factors facilitating coexistence of these two species.     

Responses of two species of heathland rodents to habitat manipulation: Vegetation density thresholds and the habitat accommodation model

The abundance of two native rodent species, Rattus lutreolus and Pseudomys gracilicaudatus, has been shown to correlate with vegetation density in coastal wet heath. Fox's habitat accommodation model relates relative abundances of such small mammal species to heathland vegetation regeneration following disturbance. Implicit in the model is recognition that it is successional changes in vegetation, not time per se, that drives the responses of small mammal species along a regeneration axis. Using a brush‐cutter we deliberately removed approximately 85% of vegetation around trapping stations and recorded significant reductions in the abundance of both P. gracilicaudatus (an earlier‐stage colonizing species) and R. lutreolus (a late seral‐stage species). A significant decrease in the abundance of only the latter had been demonstrated previously when 60–70% of the vegetation had been removed. Following the brush‐cutting both species re‐entered the mammalian secondary succession at different times, first P. gracilicaudatus followed by R. lutreolus after the vegetation cover thresholds of each species had been reached. The impact of this habitat manipulation experiment was to produce a retrogression of the small mammal succession, experimentally demonstrating causality between changes in vegetation density and subsequent small mammal habitat use.     

Recolonization of coastal heath by Pseudomys novaehollandiae (Muridae) following sand mining

The regeneration of coastal heath after disturbance by mineral sand mining was studied on mid-seral stages from 4 to 11 years old at Hawks Nest, N.S.W. The main purpose was to gain some understanding of factors influencing recolonization by pioneer species of small mammals such as Pseudomys novaehollandiae. Changes in floristics and vegetation structure with time were studied as possible contributing factors together with environmental variables. An apparently linear relationship was found between plant species diversity (X₁) and P. novaehollandiae biomass which was also correlated with an index representing the proportion of heath species present (X₂). Both plant species diversity and P. novaehollandiae biomass showed a linear increase with regeneration age. A multiple regression analysis revealed a predictive equation explaining 96% of the variation in P. novaehollandiae biomass (Y): Y=-7.92 + 1.21X₁+3.92X₂ - 3.09X₃ The third variable (X₃) is a measure of soil hardness. A path diagram using contribution coefficients based on a partial correlation analysis included the effects of vegetation structure below 50 cm and regeneration age. On mid-seral stages after sand mining P. novaehollandiae is associated with areas having a variety of heath plants, with vegetation cover below 50 cm and softer substrates; its abundance increases with increasing regeneration age and with the total amount of vegetation present. A minimum of 20 years is seen to be necessary for both total amount of vegetation and P. novaehollandiae biomass to reach values encountered on control plots of undisturbed heath.     

Habitat preferences of small mammals in tropical open-forest of the Northern Territory

Pattern analysis was used to investigate the habitat preferences of five small mammal species in tropical open-forest of the Northern Territory. Fifty-one sites were classified by faunal abundance and the groups examined for significant differences in vegetation structural attributes and plant species in both dry and wet seasons. The omnivore Isoodon macrourus showed strong association with floristic and vegetation structural attributes only in the dry season, when areas with a dense understorey of small trees and shrubs and a high percentage of leaf litter cover were favoured. Of the two primarily carnivorous species, Antechinus bellus was related strongly with floristic and structural attributes in both seasons and showed a consistent preference for areas with relatively dense low-level foliage (< 2m). By contrast, Dasyurus hallucatus was associated more with the structurally simple open-forest types. Of the two mainly herbivorous species Mesembdomys gouldii showed associations only withfioristics in both seasons, while the habitat relationships of Trichosurus arnhemensis were very weak due to its low abundance in the study area. The number and strength of animal/habitat relationships were greatest in the dry season. Forest types with dense mid-level foliage and abundant hollow logs and leaf litter had the greatest mammal richness and abundance; these areas may be critical to the survival of local mammal populations. A comparison of site-groups, defined independently on the basis of fauna, floristics or structure, showed that animal groups overlapped one to six of the habitat groups. The animal's perception of s‘habitat’ may thus differ from that of humans, or that defined by measurement of habitat attributes.     

Relationships between native small mammals and native and introduced large herbivores

Australia has a range of native and introduced large herbivores that could affect the abundance of small mammals through direct and indirect effects. Here we study the relationship between occurrence of the introduced rusa deer (Rusa timorensis) and the native swamp wallaby (Wallabia bicolor), and the abundance of four species of native small mammals in coastal heath vegetation with varying fire history. The abundance of two species, the brown antechinus (Antechinus stuartii) and bush rat (Rattus fuscipes), was related to occurrence of large herbivores and was dependent also on fire history. Abundance of swamp rats (R. lutreolus) and New Holland mice (Pseudomys novaehollandiae) was not related to the occurrence of any of the large herbivores, and did not depend on fire history. At sites burned within the last 9 years, captures of brown antechinus were negatively related to both deer and wallaby occurrence, and captures of bush rats were negatively related to deer occurrence. However, at sites that burned more than 15 years ago, captures of brown antechinus and bush rats were not related to large herbivore occurrence. Overall there was either no relationship, or a negative one, between small mammals and the large herbivores. This mensurative study has demonstrated relationships between deer and wallabies and small mammals, with fire as an additional important factor. From the results of the current study we put forward a series of hypotheses that need to be tested by future experiments.     

A review of habitat selection by the swamp rat,Rattus lutreolus (Rodentia: Muridae)

Abstract This review clarifies important points on habitat selection by the Swamp Rat Rattus lutreolus (Rodentia: Muridae), a species that has been the subject of much research in Australia and has provided a useful model for understanding ecological and biological processes. It also provides an opportunity to cite important earlier research, not readily available through electronic search engines, thus bringing it into current literature to avoid its disappearance into Internet obscurity. We comment on some papers in the literature to correct errors detected and to emphasize the importance of due care in all aspects of a research project, including its reporting. We show that both floristic and structural components have been reported as important to an understanding of habitat and microhabitat selection by R. lutreolus and conclude that it is vegetation density that is of paramount importance. Female R. lutreolus are clearly dominant in driving microhabitat selection, occupying the ‘best’ or densest habitats with male R. lutreolus occupying the next best and Pseudomys or other species, where present occupying the remainder. This demonstrates the important role that intraspecific and interspecific competition play in determining habitat selection. Direct predation and the perception of predation risk may also play a role in habitat selection, again perceived to be pushing individuals towards denser vegetation, representing ‘better cover’. Whether these effects operate as bottom‐up or top‐down needs careful consideration. Climatic variables, such as ENSO‐affecting productivity, and related variables such as temperature and humidity may also play important roles in habitat selection, as can disturbance effects such as wildfire. The relative importance of all of these potential determining factors may vary from place to place, particularly when climatic clines are involved.     

Small mammal succession is determined by vegetation density rather than time elapsed since disturbance

Abstract We examined post‐fire responses of two sympatric Australian rodents, Pseudomys gracilicaudatus and Rattus lutreolus, as coastal wet heath regenerated following two high intensity wildfires. Pseudomys gracilicaudatus, an early serai‐stage species, recolonized an area burnt in August 1974 after one year, but took only 3 months to recolonize another area following a wildfire in October 1994. Rattus lutreolus, a late serai‐stage specialist, took approximately 3.6 years to recolonize following wildfire in August 1974, but had recolonized after only 4 months following wildfire in October 1994. We suggest that this apparent anomaly is associated with the rate of recovery of vegetation density. When the relative abundance of each species was plotted as a function of vegetation density, the trajectories following the two wildfires were concordant. An implicit relationship exists between time since wildfire and vegetation density. We make this relationship explicit by quantifying cover requirements for each species, and show that it is the resource continuum borne of regenerating vegetation (rather than time per se) that is important in determining the timing of small mammal successional sequences.     

Resource partitioning by small mammals in lowland heath communities of south-eastern Australia

Habitat selection by seven species of small mammals was investigated in three areas of heathland in Victoria. A total of 12 120 trapnights over 22 months was used to assess preference for different vegetation groups formed by clustering trap sites on (a) floristic and (b) structural criteria. Rattus lutreolus proved to have both floristic and structural requirements. Seasonal changes in distribution in relation to rainfall appeared to be dependent on soil type. Greatest movement occurred on sandy podzol soils. Pseudomys shortridgei selected the most diverse vegetation types. Rattus fuscipes preferred wet, structurally complex vegetation. Mus musculus appeared to fill the niche of Antechinus minimus and partially replace A. stuartii and A. flavipes when Antechinus spp. were absent. M. musculus seems to commonly fill three niches in these heathlands: fossorial insectivore, scansorial insectivore and immediate post-fire omnivore. A small mammal community structure of five major food niches may be common to both heathland and forest communities of south-eastern Australia.     

Chromosome evolution in Australian rodents

A total of 219 wild caught specimens representing 12 of the currently recognised 13 species and subspecies of Australian Rattus have been karyotyped. No two species possessed karyotypes in common, most species and several subspecies differing markedly in chromosome number. While the diploid number varied from 2n=32 to 2n=50, the fundamental number (FN) varied only from 60 to 62, suggesting that Robertsonian rearrangements have played a major role in karyotypic evolution in the group. — Karyotypically the Australian species of Rattus fall into two groups. — the R. lutreolus group and the R. sordidus group. Of the karyotypic forms encountered in the former group, that of R. lutreolus is probably most ancestral because it is identical to that of many Asian species of Rattus. Other karyotypic forms in the R. lutreolus group can be derived as follows: That of (1) R. tunneyi tunneyi and R. t. culmorum by a single fixed pericentric inversion; (2) R. fuscipes fuscipes, R. f. greyi, R. f. assimilis and R. f. coracius by two fixed fusions; (3) R. leucopus cooktownensis by three fixed fusions; and (4) R. leucopus leucopus by four fixed fusions. Of the R. sordidus group, R. s. villosissimus may possess the most ancestral karyotype with 2n=50 (FN=60), from which R. s. colletti (2n=42; FN=60) is derived by four fusions and R. s. sordidus (2n=32; FN=60) by nine fusions, four of which appear to be homologous with those R. s. colletti. — The karyotypic data are in accord with Taylor and Horner's (1973) suggestions that (1) R. t. tunneyi and R. t. culmorum belong to one species; (2) R. lut. lutreolus and R. lut. velutinus belong to one species; (3) R. leu. leucopus and R. leu. cooktownensis belong to one species and (4) R. f. fuscipes, R. f. greyi, R. f. assimilis and R. f. coracius belong to one species. However, the large karyotypic difference between R. s. sordidus and R. s. colletti and R. s. villosissimus may indicate that these groups belong to different biological species. — Supernumerary or B-chromosomes were found in R. f. assimilis and R. t. tunneyi. A single R. t. culmorum was heterozygous for a centric fusion.     

Competitive effects of Rattus lutreolus presence on food resource use by Pseudomys gracilicaudatus

Abstract We examined faecal samples of the eastern chestnut mouse (Pseudomys gracilicaudatus) that were collected during a removal experiment conducted in a coastal heathland at Myall Lakes National Park to see whether removal of the swamp rat (Rattus lutreolus) had any effects on food resource use by P. gracilicaudatus. The results showed that, at the young successional stage of vegetation (1. 5 years since last fire), the diet of P. gracilicaudatus changed significantly after the number of R. lutreolus was significantly reduced on the experimental sites. Two months after the removal treatment was terminated there were no significant differences between the control and experimental sites. Factor analysis showed that seasonal change was significant for all three food factors on the control sites, whereas on experimental sites the change was significant only for factor 1. At the middle successional stage (3.5 years since last fire), P. gracilicaudatus showed relatively small seasonal changes on both control and experimental sites, and significant differences between the control and experimental sites did not occur until after the removal manipulation was completed, showing a delayed response. Comparisons of the young and the middle successional stages on both control and experimental sites showed that P. gracilicaudatus used proportionally different food when R. lutreolus was present, but consumed similar food when R. lutreolus was removed. These results suggest that R. lutreolus might have restricted the access of P. gracilicaudatus to better microhabitats, and hence to a better food supply. The ecological implication of these results is that the interpretation of observed population and community patterns must take into account the direct effects of species interactions.     

Early stages of Calluna vulgaris regeneration after burning of coastal heath in central Norway

Questions: How does Calluna vulgaris regenerate after burning wet and dry heaths of different age? Location: Central Norway. Methods: Patches of Calluna dominated old and young wet heath and old dry heath were burned. The mean temperatures reached in the categories of heath were measured. Cover, frequency, height and number of seedlings of Calluna were studied in plots. Results: The mean burning temperatures varied from 680 to 740°C, and were highest in wet heath that had not been burned for at least 50 years. Regeneration of Calluna was evident in the year of burning, but only from seeds. Even heath with a short burning interval lacked vegetative regeneration. Calluna cover increased yearly and exceeded 50 % three years after burning. Regeneration was evident in the year of burning, and was highest in heath with a short burning interval. The height increased regularly at all sites, but was most rapid in dry heath, probably because of better microclimatic conditions. There were more seedlings in the heath with a short burning interval. Conclusions: Calluna only regenerates from seeds afterburning in central Norway. The density of Calluna increased rapidly, which is positive for the conservation and management of coastal heaths in central Norway.     

Limiting climatic factors and habitats of Erica tetralix at the eastern edge of its distribution range

We determined the limiting climatic factors, as well as the preferred habitats, of Erica tetralix L. at the eastern limit of its distribution range in the eastern Baltic region. It was found that E. tetralix in this region is a typical bog woodland plant preferring the wettest Sphagnum‐rich sites. Northern Atlantic wet heath fragments, base‐rich fens and species‐rich Nardus grasslands were other habitats for the species. The species composition in E. tetralix habitats resembled that found in appropriate habitats within its main distribution range, although the habitats in the eastern Baltic region lack many Atlantic floristic elements characteristic of wet heath. A generalised linear model describing the climatic niche of E. tetralix in Latvia suggests that mild winters, which exhibit a combination of a shallow maximum depth of soil freezing and a large number of days when the air temperature exceeds 0°C, as well as abundant annual and winter precipitation, are the main factors allowing the presence of E. tetralix in Latvia. The climate parameters at the eastern limit of the species’ distribution range are consistent with those recorded as being suitable for E. tetralix elsewhere. Our results reveal a strong relationship between oceanity and the distribution of E. tetralix. The climatic niche model suggests more climatically suitable areas in the Coastal Lowland geobotanical region where the species could potentially be found, most likely in bog woodlands. The future prospects to restore open areas of northern Atlantic wet heath with E. tetralix in Latvia are poor due to the decline in traditional land‐use; these areas have turned into bog woodlands or been converted into agricultural land.     

Population regulation and dispersion of the smoky mouse,Pseudomys fumeus I. Dietary determinants of microhabitat preference

Habitat preferences of four species of small mammals were studied on a 7.5-hectare trapping grid in a subalpine heathland/woodland complex on Mt William, western Victoria. Animals did not show strong spatial separation and differences in dispersion appeared to represent response to some feature of habitat. Floristic cues were good predictors of preference for Rattus lutreolus, Antechinus swainsonii and Pseudomys fumeus. Structural factors might also be important for R. lutreolus and A. swainsonii. The entire grid was suboptimal for Antechinus stuartii. Pseudomys fumeus was mycophagous during winter and, in the summer breeding season, principally ate seeds and bogong moths. Habitat preferences appear to reflect selection for those areas providing a year round source of high quality food rich in nitrogen. The transition period between the end of production of fungal sporocarps and prolific subalpine flower and seed production during summer may be particularly important as preferred areas provide fungi and seeds over longer periods, and food for bogong moths during their annual migration.     

Fine‐scale microhabitat selection for dense vegetation in a heathland rodent,Rattus lutreolus: Insights from intraspecific and temporal patterns

Abstract Vegetation is a dynamic habitat component and successional changes in vegetation structure can lead to concomitant changes in the communities of animals living in a particular area. Heathland rodents are a classic example, with vegetation at different ages post fire being dominated by different species. While broad associations are often demonstrated between the distribution and abundance of species and vegetation structure, the causal relationships are poorly understood. Studies of temporal and sex‐ or age‐specific patterns can provide strong insights into the processes underling patterns of habitat selection. In an attempt to better understand the mechanistic links between rodent successional patterns and vegetation structure in heathlands, we conducted a detailed study of microhabitat use by the swamp rat, Rattus lutreolus, in a native heathland in south‐eastern Australia. Rattus lutreolus typically occurs in late‐succession heath and is frequently associated with high vegetation density. Our assessment of vegetation at trapping stations, and also along trails used by the animals (using the spool‐and‐line tracking technique), revealed strong selection by the rats for dense vegetation by both day and night. The spool‐and‐line tracking approach revealed distinct intraspecific and temporal patterns. During the day, females foraged in vegetation of much higher density than did juveniles, with males behaving intermediately. During the night, however, all animals selected dense vegetation irrespective of sex or age, although the mean density of vegetation selected during the night was lower than it was during the day. These patterns were independent of daily maximum and minimum air temperature and were therefore unlikely to be related to microclimate. We propose instead that high vegetation density acts as a source of protection from predators, allowing R. lutreolus to forage safely both by day and by night.     

Subhabitat variability: A key to the high reptile diversity in chenopod shrublands

Abstract The herpetofauna of one hectare of chenopod shrubland near Roxby Downs in arid South Australia was studied from January 1991 until June 1993. The subhabitat preferences of 27 reptile species and one frog species were investigated by analysing capture rates, from more than 1800 captures in 401 pit traps. Although the site was characterized by relatively uniform cover of the dominant plant species Atriplex vesicaria, significant variation occurred in rock cover, and in edaphic and floristic features. Ctenophorus fordi, Ctenotus brooksi and Lerista labialis were strongly associated with sandy regions while Tympanocryptis intima, Diplodactylus tessellatus and Ctenotus strauchii were largely restricted to rocky subhabitats. Ctenotus leonhardii was strongly associated with a high density of Maireana species. Subhabitat preference of some of these species could be explained by the defence strategies they employed. Several species such as Ctenophorus nuchalis, Pogona vitticeps, Tympanocryptis lineata, Diplodactylus stenodactylus, Rhynchoedura ornata, Menetia greyii and Neobatrachus centralis were subhabitat generalists within the study site. The biological appropriateness of using a smaller number of subhabitat groupings, rather than the square root of the number of study sites, was confirmed in this study. Five subhabitat groups yielded meaningful preference data for more species than did 10 or 20 groups, and did not lose resolution achieved through higher level clustering.     

The carabid communities on peat and upland grasslands in northern England

During a two year period 13498 individuals of 66 species of carabids were taken from 44 sites on peat and upland grasslands over an altitude range of 11-847 m in the north of England. The similarities between the carabid faunas of each site have been assessed using a modified form of the Sørensen's Index and the sites clustered according to their similarities. Five carabid communities on peat and three on mineral soils have been identified and the more abundant species have been used to characterise them. Peat Community I occurs on dry heath and is characterised by peat associated species such as Trichocellus cognatus and Bradycellus ruficollis together with widespread open habitat species such as Pterostichus madidus, Notiophilus aquaticus, Calathus melanocephalus and Nebria salina. Peat Community II is found on areas where dry heath and deep wet peat are adjacent and is characterised by the species already mentioned together with typical wet habitat species such as Pterostichus diligens, P. nigrita, Patrobus assimilis. Agonum fuliginosum. Peat Community III is found on blanket bog and is characterised by the wet habitat species in the absence of the species present on the dry heath. Peat Community IV found on the lowland oligotrophic mires is characterised by the small number of species present and the addition of Pterostichus niger and Agonum ericeti to the few wet habitat species present. Peat Community V, on the scarp slope of Dun Fell, consists of the wet habitat species of Peat Community III together with Pterostichus madidus. Nebria salina, Notiophilus aquaticus and Calathus melanocephalus. Grassland Community I, on the fell tops, is characterised by the presence of Nebria gyllenhali, Notiophilus germinyi and Patrobus assimitis. Grassland Community II and III are less clearly defined but Grassland Community II may be present on wetter sites than III and is characterised by the presence of Pterostichus nigrita, P. diligens and P. strennus together with Notiophilus biguttatus. N. aquaticus, Pterosfichus madidus and Patrobus afrorufus. Grassland Community III consists of the latter group of species together with Nebria salina, Calathus melanocephalus and Notiophilus aestuans. The number of grassland sites studied was small and there may be further communities on the upland grasslands.     

Plant coexistence in coastal heaths: Habitat segregation in the post-fire environment

Abstract Previous studies of heaths on Pleistocene coastal sands showed consistent variation in patterns of floristic composition between areas on ridges and slopes but not within them. A large wild-fire that swept this system provided an opportunity to observe temporal processes in habitat segregation of species. Ridges and slopes were found to differ in species richness of seedlings in 0.0625 m2 quadrats and there was no evidence that the species richness in the two habitats was converging over 3 years. This suggests that initially these processes differ in space between the two habitats with more species in the wet heath being packed into a smaller area than in the dry heath. Seed-banks of species did not saturate available space for recruitment in either habitat, but seedling densities differed asymmetrically between habitats across two pairs of species studied. Experimental manipulation of seeds among habitats also showed distinct differences in establishment and survival among representative species from different habitats. The presence of seed-banks of wet-heath species in dry heath suggested that recruitment of their seedlings may occur there, but experiments showed that seedlings that arise from them do not survive there. Conversely, although no seed-bank of either dry-heath species studied was found in wet heath, our manipulations showed that their seedlings could grow there. Thus, superficially, physiological tolerance appeared to limit regeneration of wet-heath species in dry heath. However, there appeared to be no physiological limit for dry-heath plants to survive in wet heath. This paper shows that segregation of species may operate at either of two stages of the life cycle: at dispersal when safe sites for establishment are required, and at recruitment after seedlings have established. These findings highlight the importance of the regeneration niche in structuring community composition in coastal heaths, and contrast with traditional explanations of species segregation invoking physiological tolerance and competition at later life-history stages.     

Small mammal responses to pyric successional changes in eucalypt forest

Sixteen 1-ha study plots covering five regeneration stages were simultaneously trapped five times over a 20-month period to provide data on small mammal response to vegetation changes following fire. Areas regenerating after fires from 9 years to 1 month before the investigation were sampled in a uniform open forest on a coastal sand plain. Two types of understorey were recognized: one dominated by true forest shrubs with which Rattus fuscipes, Antechinus stuartii and Sminthopsis murina were associated, and another dominated by heath elements where the addition of Pseudomys novaehollandiae and Mus musculus produced a significantly more diverse small mammal community. The two communities exhibited different responses to post-fire vegetation changes. Rattus fuscipes was the most abundant species and showed a logistic growth in biomass. No resident populations were established in the first 3 years, but a rapid increase in biomass occurred from 3 to 5 years to plateau after 8 years. Regeneration age had the greatest effect on R. fuscipes biomass mediated through the amount of accumulated leaf litter with additional variation being attributed to several vegetation structure variables and plant species diversity. A replacement sequence in time was observed for species reaching their maximum abundance (P. novaehollandiae and/or M. musculus → S. murina → A. stuartii → R. fuscipes) and was interpreted as species occupying stages in the succession when their optimal habitat requirements were fulfilled. These results have important implications for the design of management policies using fire or fire regimes as tools for habitat maintenance or alteration. A mosaic of forest patches of adequate size covering the entire range of seral stages is necessary to meet the optimum requirements of all the above species.     

Edge effects and extinction proneness in a herpetofauna from Madagascar

Edge effects are thought to play a key role in fragmented habitats. It is often assumed that edge-avoiding species are more prone to local extinction than non-edge-avoiding species, but there are few data to support this assumption. Also, few data are available on the effects of edges on some groups, and there is little understanding of seasonal changes in edge effect intensity. To better understand the role that edge effects play in fragmented tropical forests, we assessed the distribution of reptiles and amphibians in six littoral rainforest fragments in southeastern Madagascar in 1999 (dry season) and 2000 (wet season). Using randomization tests, we found all three types of edge responses: edge-avoiders, interior-avoiders, and omnipresent species. However, edge responses varied considerably among seasons. For example, some species (e.g., Mantidactylus bicalcaratus, Phelsuma quadriocellata) were strong edge-avoiders in the dry season, but showed no preference for edge or interior habitats during the wet season. Also, edge-avoiding species tended to be more extinction-prone than non-edge-avoiding species. Abiotic data documented significantly higher temperatures and dew point temperatures near edges. Wind speed also tended to be higher and relative humidity tended to be lower near edges. Our results indicate that many amphibians and reptiles respond to altered microclimates near edges and these responses have a strong seasonal component. For many species, edge sensitivity does seem to be correlated with extinction vulnerability and therefore should be of primary consideration in plans to conserve biodiversity in fragmented tropical forests.