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Ecosystems worldwide are increasingly being invaded by multiple species, and the rate of biological invasion is accelerating, leading to more interactions among invasive species. One such interaction that has received little attention is the phenomenon of 'serial replacement' or 'over-invasion', where an established invasive species is supplanted by a second invasive species. Understanding this interaction is important as controlling the second species could inadvertently lead to an increase in the abundance of the first species. We used a hierarchical state-space model to analyse changes in annual abundances (commercial catch-per-unit-effort) of three invasive fish species, tench (Tinca tinca), common carp (Cyprinus carpio) and redfin perch (Perca fluviatilis), in the Murray-Darling River system (MDRS), Australia between 1954–2002. Tench were present at low abundances until the mid-1970 s, before declining to the point of no commercial catch post-1989. This rapid decline coincided with a significant increase in carp abundance, suggesting that carp may have driven the tench decline through habitat modification (particularly the destruction of aquatic plants), consistent with findings from European studies that show the disappearance of tench from ponds with intensive carp farming. Redfin perch populations, were inferred to be much less impacted by the invading carp population. While carp were present in the MDRS for the duration of the study, the rapid increase in carp abundance in the early 1970 s coincided with the introduction of a specific genetic lineage—the "Boolarra strain". Our analysis provides compelling evidence of serial replacement of long-established tench by invading common carp triggered by the introduction of a novel carp strain. [ABSTRACT FROM AUTHOR]

Non-native deer are becoming increasingly common in peri-urban landscapes, where they pose a risk to the health and wellbeing of people. Professional vehicle-based shooting is commonly used to control deer populations in these complex landscapes, but the effectiveness and cost of this method have seldom been evaluated. We analyzed the effectiveness and cost of using professional vehicle-based shooting to reduce the abundance and impacts of non-native rusa deer (Cervus timorensis) in a peri-urban landscape in Wollongong, eastern Australia, during 2011–2021. We incorporated the results from an independent monitoring program into a Bayesian joint-likelihood framework to model spatio-temporal changes in rusa deer abundance. Finally, we used our findings to assess the effect of the management program on the number of complaints from the residents. After eleven years and the removal of 4701 rusa deer from Wollongong LGA (712 km2), deer abundance did not change in 74.7% of the area, decreased in 19.4% of the area (mostly in and around the sites where the professional shooting occurred), and increased in 5.9% of the area. Shooting was most cost-effective during winter when the longer hours of darkness meant that shooters could visit more sites. In contrast to deer abundance, the probability of residents complaining about deer increased in space and time. Our study shows that professional vehicle-based shooting can locally reduce the abundance of invasive deer in a peri-urban landscape, providing that sufficient control effort is expended. We suggest that shooting effort is currently too thinly spread across this peri-urban landscape, and that concentrating shooting effort on the areas of greatest deer abundance and resident complaints might be a more cost-effective strategy for managing invasive deer in peri-urban landscapes. [ABSTRACT FROM AUTHOR]

Deer populations and their impacts on forest ecosystems are increasing globally. Given the imperative and expense to mitigate impacts of invasive deer, we aimed to elucidate critical drivers of (i) deer density, (ii) deer impacts, and (iii) the relationship between them, to facilitate targeted management. We used quantile regression forests to model deer density (faecal pellet counts at 1948 locations) and impacts (browsing and other impacts on > 23,000 woody plants at 343 locations) across a mosaic of agricultural and forested ecosystems in Victoria, Australia (12,775 km2). Climate, topography, vegetation cover, and distance to water features were included as model covariates. Modelled deer density (r2 = 0.71, MAE = 0.56 pellets/m2) was most influenced by distance to waterbodies (> 10 ha, 31.2%), elevation (14.3%) and woody vegetation cover (12.9%). Modelled deer impact (r2 = 0.32, MAE = 6.9%) was most influenced by deer density (21.0%), mean annual precipitation (12.8%) and elevation (12.2%). Deer density was typically highest near large waterbodies, at low elevation, and with intermediate tree cover (40–70%). Impacts increased steadily with deer density up to ~ 2 pellets/m2. Our study demonstrates the importance of forest water and forest agricultural interfaces for both deer density and impacts. Deer are likely to be most abundant near waterbodies due to the availability of high-quality forage and water, and prefer lowland locations that have access to both open and forested habitats. Spatial models can be used to predict deer density and associated impacts to facilitate targeted invasive deer management. [ABSTRACT FROM AUTHOR]

Sleeper populations of non-native species can remain at low abundance for decades before irrupting. For over a century, fallow deer (Dama dama) in the island state of Tasmania, Australia, remained at low abundance and close to the region in which they were released. Recently, there are indications the population has increased in abundance and distribution. Here, we spatially quantify the population change using a time series of annual spotlight counts from 1985 to 2019 (up to 172 transects annually, totalling of 5756 transect counts). Next, we predict the potential for further range expansion, using global occurrences to characterise the species' climatic niche, and remote-camera surveys (3225 camera sites) to model fine-grained habitat suitability. Spotlight counts of fallow deer increased by 11.5% annually, resulting in a 40-fold increase from 1985 to 2019. The core distribution increased 2.9-fold during this 35-year period, and now spans c. 27% of Tasmania's land area. Satellite populations have established in locations where farmed deer have escaped or been released, suggesting that humans have facilitated range expansion via new introduction events. Based on climate and habitat suitability, our models predict that 56% of Tasmania is suitable under the current climate. This suggests range expansion is likely to continue unless the population is actively managed, which could include the eradication of satellite populations and containment of core populations. This case study cautions that despite over a century of slow population growth, sleeper populations of non-native species can abruptly increase. [ABSTRACT FROM AUTHOR]

Life history theory predicts trade-offs in allocation between survival, maintenance, growth, and reproduction, especially when resources are scarce. Individual variation in resource acquisition can affect trade-offs, but is often unaccounted for. We quantified the fitness costs of reproduction, accounting for environmental conditions, maternal characteristics and individual variation. We analyzed 10 years of data from marked kangaroos to evaluate how reproductive allocation affected annual mass change and skeletal growth, subsequent fecundity and weaning success, and survival, accounting for maternal mass or size and forage availability. Through repeated measurements of 76–91 females, we investigated how trade-offs varied within and between individuals, assessing whether individual variation could mask population-level trade-offs. In poor environments, females that weaned an offspring lost mass. Females that nursed an offspring for > 7 months had reduced skeletal growth. Females that did not gain mass over the previous 12 months rarely reproduced, especially if they had nursed an offspring for > 7 months the previous year. Reproductive allocation had no effect on weaning success, which was very low, and did not affect maternal survival, suggesting a conservative strategy. Disentangling within- and between-individual responses revealed trade-offs within individuals, but because individuals did not vary in their responses to earlier effort, these trade-offs did not drive population trends. The interacting effects of environmental conditions, maternal characteristics and individual variation on allocation trade-offs demonstrate the importance of long-term monitoring for understanding life history variations in changing environments. [ABSTRACT FROM AUTHOR]

The factors affecting variation in the abundances of invasive mammal species have seldom been evaluated at large spatial scales. We used data collected in a large-scale biodiversity monitoring program to identify variables predicting abundances of common brushtail possums (Trichosurus vulpecula; ‘possum’), a marsupial folivore introduced to New Zealand in the 1800s. We sampled possum abundances, vegetation structure and composition, and abiotic variables at 395 spatially representative sites in natural forest on the North, South and Stewart islands. Records of possum control were obtained from management agencies. The large sample size enabled us to consider the relative importance of 27 variables for possum abundances. Twelve variables explained 80% of the contributions to the final boosted regression tree model. Control history had the largest contribution to the model, with sites subject to aerial 1080 poison baiting either once or more than once in the previous 7 years having possum abundances 64% and 74% lower, respectively, than sites without control. Possum abundances were also negatively related to humidity, stem density, tree cover density, slope, elevation and distance to pasture/crop. Abundances increased with increasing food plant species richness, Weinmannia racemosa (a preferred food tree) cover, and solar radiation. There was an interaction between longitude and control history. We conclude that invasive possum abundances in New Zealand’s natural forests are determined by multiple biotic and abiotic factors, sometimes in interaction. Recent control operations, however, have greatly reduced possum abundances. Increasing the spatial extent of aerial 1080 poison baiting will further reduce possum abundances in New Zealand forests. [ABSTRACT FROM AUTHOR]

There has long been debate regarding the primacy of bottom-up and top-down effects as factors shaping ecosystems. The exploitation ecosystems hypothesis (EEH) predicts that predators indirectly benefit plants because their top-down effects limit herbivores’ consumption of plants, and that the strength of trophic cascade increases with increasing primary productivity. However, in arid environments, pulses of primary productivity produced by irregular rainfall events could decouple herbivore–plant and predator–prey dynamics if high conversion efficiency from seed biomass to consumers allows the rapid build-up of consumer populations. Here, we test predictions of the EEH in an arid environment. We measured activity/abundances of dingoes, red kangaroos and grasses, and diet of dingoes, in landscapes where dingoes were culled or not culled over 3 years. Dingo activity was correlated with rainfall, and their tracks were less frequent at culled sites. Kangaroo abundance was greater at sites where dingoes were culled and increased with rainfall in the previous 6 months. Grass cover was greater at sites where dingoes were not culled and increased with rainfall in the previous 3 months. During a period of average rainfall, dingoes primarily consumed rodents and increased their consumption of kangaroos during a period of drier conditions. Our results are consistent with the hypothesis that suppression of an apex predator triggers a trophic cascade, but are at odds with the EEH’s prediction that the magnitude of trophic cascades should increase with primary productivity. Our study demonstrates that temporal fluctuations in primary productivity can have effects on biomasses of plants and consumers which are in many ways analogous to those observed along spatial gradients of primary productivity. [ABSTRACT FROM AUTHOR]

Endozoochory by exotic mammalian herbivores could modify vegetation composition by facilitating the dispersal and establishment of exotic and native plant species. We examined the potential for endozoochoric dispersal of native and exotic plants by exotic hog deer ( Axis porcinus) in south-eastern Australia. We quantified the germinable seed content of hog deer faecal pellets collected in five vegetation types within a 10,500-ha study area that was representative of their Australian range. Twenty exotic and 22 native species germinated from hog deer faecal pellets and significantly more native species germinated compared to exotic species. Seedlings of the encroaching native shrub Acacia longifolia var. sophorae emerged, but no native trees emerged and the percentage of grasses that germinated was low (11%). The species composition of germinants was similar among the five vegetation types. We estimated that the hog deer population in our study area could potentially disperse >130,000 viable seeds daily. Our study shows how an exotic mammal can disperse seeds from both native and invasive plants and highlights the need for endozoochory to be considered more widely in studies assessing the impacts of exotic mammals on plant communities. [ABSTRACT FROM AUTHOR]

There is anecdotal evidence that increasing densities of Himalayan tahr ( Hemitragus jemlahicus) are associated with declining densities of chamois ( Rupicapra rupicapra) in the Southern Alps, New Zealand. To examine this phenomenon, densities of tahr and chamois were measured at 53 sites within their sympatric range in the eastern Southern Alps during 1978–1979. In sites where only one species was present, tahr density was significantly higher than chamois density ( P=0.032), probably reflecting species differences in sociality. Chamois density was higher in catchments without tahr than in those with tahr ( P=0.012). Similarly, tahr density was significantly higher at sites without chamois than at those with chamois ( P=0.033). Sites with both species present (termed sympatric) were significantly larger than those with only chamois or tahr ( P<0.001). Following the prohibition of aerial hunting of tahr in 1983, 16 of the 17 sites where tahr and chamois were sympatric during 1978–1979 were recounted during 1991–1996. There was a 6-fold increase in the mean density of tahr between the two counts ( P=0.001), whereas chamois density had declined significantly ( P=0.006). Chamois persisted at only three sites, two of which had the highest chamois densities in 1978–1979. This is evidence that increasing densities of tahr exclude chamois from all but the `best' habitats. We conclude that intensive aerial hunting of tahr during 1967–1983 reduced tahr densities such that chamois could co-exist with tahr. [ABSTRACT FROM AUTHOR]

Unfortunately, the online publication contained an error in the "Data availability statement" and it is corrected by this erratum. [ABSTRACT FROM AUTHOR]

Abstract: Environmental variation affects foraging decisions and resources available for allocation among competing life-history traits. In seasonal environments, variation in breeding phenology leads to differences in relative timing of resource intake and expenditure, which can lead to variation in maternal allocation tactics. Monitoring maternal allocation to fetal growth in wild mammals is challenging, however, and few studies have linked seasonal effects of forage and maternal condition to early offspring development. Asynchronous parturition and short gestation make kangaroos ideal for studying phenological effects on very early growth, since pouch young born in different seasons can be measured during stages equivalent to in utero development for eutherian mammals. Over 4 years, we recaptured 68 eastern grey kangaroo mother-young pairs with parturition dates spanning 5 months to evaluate how birthdate affects maternal allocation to offspring growth before pouch exit. Structural equation modeling revealed that mothers that gave birth in autumn gained mass during lactation, and their young grew faster than young born in early summer. When later lactation coincided with poor winter forage and cold temperatures, mothers prioritized maintenance of their own mass over offspring growth. Differences in maternal mass change and allocation to early and late-born young suggest that seasonal resource availability influenced tactics of resource storage and expenditure. Our results provide a mechanistic link between reproductive phenology, seasonal forage, and allocation trade-offs in wild mammals, and demonstrate a clear effect of maternal mass change on growth of young during a phase that occurs in utero for eutherian mammals.Significance statement: Capital and income breeding are often presented as opposing tactics of resource provisioning. Many species, however, use a combination of stored and concurrent resources to reproduce. In seasonal environments, reproductive phenology should affect the relative timing of resource acquisition and expenditure, which could affect maternal allocation to offspring. We used repeated captures of mother-young kangaroo pairs and path analysis to explain how maternal allocation tactics adjust to season of parturition. Mothers that timed later lactation with cold weather and low winter forage relied more heavily on stored resources for reproduction and allocated less to offspring growth. Flexibility in foraging tactics may explain the variability in kangaroo parturition date by allowing mothers to use stored energy to sustain reproduction during periods of scarce forage. [ABSTRACT FROM AUTHOR]