Frugivory by introduced black rats (Rattus rattus) promotes dispersal of invasive plant seeds

Oceanic islands have been colonized by numerous non-native and invasive plants and animals. An understanding of the degree to which introduced rats (Rattus spp.) may be spreading or destroying seeds of invasive plants can improve our knowledge of plant-animal interactions, and assist efforts to control invasive species. Feeding trials in which fruits and seeds were offered to wild-caught rats were used to assess the effects of the most common rat, the black rat (R. rattus), on 25 of the most problematic invasive plant species in the Hawaiian Islands. Rats ate pericarps (fruit tissues) and seeds of most species, and the impacts on these plants ranged from potential dispersal of small-seeded (≤1.5 mm length) species via gut passage (e.g., Clidemia hirta, Buddleia asiatica, Ficus microcarpa, Miconia calvescens, Rubus rosifolius) to predation where <15% of the seeds survived (e.g., Bischofia javanica, Casuarina equisetifolia, Prosopis pallida, Setaria palmifolia). Rats consumed proportionally more seed mass of the smaller fruits and seeds than the larger ones, but fruit and seed size did not predict seed survival following rat interactions. Although invasive rat control efforts focus on native species protection, non-native plant species, especially those with small seeds that may pass internally through rats, also deserve rat control in order to help limit the spread of such seeds. Black rats may be facilitating the spread of many of the most problematic invasive plants through frugivory and seed dispersal in Hawaii and in other ecosystems where rats and plants have been introduced.     

Multi level ecological fitting: indirect life cycles are not a barrier to host switching and invasion

Many invasive species are able to escape from coevolved enemies and thus enjoy a competitive advantage over native species. However, during the invasion phase, non‐native species must overcome many ecological and/or physiological hurdles before they become established and spread in their new habitats. This may explain why most introduced species either fail to establish or remain as rare interstitials in their new ranges. Studies focusing on invasive species have been based on plants or animals where establishment requires the possession of preadapted traits from their native ranges that enables them to establish and spread in their new habitats. The possession of preadapted traits that facilitate the exploitation of novel resources or to colonize novel habitats is known as ‘ecological fitting’. Some species have evolved traits and life histories that reflect highly intimate associations with very specific types of habitats or niches. For these species, their phenological windows are narrow, and thus the ability to colonize non‐native habitats requires that a number of conditions need to be met in accordance with their more specialized life histories. Some of the strongest examples of more complex ecological fitting involve invasive parasites that require different animal hosts to complete their life cycles. For instance, the giant liver fluke, Fascioloides magna, is a major parasite of several species of ungulates in North America. The species exhibits a life cycle whereby newly hatched larvae must find suitable intermediate hosts (freshwater snails) and mature larvae, definitive hosts (ungulates). Intermediate and definitive host ranges of F. magna in its native range are low in number, yet this parasite has been successfully introduced into Europe where it has become a parasite of native European snails and deer. We discuss how the ability of these parasites to overcome multiple ecophysiological barriers represents an excellent example of ‘multiple‐level ecological fitting’.     

Comparative isotopic natural history of two native passerines (Troglodytes cobbi and Cinclodes antarcticus) and the invasive rats (Rattus norvegicus) that extirpate them

While several studies have shown that invasive rats can have negative effects on island birds through predation (both direct predation and nest predation), other mechanisms for the effects of invasives on island biota have been given less attention. Here, we explore another potential mechanism by which invasive rats can affect native island birds: the competitive use of common resources. We used stable isotope analyses to estimate the fraction of marine and terrestrial sources incorporated into the tissues of two species of passerines (Troglodytes cobbi, Troglodytidae; and Cinclodes antarcticus, Furnariidae) and Norway rats (Rattus norvegicus, Muridae) in the Falkland Islands. These two passerines are absent on islands where rats are present. We found significant incorporation of marine resources in the three species, with the highest incorporation in tissues of T. cobbi. This species appears to be one of the passerines most reliant on marine sources and the most marine member of the family Troglodytidae. We also used the results of these isotopic analyses to estimate the isotopic niche breadth of each of these species and the isotopic niche overlap among them. Rattus norvegicus had a large isotopic niche that overlapped broadly with those of the two passerine species. We propose that different ways of both depicting and estimating isotopic niche widths are complementary rather than alternative. Our results are consistent with the notion that invasive rats might have an impact on these two species of Falkland Island passerines by using common resources but do not rule out the possibility that part of their effect is through direct predation.     

外来种入侵的过程、机理和预测

生物入侵是指某种生物从原来的分布区域扩展到一个新的（通常也是遥远的）地区,在新的区域里,其后代可以繁殖、扩散并持续维持下去,生物入侵成功的原因,即与入侵者本身的生物学,生态学特征有关,也与群落的脆弱性有关,入侵者可能较本地种的竞争能力强,更适应当地的环境,有的入侵者还可以改变环境,使之对已有利,而不利于本地种。缺乏天敌制约。群落的稳定性低和异常的环境扰动往往导致生物入侵,生物入侵的预测包括哪一种外来种会变成入侵种？哪些生态系统区域会被入侵？影响程度如何？入侵种的扩散态势如何等内容,对有关的理论和模型作了评介。     

Has the introduction of brown trout altered disease patterns in native New Zealand fish?

1. It is well recognised that non-indigenous species (NIS) can affect native communities via the 'spillover' of introduced parasites. However, two other potentially important processes, the 'spillback' of native parasites from a competent NIS host, where the latter acts as a reservoir leading to amplified infection in native hosts, and the 'dilution' of parasitism by a NIS host acting as a sink for native parasites, have either not been tested or largely overlooked.
2. We surveyed the helminth parasite fauna of native New Zealand fish in Otago streams that varied in the abundance of introduced brown trout Salmo trutta , to look for evidence of spillback and/or dilution. Spillover is not an issue in this system, with trout introduced as parasite-free eggs.
3. Seven native parasite species were present across 12 sites; significant inverse relationships with an index of trout abundance (i.e. dilution) were documented for three species infecting the native upland bully Gobiomorphus breviceps , and one species infecting the native roundhead galaxias Galaxias anomalus .
4. An inverse relationship between bully energy status and infection intensity of one parasite species suggests that parasite dilution could have positive effects on bully populations. Our failure to detect similar relationships for the other parasites does not preclude the possibility that dilution is beneficial to native fish, since parasites may have subtle or unmeasured impacts.
5. The parasite dilution patterns reported are compelling in that they occurred across several native host and parasite species; as such they have important implications for invasion ecology, providing an interesting contrast to the largely negative impacts reported for NIS. Mechanisms potentially responsible for the patterns observed are discussed.     

A complete history of the establishment of Japanese sika deer on the Delmarva Peninsula: 100 years post-introduction

While many non-native species immediately express their negative qualities which encourage their management (even attempted eradication), some have long lag periods before the population begins to grow out of control. Sika deer have been problematic in many places where they were introduced as novelties or games species through hybridization or aggressive interactions with native deer. In attempt to better manage these species we need to know their native ecosystem. We provide evidence through summarized literature of the manner in which sika deer arrived on Delmarva from Yakushima Island in Japan via a multi-generational stopover in the United Kingdom. We also add morphological and genetic support that confirm the origins and help describe the path of introduction of sika deer to Maryland. We also summarize the growth and change in population size(s) over the last 100 years. This historic understanding is an essential part of coping with the persistent growth of a large, aggressive herbivore that is currently being managed as a game species. We summarize the possible impacts of sika deer including the displacement of native white-tailed deer. The management of this species needs to be carefully observed as they continue to spread throughout the critical saltmarsh of the Delmarva Peninsula.     

Introgressive hybridization and species turnover in reservoirs: a case study involving endemic and invasive basses (Centrarchidae: <Emphasis Type="Italic">Micropterus</Emphasis>) in southeastern North America

Invasive species threaten native taxa with extirpation and extinction via several biological mechanisms. One such mechanism, hybridization and subsequent introgression of invasive alleles into native genomes is a serious concern, especially for taxa displaying weak reproductive barriers, as is the case for black basses. Black basses introduced outside of their native ranges thus pose elevated threats to endemic congeners, particularly in the southern United States where restricted ranges preclude refuge from introgression. The recently delineated Bartram’s bass (M. sp. cf M. coosae) is endemic to the upper regions of the Savannah River basin, throughout which anthropogenic modification, including impoundment, has been extensive. Non-native Alabama bass (M. henshalli) and smallmouth bass (M. dolomieu) have been introduced into this system on multiple occasions and now threaten Bartram’s bass via introgression. In this study we sampled four reservoirs (Jocassee, Keowee, Hartwell, and Russell) in the upper Savannah River during 2004 and 2010. Results from three codominant nuclear loci and one mitochondrial locus revealed extensive introgression between Alabama and Bartram’s bass. Results show that Alabama bass have replaced Bartram’s bass in lakes Keowee and Russell, where they were first introduced, while the frequencies of hybrids in lakes Jocassee and Hartwell are increasing. Hybridization involving Bartram’s bass with native largemouth bass and introduced smallmouth bass was detected in very low frequencies. Results highlight the importance of continual study over geographic and temporal scales to inform management and conservation of rare fishes threatened with extinction via interspecific hybridization.     

The ants of remote Polynesia revisited

The islands of remote Polynesia (east of Rotuma, Samoa, Tonga and New Zealand) have long been thought to contain few, if any, native ants. The findings of recent sediment core studies, however, challenge this conventional wisdom and indicate some species may be native. The majority of ant species in remote Polynesia, however, are introductions from tropical and subtropical regions around the world. Despite this diversity of origins, and the lack of a common coevolutionary history in the region, patterns of organization in remote Polynesian ant communities are generally similar to those observed in coevolved continental areas. The distribution of ant species across Polynesia is consistent with a primary mechanism of anthropogenic introductions, with the availability of suitable habitat as a secondary mechanism. The species-area relationship for better-collected Polynesian islands reveals these islands are depauperate compared to Melanesian islands with endemic species. Four out of five of the “world’s worst” invasive ant species are present in remote Polynesia. Recent studies have documented how range expansions of such ant species have had detrimental effects on native arthropod populations, although the overall effects of introduced ants per se on naïve endemic island arthropods may never be known with certainty. Considering the relatively fragile nature of island ecosystems, and the potential transformative effects of invasive ants on arthropod communities, vigilance is required to prevent the spread of invasive ant species across Polynesia.     

Investigating temporal changes in hybridization and introgression in a predominantly bimodal hybridizing population of invasive sika (Cervus nippon) and native red deer (C. elaphus) on the Kintyre Peninsula,Scotland

We investigated temporal changes in hybridization and introgression between native red deer (Cervus elaphus) and invasive Japanese sika (Cervus nippon) on the Kintyre Peninsula, Scotland, over 15 years, through analysis of 1513 samples of deer at 20 microsatellite loci and a mtDNA marker. We found no evidence that either the proportion of recent hybrids, or the levels of introgression had changed over the study period. Nevertheless, in one population where the two species have been in contact since ～1970, 44% of individuals sampled during the study were hybrids. This suggests that hybridization between these species can proceed fairly rapidly. By analysing the number of alleles that have introgressed from polymorphic red deer into the genetically homogenous sika population, we reconstructed the haplotypes of red deer alleles introduced by backcrossing. Five separate hybridization events could account for all the recently hybridized sika‐like individuals found across a large section of the Peninsula. Although we demonstrate that low rates of F1 hybridization can lead to substantial introgression, the progress of hybridization and introgression appears to be unpredictable over the short timescales.     

Assessing habitat suitability for the translocation of Ochrosia tahitensis (Apocynaceae), a critically endangered endemic plant from the island of Tahiti (South Pacific)

Reintroduction or translocation of threatened plant species, as part of in situ conservation efforts, often failed because of the lack or the poor quality of remaining natural habitats due to human disturbances and invasion by alien species, especially in island ecosystems. We conducted a study on Ochrosia tahitensis (Apocynaceae), a critically endangered endemic small tree in the tropical high volcanic island of Tahiti (French Polynesia, South Pacific) to find the most suitable sites for future translocation. Distribution models were produced based on climate, topography, and plant community inventories (i.e. species composition and abundance, canopy height and openness, basal area of woody species) of the few remnant populations. Results show that this species, comprising 32 reproductive trees within 16 populations known in the wild, remains restricted to a few ecological refuges representing a very small part of its potential ecological range located on the northwest side of the island, and shares its current habitats with a set of more common native woody species found in mesic-wet forests. The use of native plant communities as a proxy for habitat suitability along with species distribution modelling can enhance translocation success in island ecosystems, but only if the major threats causing population decrease, mainly forest destruction and fragmentation and invasive alien species, are effectively managed.     

Responses to terrestrial nest predators by endemic and introduced Hawaiian birds

Birds free from nest predators for long periods may either lose the ability to recognize and respond to predators or retain antipredator responses if they are not too costly. How these alternate scenarios play out has rarely been investigated in an avian community whose members have different evolutionary histories. We presented models of two nest predators (rat and snake) and a negative control (tree branch) to birds on Hawai?i Island. Endemic Hawaiian birds evolved in the absence of terrestrial predators until rats were introduced approximately 1,000 years ago. Introduced birds evolved with diverse predator communities including mammals and snakes, but since their introduction onto the island approximately one century ago have been free from snake predation. We found that (a) endemic and introduced birds had higher agitation scores toward the rat model compared with the branch, and (b) none of the endemic birds reacted to the snake model, while one introduced bird, the Red‐billed Leiothrix (Leiothrix lutea), reacted as strongly to the snake as to the rat. Overall, endemic and introduced birds differ in their response to predators, but some endemic birds have the capacity to recognize and respond to introduced rats, and one introduced bird species retained recognition of snake predators from which they had been free for nearly a century, while another apparently lost that ability. Our results indicate that the retention or loss of predator recognition by introduced and endemic island birds is variable, shaped by each species' unique history, ecology, and the potential interplay of genetic drift, and that endemic Hawaiian birds could be especially vulnerable to introduced snake predators.     

Assessing biogeographical relationships of ecologically related species using favourability functions: a case study on British deer

Aim Using six free‐living deer species in Great Britain as a case study, we studied biogeographical relationships of ecologically related species composed of both native and introduced species. Location Great Britain. Methods  We modelled the environmental favourability for the deer species using variables related with spatial location, climate, topography, human disturbances and habitat structure. Favourability values of each pair of native (naturalized)‐introduced species were used to estimate the fuzzy overlap index (FOvI) as a measure of overall similarity between the environmental requirements for the species in Great Britain. The absolute local overlap values (FOvI‐L) were also used to measure the degree to which a given location was favourable simultaneously for each pair of species. We assessed the trends of species favourability across a range defined by the absolute local overlap values and studied the shape of the obtained curves since they informs us about the favourability balance between the studied species. Results Muntjac and Chinese water deer attained higher favourability values than native species in localities with intermediate values of FOvI‐L (a reduced number in the study area), suggesting that if competitive relationships were established in these localities the introduced deer species may have some advantages over natives. Sika deer only achieved higher values than fallow deer in those localities clearly unfavourable for the naturalized species. Our analyses predicted that fallow deer will be less affected by the introduced deer species than native species. Main conclusions We developed an approach based on the favourability function to describe biogeographical relationships between species, natives and introduced and to assess from a biogeographical perspective if introduced species could pose a competitive risk to natives. Although the results of present analyses do not conclusively demonstrate competitive exclusion, they provide directional hypotheses that can be tested in experimental field and laboratory studies.     

Crossing the (Wallace) line: local abundance and distribution of mammals across biogeographic barriers

Past and ongoing vertebrate introductions threaten to rearrange ecological communities in the Indo‐Malay Archipelago, one of Earth's most biodiverse regions. But the consequences of these translocations are difficult to predict. We compared local abundance and distributions in four tropical mammal lineages that have crossed from Asia to Wallacea or New Guinea. The local abundance of macaques (Macaca spp.), which naturally crossed Wallace's Line, was higher in Sulawesi (east of the line; mean = 3.7 individuals per camera station, 95% CI = 2.2: 5.1) than in Borneo (west of the line; mean = 1.1, CI = 0.8: 1.4), but the local abundance of Malay civets (Viverra tangalunga), Rusa deer, and Sus pigs was similar in their native ranges and where they had been introduced by humans east of Wallace's Line. Proximity to rivers increased Malay Civet local abundance and decreased the local abundance of pigs in parts of their introduced ranges (Maluku and New Guinea, respectively), while having no effect on local abundance in their native ranges (Borneo) or other areas where they have been introduced (Sulawesi). That local abundance was higher east of Wallace's Line in just one of four mammal lineages is consistent with findings from plant invasions, where most species have similar abundance in their native and introduced ranges. However, species’ ecology may change as they enter new communities, for example, their patterns of abundance at local scales. This could make it difficult to predict community structure in the face of ongoing species introductions.     

Improved design method for biosecurity surveillance and early detection of non-indigenous rats

A recent advance in biosecurity surveillance design aims to benefit island conservation through early and improved detection of incursions by non-indigenous species. The novel aspects of the design are that it achieves a specified power of detection in a cost-managed system, while acknowledging heterogeneity of risk in the study area and stratifying the area to target surveillance deployment. The design also utilises a variety of surveillance system components, such as formal scientific surveys, trapping methods, and incidental sightings by non-biologist observers. These advances in design were applied to black rats (Rattus rattus) representing the group of invasive rats including R. norvegicus, and R. exulans, which are potential threats to Barrow Island, Australia, a high value conservation nature reserve where a proposed liquefied natural gas development is a potential source of incursions. Rats are important to consider as they are prevalent invaders worldwide, difficult to detect early when present in low numbers, and able to spread and establish relatively quickly after arrival. The ?exemplar? design for the black rat is then applied in a manner that enables the detection of a range of non-indigenous species of rat that could potentially be introduced. Many of the design decisions were based on expert opinion as data gaps exist in empirical data. The surveillance system was able to take into account factors such as collateral effects on native species, the availability of limited resources on an offshore island, financial costs, demands on expertise and other logistical constraints. We demonstrate the flexibility and robustness of the surveillance system and discuss how it could be updated as empirical data are collected to supplement expert opinion and provide a basis for adaptive management. Overall, the surveillance system promotes an efficient use of resources while providing defined power to detect early rat incursions, translating to reduced environmental, resourcing and financial costs.     

Disease and competition,not just predation,as drivers of impacts of the black rat (Rattus rattus) on island mammals

Hanna & Cardillo (2014) report an association between the presence of black rats (Rattus rattus) and extinctions of endemic mammals on Australian islands. Although we agree that introductions of the black rat are likely to have had a significant impact on island ecosystems, we suggest that there is little empirical support for their main conclusion, that predation (and thus mesopredator processes) is the causal mechanism driving the association between the presence of black rats and extinctions of native mammals on Australian islands. We present a brief literature review of evidence for two alternative mechanisms – introduction of novel diseases and competition – which suggest there are multiple explanations for how native mammal extinctions on Australian islands may have occurred. The potential impact of these processes interacting across different trophic levels is rarely considered, but is applicable across many different ecosystems world‐wide.     

Enemy release or invasional meltdown? Deer preference for exotic and native trees on Isla Victoria,Argentina

Abstract How interactions between exotic species affect invasion impact is a fundamental issue on both theoretical and applied grounds. Exotics can facilitate establishment and invasion of other exotics (invasional meltdown) or they can restrict them by re‐establishing natural population control (as predicted by the enemy‐release hypothesis). We studied forest invasion on an Argentinean island where 43 species of Pinaceae, including 60% of the world's recorded invasive Pinaceae, were introduced c. 1920 but where few species are colonizing pristine areas. In this area two species of Palearctic deer, natural enemies of most Pinaceae, were introduced 80 years ago. Expecting deer to help to control the exotics, we conducted a cafeteria experiment to assess deer preferences among the two dominant native species (a conifer, Austrocedrus chilensis, and a broadleaf, Nothofagus dombeyi) and two widely introduced exotic tree species (Pseudotsuga menziesii and Pinus ponderosa). Deer browsed much more intensively on native species than on exotic conifers, in terms of number of individuals attacked and degree of browsing. Deer preference for natives could potentially facilitate invasion by exotic pines. However, we hypothesize that the low rates of invasion currently observed can result at least partly from high densities of exotic deer, which, despite their preference for natives, can prevent establishment of both native and exotic trees. Other factors, not mutually exclusive, could produce the observed pattern. Our results underscore the difficulty of predicting how one introduced species will effect impact of another one.     

Possible roles of introduced plants for native vertebrate conservation: the case of Madagascar

Restoration approaches rely on native plants; yet in some situations, natural vegetation may not grow fast enough to prevent the fragmentation of original vegetation and the consequent negative impacts on fauna. In this context, some introduced plants may grow faster and provide more food than native species, and they may also contribute to human livelihood. We investigate to what extent introduced plant species (1) can serve as habitat and food for endemic vertebrates and (2) provide benefits to local people. We address this question in Madagascar, characterized by high degrees of endemism, long histories of coevolution between endemic species, highly fragmented forests, and a high reliance of the rural population on natural resources. A literature search for interactions between endemic fauna and introduced flora revealed that 100 of 1,379 introduced species recorded for Madagascar are used by endemic vertebrates. They provide food mainly for primates, flying foxes, and birds, and habitat for all terrestrial vertebrate groups. One hundred vertebrate species were reported to use introduced plants, many of which are fast growing and are useful for populations. Although these introduced plants should be approached with caution due to their potentially invasive behavior, many introduced plants can provide services for the native fauna and for humans. For example, trees can provide an interim solution to secure the survival of endemic fauna that otherwise would be lost due to fragmentation effects. These plants could bridge the time lag until native forest regeneration or restoration with native trees will have become effective.     

The invasion and potential impact of the Asian House Gecko (Hemidactylus frenatus) in Australia

Hemidactylus frenatus is an Asian gecko that has spread pantropically to become one the world's most widespread reptiles. It has been established in Australia for approximately 50 years, but the last two decades have seen massive range expansion across settled areas of northern and eastern Australia; and this spread continues at pace. Disturbingly, H. frenatus is increasingly being detected in natural habitats in Australia, in some cases at high densities. Despite rampant spread, there has been little concern regarding the potential impact of this species on native geckos or natural systems more broadly. This is surprising given that Australia is a centre of gecko origin and diversity, and that H. frenatus has had well documented detrimental impacts on geckos in other parts of its introduced range. Here I review the biology and global distribution of H. frenatus, plot its spread in Australia over the five decades since establishment, and review the research on invasive populations of this species overseas and in Australia to assess potential impacts. I argue that Australia should be more concerned about H. Frenatus because: (i) it is spreading rapidly across northern, eastern and central Australia; (ii) it can invade natural habitats; (iii) it is a very strong competitor and may out‐compete Australian geckos in some situations; and (iv) it carries novel parasites that may impact native reptile species. Hemidactylus frenatus is here to stay and represents a potential threat to Australia's diversity and ecology. A key question is the degree to which it will invade natural habitats and what its impacts will be in these. Research is required to assess the current and potential impacts of H. frenatus in Australia so as to determine how these can be managed and the level of investment warranted.     

Differential population responses of native and alien rodents to an invasive predator,habitat alteration and plant masting

Invasive species and anthropogenic habitat alteration are major drivers of biodiversity loss. When multiple invasive species occupy different trophic levels, removing an invasive predator might cause unexpected outcomes owing to complex interactions among native and non-native prey. Moreover, external factors such as habitat alteration and resource availability can affect such dynamics. We hypothesized that native and non-native prey respond differently to an invasive predator, habitat alteration and bottom-up effects. To test the hypothesis, we used Bayesian state-space modelling to analyse 8-year data on the spatio-temporal patterns of two endemic rat species and the non-native black rat in response to the continual removal of the invasive small Indian mongoose on Amami Island, Japan. Despite low reproductive potentials, the endemic rats recovered better after mongoose removal than did the black rat. The endemic species appeared to be vulnerable to predation by mongooses, whose eradication increased the abundances of the endemic rats, but not of the black rat. Habitat alteration increased the black rat''s carrying capacity, but decreased those of the endemic species. We propose that spatio-temporal monitoring data from eradication programmes will clarify the underlying ecological impacts of land-use change and invasive species, and will be useful for future habitat management.     

Competitive naïveté between a highly successful invader and a functionally similar native species

Naïveté can occur within any novel antagonistic interaction, and competitive forces play a fundamental role in shaping community structure, yet competitive naïveté has received very little attention in the literature to date. Naïveté towards a novel competitor is unlikely to result in immediate mortality, but could potentially affect access to resources and hence population growth and survival. In cases where only one species (either native or alien) remains naïve to the other, the species that recognizes the other will gain advantage, with implications for both the persistence of the native species and the establishment and spread of the invasive. The invasive black rat (Rattus rattus) has spread throughout many coastal areas of Australia, and competes with the native bush rat (Rattus fuscipes) wherever they coexist. As these rats have now been interacting for approximately 200 years, and multi-species rodent communities generally maintain their structure through olfactory communication, our aim was to determine whether these two very closely related species recognize one another’s odors and use them to mediate their interactions. We used remote-sensing cameras deployed in single- and mixed-species sites to record the behavioral responses of each species to conspecific, heterospecific and control odors. Black rats investigated bush rat odors but not vice versa, suggesting that bush rats may remain naïve towards their new competitor. Highly successful invaders such as black rats may possess traits such as broad recognition templates and rapid learning capabilities that contribute to their ongoing success in invading new environments.