Absence Of Terrestrial Predators Research Articles

Interactions between European rabbits and native marsupials in the absence of terrestrial predators

AbstractEuropean rabbits (Oryctolagus cuniculus) are ubiquitous across Australia and have the ability to influence native species directly and indirectly. Despite this, limited research focuses on interspecific interactions between rabbits and native mammals. We aimed to determine how site occupancy, detection probability, and temporal activity periods of native mammals changed in response to the presence or absence of rabbits. We monitored three native mammal species using 85 camera traps in a systematic grid at Mt Rothwell Conservation and Research Reserve (Victoria, Australia), a predator‐barrier fenced reserve with two distinct sections—an area with rabbits and an area without. Bettongs (rufous Aepyprymnus rufescens and eastern Bettongia gaimardi), eastern barred bandicoots (Perameles gunni), and southern brown bandicoots (Isoodon obesulus) had a naïve site occupancy of 71%, 42%, and 24%, respectively. Site occupancy for both bandicoot species decreased in areas with more clumping grass with eastern barred bandicoot occupancy increasing with leaf litter cover, and southern brown bandicoots with vegetation height. Rabbit presence did not influence site occupancy of any species. Species detection probabilities were generally positively associated with open vegetation and rabbit presence, except for southern brown bandicoots which were more detectable without rabbits. Both bandicoot species shifted their peak activity periods in the absence of rabbits having an earlier, and more defined activity peak. Our results demonstrate that the presence of rabbits in the absence of invasive predators may not influence the site occupancy of co‐occurring native mammals, however, could influence the behaviour of smaller co‐occurring mammals, either directly or indirectly.

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 Hawaiʻi 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.

Time allocation to resources by three species of rats (Rattus spp.) in a radial arm maze

Abstract ContextIntroduced rats (Rattus spp.) can pose a serious threat to native flora and fauna, especially on islands where most species have evolved in the absence of terrestrial predators. Effective detection and eradication methods for introduced rats are essential to the maintenance of insular ecosystem integrity. Thus, it is important to better understand the behaviour of rats when they first arrive in a new setting. AimsTo determine whether rats would find some novel stimuli to be significantly more attractive than other novel stimuli. MethodsAn eight-arm radial maze was used to study the behaviour of three species of Rattus finding themselves in a novel environment with various familiar and unfamiliar stimuli. Key resultsAlthough there were some differences in responses by species and by sex, most rats sought out and spent considerable time in the den box, suggesting an immediate need for security when in an unfamiliar setting. Rats also sought out faeces of conspecifics, suggesting the need for social contact or reproduction. The rats, which had not been food deprived, did not seem interested in food sources, although there was some attraction to the water source. ImplicationsThe management implications of the present study’s results are two-fold. First, appears that detection of newly arriving rats on islands would be aided by strategic placement of den boxes that are highly acceptable to rats. Managers could then inspect the den boxes periodically (or use a remote sensing system) for evidence of rat presence. Second, the den boxes could be scented with the faeces of other rats to further attract invading rats to the den boxes. This protocol might also hold the rats near the invasion site for a longer period of time before they begin seeking other shelter, food sources or mates. These protocols could give managers increased opportunities to detect any newly invading rats, and potentially increase the available time to deploy a rapid response to the invasion, before the animals begin to widely disperse. Of course, the rats will ultimately seek a source of palatable food, so placing durable, yet palatable, rodenticide bait in the den boxes might further decrease the probability of the invaders establishing a self-sustaining population.

The extreme insular adaptation of Garganornis ballmanni Meijer, 2014: a giant Anseriformes of the Neogene of the Mediterranean Basin.

New skeletal elements of the recently described endemic giant anseriform Garganornis ballmanni Meijer, 2014 are presented, coming from the type-area of the Gargano and from Scontrone, southern and central Italy, respectively. The new remains represent the first bird remains found at Scontrone so far, and another shared element between these two localities, both part of the Apulia-Abruzzi Palaeobioprovince. The presence of a very reduced carpometacarpus confirms its flightlessness, only previously supposed on the basis of the very large size, while the morphologies of tarsometatarsus and posterior phalanges clearly indicate the adaptation of G. ballmanni to a terrestrial, non-aquatic, lifestyle. Its very large body size is similar to that observed in different, heavily modified, insular waterfowl and has been normally interpreted as the response to the absence of terrestrial predators and a protection from the aerial ones. The presence of a carpal knob in the proximal carpometacarpus also indicates a fighting behaviour for this large terrestrial bird species.

Kelp Geese (Chloephaga hybrida) and Flightless Steamer-Ducks (Tachyeres pteneres) in the Beagle Channel: the importance of islands in providing nesting habitat

We describe the nest-site characteristics and breeding habitat use of Kelp Geese (Chloephaga hybrida) and Flightless Steamer-Ducks (Tachyeres pteneres) along 137 km of coastline on the northern shore of the Beagle Channel, Argentina, and 87 km of island coastline. We examined the importance of vegetation cover, predation, and tourism on the distribution of nests among islands. We found all nests only on islands and islets. Nesting sites for both species were strongly associated with higher proportions of high vegetation cover (shrubs). Kelp Geese were also associated with the absence of terrestrial predators. Tourist presence on islands was not associated with the occurrence of nests for either species. The northern coasts of the Beagle Channel and the islands and islets along the channel have similar habitat types. However, the islands and islets are relatively inaccessible to mammalian terrestrial predators compared to the coast of the channel where terrestrial predators are frequently recorded. Therefore, islands and islets seem to provide a relatively safe nesting habitat for Kelp Geese and Flightless Steamer-Ducks by offering refuge mainly from ground predators. Additionally, habitat changes caused by increased human disturbance along the northern shore of the Beagle Channel may also explain the presence of nests only on islands and islets, though further studies are needed to assess these effects. This study contributes new information on the breeding habitat and nesting sites of Flightless Steamer-Ducks and Kelp Geese in the Beagle Channel, to assist in the identification of priority breeding sites and habitats to protect. Also, it highlights the importance of islands and islets of the Beagle Channel as safe breeding refuge for these two ground nesting seabirds.

Seeing through the lizard’s trick: do avian predators avoid autotomous tails?

Abstract Counter-adaptations of predators towards their prey are a far less investigated phenomenon in predator-prey interactions. Caudal autotomy is generally considered an effective last-resort mechanism for evading predators. However, in victim-exploiter relationships, the efficacy of a strategy will obviously depend on the antagonist’s ability to counter it. In the logic of the predator-prey arms race, one would expect predators to develop attack strategies that minimize the chance of autotomy of the prey and damage on the predator. We tested whether avian predators preferred grasping lizards by their head. We constructed plasticine models of the Italian wall lizard (Podarcis sicula) and placed them in natural habitat of the species. Judging from counts of beak marks on the models, birds preferentially attack the head and might also avoid the tail and limb regions. While a preference for the head might not necessarily demonstrate tail and limb avoidance, this topic needs further exploration because it suggests that even unspecialised avian predators may see through the lizard’s trick-of-the-tail. This result may have implications for our understanding of the evolution of this peculiar defensive system and the loss or decreased tendency to shed the tail on island systems with the absence of terrestrial predators.

Influence of colony size on pup fitness and survival in South American sea lions

AbstractIncreased terrestrial pup mortality in small colonies due to harassment by subadult males has been proposed as a mechanism to explain the stagnation of South American sea lion populations after sealing ended. To test this hypothesis, pup survival rate was assessed in five northern Patagonia colonies with different sizes. Female diet quality as well as pup growth rate and immune status from the largest and smallest of these colonies were also assessed. Results indicated that the pup survival rate increased with colony size and pup‐to‐subadult male ratio. Furthermore, pups grew faster in the smallest colony, although female diet composition and pup immune status did not differ between the two colonies. Inverse relationship between pup growth rate and survival rate indicated that mortality was independent of food supply. In absence of terrestrial predators, infanticide by subadult males is the only mortality source other than starvation and illness and the relationship between pup survival rate and pup‐to‐subadult male ratio approached a type II functional response curve. Thus, infanticide stands as the most likely reason for the observed positive relationship between colony size and pup survival rate, supporting the hypothesis that post‐sealing population stasis was caused by inverse density dependence.

Vulnerability of ground-nesting waterbirds to predation by invasive American mink in the Cape Horn Biosphere Reserve, Chile

Biological invasions constitute one of the most important threats to biodiversity. This is especially true for “naïve” birds that have evolved in the absence of terrestrial predators in island ecosystems. The American mink ( Mustela vison) has recently established a feral population on Navarino Island (55°S), southern Chile, where it represents a new guild of terrestrial mammal predators. We investigated the impact of mink on ground-nesting coastal waterbirds with the aim of deriving a vulnerability profile for birds as a function of different breeding strategies, habitat, and nest characteristics. We compared rates of nest survival and mink predation on 102 nests of solitary nesting species ( Chloephaga picta, Tachyeres pteneres), on 361 nests of colonial birds ( Larus dominicanus, Larus scoresbii, Sterna hirundinacea), and on 558 artificial nests. We calculated relative mink and bird densities at all nest sites. Nests of colonial species showed the highest nest survival probabilities (67–84%) and no predation by mink. Nest survival rates for solitary nesting species were lower (5–20%) and mink predation rates higher (10–44%). Discriminant analyses revealed that mink preyed upon artificial nests mainly at shores with rocky outcroppings where mink were abundant. High nest concealment increased the probability for predation by mink. Conservation planning should consider that invasive mink might severely affect the reproduction success of bird species with the following characteristics: solitary nesting, nesting habitat at rocky outcrop shores, and concealed nests. We recommend that work starts immediately to control the mink population with a priority in the nesting habitats of vulnerable endemic waterbirds.

Invasive American mink Mustela vison in wetlands of the Cape Horn Biosphere Reserve, southern Chile: what are they eating?

The impact of alien American mink on the native fauna of oceanic islands has been demonstrated in a number of locations. In the sub-Antarctic Cape Horn Biosphere Reserve of southern Chile the species is currently expanding in an area where the native fauna evolved in the absence of terrestrial predators. To evaluate any emerging problems we therefore investigated seasonal variation in prey use by mink on Navarino Island within the Reserve. We identified undigested remains in 414 scats collected from the shores of 27 ponds over January–November 2006. Diet consisted mainly of mammals and birds. Mammals, including both native and exotic rodents, were the predominant prey in all seasons but birds were of equal importance during the summer (when birds breed and their abundance and diversity increases on the island). Exotic rodents were the only identifiable mammalian prey item during winter. Native wetland birds constituted a substantial proportion of mink diet, and greater than that reported in other areas. Many birds breeding on Navarino Island are ground-nesting, a strategy that evolved in the absence of native mammalian predators. Considering the international importance of this region, our results emphasize the need for an assessment of the impact of mink predation on the populations of native prey.

Differences in morphology, performance and behaviour between recently diverged populations of Podarcis sicula mirror differences in predation pressure

We investigated the possible role of variation in predation pressure in the phenotypic divergence of two island populations of the Italian wall lizard, Podarcis sicula. In 1971, ten adult specimens from the island of Pod Kopište (Adriatic Sea, Croatia) were transported to the island of Pod Mrčaru, 3.5 km east, where they founded a new population. Although the two islands resemble each other in general physiognomy (size, elevation, microclimate) and in the absence of terrestrial predators, lizards from the newly established population are now on average larger and have shorter hind limbs. They also exhibit lower maximal sprint speed as measured on a racetrack, and fatigue faster when chased in a torus track. In the field, lizards from the original population of Pod Kopište respond to a simulated predatory attack by fleeing at larger approach distances and by running further from the predator than lizards from Pod Mrčaru. These changes in morphology, behaviour and performance may result from the relaxed predation intensity on the latter island. Our analysis of the structural features of the microhabitats suggests that the vegetation on Pod Mrčaru offers more protection to lizards. Also, plasticine models of lizards, laid out on the islands, less often exhibited signs of being attacked by birds on Pod Mrčaru than on Pod Kopište. Our findings provide an example of how changes in (possibly a single) environmental factor may simultaneously produce responses in behaviour, morphology and whole‐animal physiology, and this on a surprisingly small spatial and temporal scale.

Browse site selection by snowshoe hares: effects of food supply and predation risk

If snowshoe hares (Lepus americanus Erxleben, 1777) change their foraging behaviour through the population cycle as food supply and predation pressure change, these shifts could contribute to their population cycles by affecting survival and reproduction. We examined whether hares change their foraging movements and browse site selection in response to manipulations of food addition and predator reduction during a cyclic low phase. Snowshoe hares on sites with supplemental rabbit chow ate fewer species per site and preferred to browse in slightly denser cover than unfed hares. Differences in foraging behaviour were linked to season and site characteristics. Snowshoe hares moved similar distances and spent similar amounts of time per browse site in the presence and absence of terrestrial predators. Hares protected from predators used slightly more browse sites in thick cover, but this pattern was partially due to differences in availability. The absence of terrestrial predators had little effect on snowshoe hare foraging behaviour; instead, browse distribution patterns explained most of the behavioural variation. Thus, the predicted patterns in response to the manipulations did not occur, and our results challenge the idea that changes in snowshoe hare foraging behaviour contribute to their cyclic dynamics.

Megafaunal extinction in the late Quaternary and the global overkill hypothesis

The global blitzkrieg hypothesis explains differential rates of megafaunal extinction between the world's landmasses in the late Quaternary based on a proposed leap in predation efficiency enjoyed by colonising societies. It is characterised by appealing simplicity. Selective over hunting, facilitated by naiveté to human predation, produced rapid mass extinctions of large animals wherever subsistence societies colonised new landmasses. Taken at face value the circumstantial case for blitzkrieg is compelling and despite a paucity of direct evidence it has gained considerable support. Our review of the model suggests that it overlooks much contradictory data and rests on simplistic interpretations of complex biogeographicat and anthropological phenomena. These interpretations and assumptions do not account for major differences between the biotas, ecologies and human cultures of the landmasses involved. The assertion that responses of remote island species to human predation provide realistic models for those of continental taxa is poorly founded, exaggerating the likely predation efficiency of humans colonising continents. An absence of terrestrial predators over evolutionarily significant periods, together with restricted ranges and small populations, renders island faunas uniquely vulnerable to invaders. The argument, that climate cannot explain these phenomena because previous Glacial Maxima did not cause comparable extinctions, presupposes that their local effects were at least as severe as those of the Last Glacial Maximum. This has yet to be demonstrated and at most it would indirectly support a role for anthropogenic influence, not overkill per se. Overlooked or underplayed are the influences of translocated and other invading species. Similarly, differences in the origins, technologies and traditions of colonising human societies are rarely considered. These factors strongly impact on the predation efficiency, density and range of human populations, critically affecting the outcomes of predator-prey modeling. When a fuller constellation of influences and constraints is considered it is reasonable to posit that rapid mass extinction through selective human predation may largely describe megafaunal extinctions on remote islands, but the argument is not convincing for continents. This is especially so regarding Australia. Because even the largest Australian species were prey to endemic carnivores, their responses to human predation would not have been comparable to those of oceanic island species. No kill-sites or specialized big-game hunting/butchering tools are known and, on the basis of ethnographic and archaeological data, it is probable that predation efficiency, population density and range of the first Australians were insufficient to effect rapid mass extinction. Chronologies of human arrival and the disappearance of megafauna remain poor, but the most recent estimates for human-megafaunal coexistence in Australia range from 10,000 to 43,000 years. Although human predation may have been a contributing factor in megafaunal extinctions, rapid overkill is unlikely to describe the actual mechanism in most instances. The role of human predation and its significance relative to competing factors, human and otherwise, varied considerably between landmasses, as did the speeds with which extinctions occurred. Blitzkrieg and other mono-factorial models are heuristically valuable devices, but a growing body of evidence suggests that extinction can rarely, if ever, be attributed to a single cause.

Does risk of predation influence population dynamics? Evidence from cyclic decline of snowshoe hares

Like most heavily preyed-upon animals, snowshoe hares (Lepus americanus) have to balance conflicting demands of obtaining food at a high rate and avoiding predators. Adopting foraging behaviours to minimise predation risk may also lead to a decline in condition, and hence fecundity. Predictions of three hypotheses (condition constraint hypothesis, predator-avoidance constraint hypothesis, predation-sensitive foraging (PSF) hypothesis) were tested by comparing changes in the survival and condition of snowshoe hares on four experimental areas in winter during a cyclic peak and decline (1989–1993) near Kluane Lake, Yukon, Canada, where (i) predation risk was reduced by excluding terrestrial predators (FENCE), (ii) food supply was supplemented with rabbit chow ad libitum (FOOD), (iii) these two treatments were combined (FENCE+FOOD), and (iv) an unmanipulated CONTROL was used. Different pattems of survival and changes in body mass were observed in the presence and absence of terrestrial predators. On the CONTROL area, female body mass and fecundity declined, even though sufficient winter forage was apparently available in all years. A similar decrease in body mass was observed on the FOOD treatment, but only during the third year of the population decline. In contrast, female body mass remained high throughout the decline in the absence of terrestrial predators in the FENCE+FOOD and FENCE treatments. Winter survival declined on CONTROL and FENCE areas during the first year of the population decline (1991), but remained higher on FOOD until 1992 and FENCE+FOOD until 1993. These results generally supported the PSF hypothesis where terrestrial predators were present (CONTROL and FOOD grids). Where terrestrial predators were absent (FENCE and FENCE+FOOD), the results supported the alternative condition constraint hypothesis. The evidence suggests that a cascade of sublethal behavioural and physiological effects associated with increased predation risk contribute to the population decline and delayed recovery of cyclic low-phase populations of snowshoe hares.

Ecological factors that determine distribution and abundance of the California sea lion Zalophus Californianus in the Gulf Of California

The population of the California sea lion Zulophus californianus (Lesson, 1828) in the Gulf of California during the breeding seasons of the 1980’s was estimated at 23,256 individuals, and 31,393 if census adjustments are applied. Of this total (23,256), 6.9% were adult males, 5.0% subadult males, 40.7% adult females, 23.9% juveniles, 22.7% pups (less than one year of age) and 0.8% were termed miscellaneous. Eighty-six percent of the 29 sea-lion colonies studied were on islands, while the remaining colonies occupied capes of the mainland. However, around 98.8% of the sea-lion population was counted on islands. The number of islands (available habitat) did not determine the sea-lion distribution in the gulf, but the concentration of its usual preys (sardine, anchovy, mackerel and hake) did. Eighty-two percent of the sea-lion population and its pup production took place in the northern region of the Gulf of California (from Isla San Esteban northward), which seems to be associated with the major abundance of small pelagic fish in the gulf. California sea lions tend to inhabit small- and medium-sized islands (less than 3 km in length), which amount for 80% of the sea-lion population. The probable factors that determine the selection of islands this size are: 1) the absence of terrestrial predators, 2) easier communication of breeding animals and 3) sexual selection advantage for mating individuals. The operational sex ratio varied according to island size in a negative exponential trend. More adult females were available per adult males on smaller islands, since reduced space clumped the females. This clumping effect enhances a higher male-male competition (with an evident advantage for males), but also a higher quality of territorial males for the breeding females.