Habitat Accommodation Model Research Articles

Some like it burnt: species differences in small mammal assemblage in a Mediterranean basin nearly 3 years after a major fire

The habitat accommodation model (HAM) is a theoretical framework that predicts wildlife community recovery based on their habitat requirements. While post-fire habitat-related research is well documented in the Mediterranean basin, studies specifically focusing on HAM are scarce. Here, we described the small mammal assemblage in a Mediterranean area ~3 years after a fire, specifically examining three functional small mammalian categories: ground-foraging insectivorous, ground-foraging herbivorous/granivorous, and arboreal-foraging species. The study was conducted in Monte Pisano (Italy), where fire burnt ~12 km2 in September 2018. A stratified random sampling was adopted, basing on burnt status and forest type. In each of the 50 sites, during late spring-summer 2021, 12 hair-tubes were deployed, and collected hairs were taxa-attributed based on morphology. A presence/absence dataset was built, and db-RDA was used to explore assemblage composition, and single-species occupancy models to test specific hypotheses. The relative abundance of ground-foraging herbivorous/granivorous was higher in the burnt area, characterised by a dense undergrowth, which could be related to anti-predatory strategies and food opportunities. Insectivorous could be in a recolonisation phase, masking their earlier absence, which could explain why their abundance was not associated with any factor tested. Arboreal-foraging species were associated with forest type, indicating a primary role for tree cover and other factors such as rocky cover and likely in situ survival. The HAM was overall confirmed also in Mediterranean basin ecosystems. This may facilitate predictions about post-fire animal successions, which in turn may provide valuable insights into post-fire management practices and biodiversity conservation strategies.

Fire-mediated habitat change regulates woodland bird species and functional group occurrence.

In an era characterized by recurrent large wildfires in many parts of the globe, there is a critical need to understand how animal species respond to fires, the rates at which populations can recover, and the functional changes fires may cause. Using quantified changes in habitat parameters over a ~400-yr post-fire chronosequence in an obligate-seeding Australian eucalypt woodland, we build and test predictions of how birds, as individual species and aggregated into functional groups according to their use of specific habitat resources, respond to time since fire. Individual bird species exhibited four generalized response types to time since fire: incline, decline, delayed, and bell. All significant relationships between bird functional group richness or abundance and time since fire were consistent with predictions based on known time-since-fire-associated changes in habitat features putatively important for these bird groups. Consequently, we argue that the bird community is responding to post-fire successional changes in habitat as per the habitat accommodation model, rather than to time since fire per se, and that our functional framework will be of value in predicting bird responses to future disturbances in this and other obligate-seeder forest and woodland ecosystems. Most bird species and functional groups that were affected by time since fire were associated with long-unburned woodlands. In the context of recent large, stand-replacement wildfires that have affected a substantial proportion of obligate-seeder eucalypt woodlands, and the multi-century timescales over which post-fire succession occurs, it would appear preferable from a bird conservation perspective if fires initiating loss of currently long-unburned woodlands were minimized. Once long-unburned woodlands are transformed by fire into recently burned woodlands, there is limited scope for alternative management interventions to accelerate the rate of habitat development after fire, or supplement the resources formerly provided to birds by long-unburned woodlands, with the limited exception of augmenting hollow availability for key hollow-nesting species.

Decadal post-fire succession of soil invertebrate communities is dependent on the soil surface properties in a northern temperate forest

Although fires are common disturbances in North American forests, the extent to which soil invertebrate assemblages recover from burning remains unclear. Here, we examine long-term (14- to 101-yr) recoveries of soil invertebrate communities from common cut and burn treatments conducted at 6 to 26-yr intervals since 1911 in a deciduous forest in the upper Great Lakes region (USA). We characterize soil surface macro-invertebrate communities during both fall and spring across a long-term, experimental fire chronosequence to characterize invertebrate community recovery at decadal time-scales and community changes between seasons. We posited that changes in invertebrate community structure might, in turn, impact decomposition process. We sampled active organisms at the soil surface using pitfall traps. We described understory vegetation, measured soil properties, and conducted a 4-year litter bag study with big-toothed aspen leaves (Populus grandidentata). Invertebrate community responses followed a habitat accommodation model of succession showing that invertebrate succession is dependent on the soil surface properties. The fall and spring measures revealed that the densities of active invertebrates were highest 101 years after fire. For a given pair of stands, a pattern of sharing higher percentage of taxa was denoted when stands were of similar age. Some species such as the beetle Stelidota octomaculata appeared to be indicator of the chronosequence succession stage because it tracks the successional increase of Quercus and acorn production at the study site. We also found a significant positive correlation between leaf decomposition of soil macrofaunal accessible leaves and millipedes density across the chronosequence. We show that vegetation cover changes and related shifts in habitat structure occurring during post-fire succession are important in shaping communities assemblages. This finding highlights the importance of simultaneously considering abiotic-biotic factors together with above- and belowground measurements to better characterize controls on successional community dynamics after disturbance.

Small Mammal Abundance in Mountain Big Sagebrush Communities after Fire and Vegetation Recovery

Abstract. Managing fire for the conservation of biodiversity is a widespread challenge. An important disturbance mechanism in big sagebrush (Artemisia tridentata) communities, fire has well-known effects on vegetation structure but poorly described consequences for sagebrush wildlife communities. We estimated the abundance of small mammals in relation to fire history in mountain big sagebrush (A. t. ssp. vaseyana) communities by way of a chronosequence approach that included 3 wildfires and adjacent unburned areas. We compared patterns of mammal community succession with expectations of the habitat accommodation model by associating responses of mammals to change over time in vegetation structure. Burned study sites were at various stages of vegetation succession from 7 to 19 years following fire. Shrub canopy cover ranged from 9% to 36% and was not fully recovered on the plots at 19 years after fire. Only Belding's ground squirrel (Urocitellus beldingi) demonstrated a measurable response to fire that was...

Recent decline of an endangered, endemic rodent: does exclusion of disturbance play a role for Hastings River mouse (Pseudomys oralis)?

Context The role of disturbance and its exclusion is fundamental to the conservation of threatened species. Aims We used the habitat accommodation model as a framework to investigate the importance of forest disturbance for the endangered Hastings River mouse, Pseudomys oralis, focusing on timber harvesting. Methods Our study comprised two separate surveys. We resurveyed old survey sites (n = 24) where the species was originally recorded as either present (logging excluded) or absent (subsequently logged). A second survey targeted trapping in high-quality habitat stratified by different times since logging. Finally, we analysed a 15-year trapping dataset targeting P. oralis to assess associations with co-occurring species. Key results The resurvey of old sites resulted in 12 P. oralis individuals being trapped, compared with 46 individuals in original surveys. Substantial declines were observed over time in transects where logging was excluded (60–82% decline), whereas there was little change at transects where P. oralis was not previously trapped and that were subsequently logged. The second survey yielded 27 P. oralis captures at post-logging sites assessed as high quality. Occupancy was very high (ψ = 0.93 ± 0.21) in transects logged 7–15 years ago and was 60% less in transects where logging was excluded for 35–45 years (ψ = 0.37 ± 0.22), whereas occupancy in transects logged 2–6 years ago was intermediate. This pattern of higher occupancy in logged areas was mirrored for the mean number of P. oralis trapped per transect. Ordination of habitat data showed an association of P. oralis with heath, mat-rushes and logs, whereas rats (Rattus and Melomys) were associated with ferns and shrubs. Camera traps revealed low background levels of predator presence. A negative exponential relationship was found between probability of occupancy of P. oralis and rat abundance from a 15-year trapping dataset (44 275 trap-nights), suggesting that rats may compete with P. oralis. Conclusions Our results supported the habitat accommodation model and suggested that disturbance is likely to influence the persistence of P. oralis. However, an interaction between predation and loss of cover from high-frequency disturbance (fire or intense grazing) cannot be excluded as a key threat. Implications Disturbance should be incorporated into the management of some species. Adaptive monitoring is recommended to assess alternative management regimes.

Contrasts in short- and long-term responses of Mediterranean reptile species to fire and habitat structure.

Changes in habitat structure constitute a major factor explaining responses of reptiles to fire. However, few studies have examined habitat factors that covary with fire-history variables to explain reptile responses. We hypothesise that more complex habitats should support richer reptile communities, and that species-specific relative abundance should be related to particular habitat features. From spring 2012-2014, twenty-five transects were surveyed in the Albera Region (north-east Iberia). The vegetation structure was measured and the extent of habitat types in a 1000-m buffer around each transect calculated. Reptile-community metrics (species richness and reptile abundance) were related to fire history, vegetation structure, and habitat types, using generalized additive models. These metrics correlated with habitat-structure variables but not with fire history. The number of species increased with more complex habitats but decreased with pine-plantation abundance in the 1000-m buffer. We found contrasting responses among reptiles in terms of time since fire and those responses differed according to vegetation variables and habitat types. An unplanned fire in August 2012 provided the opportunity to compare reptile abundance values between pre-fire and the short term (1-2 years) after the fire. Most species exhibited a negative short-term response to the 2012 fire except Tarentola mauritanica, a gecko that inhabits large rocks, as opposed to other ground-dwelling species. In the reptiles studied, contrasting responses to time since fire are consistent with the habitat-accommodation model of succession. These differences are linked to specific microhabitat preferences and suggest that functional traits can be used to predict species-specific responses to fire.

Multi-century dynamics of ant communities following fire in Mediterranean-climate woodlands: Are changes congruent with vegetation succession?

As vegetation recovers after disturbances such as fire its composition and structure systematically changes, affecting the availability of resources for fauna and mediating physical conditions. According to the habitat accommodation model, these changes drive a succession of animal species, which enter and leave according to their habitat requirements. While the response of ants to fire has been extensively studied, studies of ant communities in biomes with long fire-return intervals have been overwhelmingly short-term in nature. Here, we explore the response of ant species, functional groups and communities to time since fire using a uniquely long-term (>300years) chronosequence in eucalypt woodlands of south-western Australia. Marked non-monotonic vegetation structural changes occur in non-resprouting Eucalyptussalubris-dominated woodlands following fire, with tree and ground fuel cover peaking at intermediate periods post-fire. Hence, we predicted that changes in the occurrence of Dominant Dolichoderinae, Hot-Climate Specialist and Cold-Climate Specialist functional groups would mirror the non-monotonic changes in habitat complexity, as predicted by the habitat accommodation model. Overall ant species richness and composition did not show clear post-fire successional patterns, with extensive spatial turnover a likely factor. However, richness and abundance of ant functional groups broadly responded as predicted, with Dominant Dolichoderinae and Hot-Climate Specialists more prominent in more-open recently-burnt and long-unburnt habitat, and Cold-Climate Specialists more prominent in less open habitat at an intermediate time since fire. This matching, non-monotonic temporal pattern of changes in ant functional groups and vegetation structure suggests that ant functional group occurrence is mediated through changes in habitat, as posited by the habitat accommodation model, and not simply time since disturbance. Current fire management in E. salubris woodlands aims to minimise wildfire occurrence, which is consistent with the maintenance of ant functional diversity at a regional scale given the long time periods over which changes occur post-fire. The combination of recent large wildfires and predicted fire-facilitating climate changes suggest that future shifts in the relative dominance of ant functional groups are likely if fire management is unsuccessful in limiting wildfires occurring in mature woodlands.

Taxonomic and functional response of a Mediterranean reptile assemblage to a repeated fire regime

Wildfires are common disturbances that have a major impact on ecosystems. Recent decades have seen an increase in fire frequency and extension due to the combined effects of climate change and land-use history. We studied the taxonomic and functional response of a reptile assemblage to repeated fires in southern France to understand shifts in dominant species and diversity, as well as the mechanisms that underlie responses according to functional traits of species. In the spring of 2010, we sampled reptiles in areas with three types of fire regime: unburned, burned once (2003) and burned 4–5 times (last fire in 2003) along a fire history of 51-years period. With this field sampling design, we examined the intermediate disturbance hypothesis and the habitat accommodation model of succession as methods to predict reptile responses to natural fire regimes. We also compared habitat structure at the study area between 1944 and 2006 to certify that repeated-fire regimes have modified the habitat for reptiles. The comparison of the habitat structure between both periods demonstrated that repeated-fire regimes modified the landscape from a homogeneous sparse forest to a contrasted heterogeneous mixture of scrubland and dense forest. We found a loss of reptile diversity after one and multiple fires, a result that contradicts the intermediate disturbance hypothesis. Reptile composition differed among the three fire regimes: there was a shift in dominant species and a reduction of beta diversity related to an increase in the number of fires. We also observed a functional response to repeated fires, with an increased frequency of insectivorous reptiles, which live in open areas, are specialists in their ecological niche, and have a short lifespan. These results suggest that reptile replacement according to fire regime accounts for a habitat accommodation model following particular traits of species. Our study indicated that areas subjected to repeated fires have a more strictly Mediterranean reptile assemblage than unburned areas, due to the ability of Mediterranean species to survive thermal environments in open (burned) areas. At a regional scale, changes in dominant species between unburned and repeatedly burned areas might be an argument for maintaining a patchwork of areas burned at variable intervals. However, the increase in fire frequency and extension suggests a future scenario of extinction for species negatively impacted by fire, such as the endangered Hermann’s tortoise Testudo hermanni, for which the study area is home to one of the last native populations in the western Mediterranean.

Small reptile community responses to rotational logging

Timber harvesting is a common global disturbance that has important effects on the ability of forests to provide ecosystems services and retain biodiversity. Using predictive frameworks to examine biodiversity responses to logging could assist in retaining natural forest values. The intermediate disturbance hypothesis (IDH) and the habitat accommodation model (HAM) potentially offer frameworks for explaining different coarse scale community responses to logging. We used a 60year post-logging chronosequence to investigate small reptile community responses to age post-logging in temperate forests using three metrics (species richness, evenness and relative abundance). First, we evaluated if variation in these metrics adhered to prior predictions, including the IDH. Second, we evaluated how age post-logging influence community responses through fine scale vegetation elements. Third, we evaluated support for the HAM by measuring compositional change (species turnover) of small reptile community to age post-logging. Reptile relative abundance exhibited a curvilinear relationship to age since logging, contradicting our prior prediction of sustained increase. Species richness and evenness were unrelated to age since logging thus providing no support to IDH and other prior predictions. Relative abundance and richness did not relate to any vegetation characteristic tested. These metrics were also unrelated to logging method. Community composition was marginally significantly influenced by age since logging, thus supporting the HAM. Our results suggest that forest reptiles exposed to logging exhibit variable changes depending on the community metric in question, and that different approaches, including those based on species traits, are needed to improve evaluating disturbance related biodiversity responses.

Evaluating the role of fire disturbance in structuring small reptile communities in temperate forests

Fire is an integral disturbance shaping forest community dynamics over large scales. However, understanding the relationship between fire induced habitat disturbance and biodiversity remain equivocal. Ecological theories including the intermediate disturbance hypothesis (IDH) and the habitat accommodation model (HAM) offer predictive frameworks that could explain faunal responses to fire disturbances. We used an 80 year post-fire chronosequence to investigate small reptile community responses to fires in temperate forests across 74 sites. First, we evaluated if changes in species richness, abundance and evenness post-fire followed trends of prior predictions, including the IDH. Second, using competing models of fine scale habitat elements we evaluated the specific ways which fire influenced small reptiles. Third, we evaluated support for the HAM by examining compositional changes of reptile community post-fire. Relative abundance was positively correlated to age post-fire while richness and evenness showed no associations. The abundance trend was as expected based on the prior prediction of sustained population increase post-disturbance, but the trend for richness contradicted the prediction of highest diversity at intermediate levels of disturbance (according to IDH). Abundance changes were driven mainly by changes in overstorey, ground layer, and shelter, while richness and evenness did not associate with any vegetation parameter. Community composition was not strongly correlated to age since fire, thus support for the HAM was weak. Overall, in this ecosystem, frequent fire disturbances can be detrimental to small reptiles. Future studies utilizing approaches based on species traits could enhance our understanding of biodiversity patterns post-disturbance.

Fire, landscape change and models of small mammal habitat suitability at multiple spatial scales

AbstractFire is an important process in many ecosystems, but inappropriate fire regimes can adversely affect biodiversity. We identified a naturally flammable heathy woodland ecosystem where the use of planned fire had increased the extent of older vegetation, and quantified the abundance of two small native mammals in this landscape (silky mouse Pseudomys apodemoides and heath rat P. shortridgei). We defined four time‐since‐fire (TSF) categories representing a 2‐ to 55‐year post‐fire sequence and, on the basis of a habitat accommodation model, predicted that both species would select younger age‐classes over older ones. We also predicted that (i) much of the variance in vegetation structure would remain unexplained by TSF and (ii) statistical models of mammal abundance and occupancy including structural variables as predictors would be better than models including TSF. Pseudomys apodemoides selected 17‐ to 23‐year‐old sites, while there was no evidence that P. shortridgei selected a particular TSF category, findings that were inconsistent with our predictions. In line with our predictions, relatively large portions of the variance in vegetation structure remained unexplained by TSF (adjustedr2 for four structural variables: 0.24, 0.29, 0.35 and 0.57), and in three of four cases there was strong evidence that statistical models of mammal abundance and occupancy including structural variables were better than those including TSF. At the site scale (hectares), P. shortridgei abundance was positively related to the cover of dead material at the base of Xanthorrhoea plants and at the trap scale (metres), the trapability of both species was significantly related to vegetation volume at 0–20 cm. Our findings suggest that TSF may not be a good proxy for either vegetation structure or species abundance/occupancy.

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

AbstractThe 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.

How predictable are reptile responses to wildfire?

Natural disturbances are key processes in the vast majority of ecosystems and a range of ecological theories have been developed in an attempt to predict biotic responses to them. However, empirical support for these theories has been inconsistent and considerable additional work remains to be done to better understand the response of biodiversity to natural disturbance. We tested predictions from the intermediate disturbance hypothesis and the habitat accommodation model of succession for reptile responses to fire history and a single major fire event. We focused our work on a broad range of vegetation types spanning sedgeland to temperate rainforest located within a national park in south‐eastern Australia. We found no significant relationships between reptile species richness and the number of fires over the past 35 years, the time since the last fire, or the severity of a major fire in 2003. Thus, we found no strong evidence to support the intermediate disturbance hypothesis.A correspondence analysis of reptile assemblages revealed a gradient in species responses to fire history. However, we found limited evidence for an ordered succession of reptiles. Nor could the responses of individual species be readily predicted from life history attributes. Thus, our findings were generally not consistent with predictions from the habitat accommodation model of succession. A possible explanation for the absence of a predictable sequence of recovery following disturbance might be the rapidity of post‐fire recovery of many components of native vegetation cover that were found to be important for reptiles (e.g. the extent of grass cover). This would have limited the time for early successional conditions to prevail and limited opportunities for species associated with such conditions. We found that most reptile species responses were much more strongly linked to vegetation type than fire variables, emphasizing a need to understand relationships with vegetation before being able to understand possible fire effects (if and where they exist). We found the disturbance concepts we examined were limited in their ability to accurately predict reptile responses to past fire history or the impacts of a single major fire in 2003. Practical management might be best guided not by disturbance theory, but by carefully setting objectives to meet conservation goals for particular individual species of reptiles.

How many common reptile species are fire specialists? A replicated natural experiment highlights the predictive weakness of a fire succession model

Species with strong preferences for early or late successional stages after fire may be extinction prone under current fire regimes. However, the extent of specialisation to time since fire is poorly understood, and, for reptiles, succession models for predicting responses are in the development phase. In this study we tested predictions of a reptile succession model, and identified species that may be fire specialists. Reptiles were sampled in five burnt and unburnt mallee Eucalyptus woodlands, Australia. Two, 400 m transects within each burn treatment were sampled using 11 pairs of pitfall-traps that were opened for five weeks over two summers. A habitat accommodation model of succession that was previously developed for mallee reptiles correctly predicted the observed responses of three of 16 common reptile species. A further four species showed non-significant trends in the predicted direction. However, eight other species showed unexpected responses. One species showed a strong interaction between burn age and location, requiring a two-dimensional successional model in contrast with the usual linear models explaining reptile responses to fire. One third of common species were not affected by fire and so may not have increased risks of extinction due to the fire suppression/incineration cycle. However, approximately half to two-thirds of common reptiles did have a fire response, so the risk of deterministic extinction in small fragments may be substantial. Further model development is needed to better predict fire responses and to assist the design of fire mosaics that can accommodate early and late successional fire specialists.

Experimental manipulation of habitat structure: a retrogression of the small mammal succession

Summary The habitat accommodation model for animal succession proposed that animal species enter a succession when changes in the vegetation succession reach a threshold of habitat suitable to that species. As the vegetation succession moves on, the habitat becomes less suited to that species and it is competitively excluded by species better suited to the habitat. The main species in the mammalian succession following fire for wet heath in eastern Australia are rodents, with Pseudomys gracilicaudatus (eastern chestnut mouse) being followed by Rattus lutreolus (swamp rat) which becomes dominant with increasing time since fire. The abundance of both species has been shown to correlate with vegetation density, but in markedly different ways, and asymmetric interspecific competition has been demonstrated using controlled, replicated removal experiments in the field. We used this system to examine if vegetation density is causal, manipulating the habitat by clipping to remove 60–70% of the vegetative cover from the 10 m × 10 m area surrounding each of six trapping stations on each grid. There were four experimental plots clipped, each with two abutting grids, one clipped and one unclipped, and a further four control plots each with two abutting grids that remained undisturbed. We monitored the effects on each species with three censuses in January 1993 (summer) before clipping in early February, and on five further censuses, three in February (late summer) to assess immediate, short‐term effects, one in August (winter) and one in December 1993 (early summer). The abundance of Rattus lutreolus was significantly reduced by clipping the vegetation, while the abundance of Pseudomys gracilicaudatus remained relatively unchanged by the clipping. Two species that are abundant on early succession stages in dry heath succession, but occurred at very low abundance on these wet heath habitats before clipping, P. novaehollandiae (New Holland mouse) and Mus domesticus (house mouse), showed marked increases in abundance on clipped and control plots soon after clipping. An abundance index based on the standardized difference between clipped and control plots, was used to assess responses to habitat manipulation. Rattus lutreolus demonstrated significant negative index values, Pseudomys gracilicaudatus had index values close to zero until the winter census, P. novaehollandiae and Mus domesticus showed positive abundance indices soon after clipping. The order of significant responses to the habitat manipulation was revealed as: Mus domesticus→Pseudomys novaehollandiae→ P. gracilicaudatus→ Rattus lutreolus. The impact of a habitat manipulation experiment on these four species of rodents produced a retrogression of the small‐mammal succession. This demonstrated a causal role for vegetation density, which provided insight into the mechanisms that operate during the succession following fire, and supported the habitat accommodation model for animal succession.

Experimental transplants of mice (Pseudomys and Mus) on to early stages of post‐mining regeneration in open forest

AbstractResults are presented for three controlled replicated experiments in which mice were transplanted onto the early successional stages of two regenerating mining paths. Naive house mice (Mus musculus) were successfully introduced on to sites regenerating for 8 years, with 56% remaining after 3 days and 2% still present after 69 days. Naive New Holland mice (Pseudomys novaehollandiae) had marginal establishment success on sites regenerating for 4.9 years, with 21% remaining after 3 days and 3% still present after 22 days. However, on sites regenerating for 3.9 years and 4.4 years, all 17 transplanted New Holland mice had dispersed from the treatment plots after 3 days. New Holland mice have been shown to be competitively dominant to house mice. Hence, we conclude that the reason New Holland mice do not colonize mining paths regenerating for less than 4.9 years is the unsuitability of the habitat rather than their exclusion by house mice. These results are consistent with the early stages of the mammalian succession following sand mining and fit the same habitat accommodation model proposed for post‐fire mammalian succession.

Experimental confirmation of interspecific competition between native and introduced mice

AbstractThis paper tests the hypothesis that Pseudomys novaehollandiae shows competitive superiority over Mus musculus. Experimental removals of P. novaehollandiae on four I ha treatment plots and additions on a further four I ha plots show significant effects of interspecific competition when compared to two I ha unmanipulated control plots. Significant effects of P. novachollandiae populations on the abundance of M. musculus populations were observed for number of captures/day, abundance/trapping session and for the recruitment of new individuals over the post‐removal period, thus allowing rejection of the null hypothesis in each case. There was an apparent ceiling on the total rodent abundance which is indicative of a resource limitation. The resource in short supply appears to be space, but it is not clear if the competition is for food or shelter resources contained within such space or for the space per se, but the latter seems less likely.The confirmation of this interspecific competition supports the inferences drawn from a considerable amount of indirect evidence, largely descriptive, obtained from previous studies in the Myall Lakes National Park. This study also shows that competition is one of the mechanisms controlling the replacement of species in the succession following disturbance and lends support to the habitat accommodation model proposed for such succession. These points support previous statements on the importance of interspecific competition as a determinant of the structure of these small‐mammal communities.

Fire and Mammalian Secondary Succession in an Australian Coastal Heath

A species—rich small—mammal community on 7 ha of diverse coastal heath in Myall Lakes National Park, New South Wales, Australia, was studied for 7 mo before the area burned in a wildfire (August 1974) and has subsequently been monitored for 5 yr since the fire. Species regularly trapped were the dasyurids Antechinus stuartii and Sminthopsis murina, the peramelid Isoodon macrourus, and the native murids Pseudomys novaehollandiae and P. gradcilicaudatus, together with the introduced Mus musculus. Pseudomys species, M. musculus, and S. murina reached greater abundance on early seral stages, while the abundance there of both Rattus fuscipes and R. lutreolus was much reduced. Species reach peak abundance in an orderly replacement sequence exhibiting a mammalian secondary succession. A habitat accommodation model is proposed with species entering the succession and reaching peak abundance as externally controlled changes in the vegetation fulfil the habitat requirements of each species. Species leave the succession or are greatly reduced in abundance when these local physical conditions move out of the optimal range for the species. This study shows that a major perturbation of a small—mammal community can produce a variety of responses among species, suggesting that regeneration time may represent a resource axis subdivided by community members in this secondary succession. The rapid recovery illustrated by the total number of individuals, as a measure of community response, support the suggestion that fire and fire frequency have been major factors in producing a fire—adapted, species—rich small—mammal community on this heathland.