Interspecific Interactions: A Case Study using the Tuatara-Fairy Prion Association

<p>Some of the key relationships in the life of an organism are interactions with individuals of other species within the community, for example, negative interactions such as predation and competition are well known to shape natural communities. Positive interactions also have well documented influences, such as intertidal seaweed canopies extending the distribution of many organisms to higher tidal heights, by reducing thermal and desiccation stresses. However, investigating interactions and measuring their significance for fitness is notoriously difficult. For example, several groups of fish are known to ‘clean’ other fish species by feeding on their ectoparasites, a mutually beneficial arrangement. However, foraging by cleaners can damage scales of their hosts and this interaction can become parasitic in times of low ectoparasite abundance. Using both field and laboratory data, I investigated factors that influenced the dynamics of an unusual vertebrate association, the cohabitation of tuatara and fairy prions in a burrow. The end goal was to contribute to the understanding of the classification of this association. The fairy prion is a seabird that comes to land only for the breeding season and the tuatara is a burrowing reptile, active primarily at night in a temperate climate. Specifically, I measured the effects that this association had on tuatara thermoregulation, and demonstrated the difficulty in applying that information to categorize a complex interaction. Investigations into the temporal and spatial habitat of the tuatara, and the degree to which this influenced thermal opportunities, revealed that mean tuatara body temperatures were always within mean environmental temperatures. Males and females did not differ in mean body temperature or effectiveness of thermoregulation. Body size did not predict body temperature or cooling rates, but heating rates were influenced, with larger animals heating faster than smaller individuals. The presence of a fairy prion in a burrow increased humidity within the burrow, and tuatara that occupied burrows containing a fairy prion were able to maintain up to 1.8°C higher body temperatures through the night during the austral summer months. Thus, burrow use behaviour and burrow selection had greater influences on tuatara body temperature than an individual’s sex or size. Experimental evidence revealed that tuatara are capable of adjusting their habitat selection behaviour in response to different humidity constraints. More time was spent outside the burrows and tuatara were more active under humid laboratory conditions. Use of the burrow by tuatara almost halved the time that fairy prions spent at the burrow with their chick, indicating that tuatara were having a negative effect on fairy prions’ use of their burrow. There was no evidence to support the fact that fairy prions were gaining any fitness benefits from their association with tuatara. Thus, we cannot call this interaction a commensalism or a mutualism. In certain instances, it may be that this interaction is best classed as a parasitism with the tuatara benefitting from burrow use and easy predation opportunities, to the detriment of the lifetime reproductive success of the fairy prion. In other instances it may simply be a case of competition for a limited resource (a burrow) with the outcome varying depending on the individuals and the circumstances involved. Being able to categorize interactions between species of high conservation value or at least to have an understanding of the costs and benefits associated with the interaction is desirable for conservation purposes, as failure to consider the ecological network within which a threatened species is embedded, may lead to counterproductive management measures. Further, these results can be used to develop future research into how climatic changes in temperature and rainfall may interact with habitat availability to influence the full range of natural outcomes of the tuatara-fairy prion association.</p>

Interspecific Interactions: A Case Study using the Tuatara-Fairy Prion Association

<p>Some of the key relationships in the life of an organism are interactions with individuals of other species within the community, for example, negative interactions such as predation and competition are well known to shape natural communities. Positive interactions also have well documented influences, such as intertidal seaweed canopies extending the distribution of many organisms to higher tidal heights, by reducing thermal and desiccation stresses. However, investigating interactions and measuring their significance for fitness is notoriously difficult. For example, several groups of fish are known to ‘clean’ other fish species by feeding on their ectoparasites, a mutually beneficial arrangement. However, foraging by cleaners can damage scales of their hosts and this interaction can become parasitic in times of low ectoparasite abundance. Using both field and laboratory data, I investigated factors that influenced the dynamics of an unusual vertebrate association, the cohabitation of tuatara and fairy prions in a burrow. The end goal was to contribute to the understanding of the classification of this association. The fairy prion is a seabird that comes to land only for the breeding season and the tuatara is a burrowing reptile, active primarily at night in a temperate climate. Specifically, I measured the effects that this association had on tuatara thermoregulation, and demonstrated the difficulty in applying that information to categorize a complex interaction. Investigations into the temporal and spatial habitat of the tuatara, and the degree to which this influenced thermal opportunities, revealed that mean tuatara body temperatures were always within mean environmental temperatures. Males and females did not differ in mean body temperature or effectiveness of thermoregulation. Body size did not predict body temperature or cooling rates, but heating rates were influenced, with larger animals heating faster than smaller individuals. The presence of a fairy prion in a burrow increased humidity within the burrow, and tuatara that occupied burrows containing a fairy prion were able to maintain up to 1.8°C higher body temperatures through the night during the austral summer months. Thus, burrow use behaviour and burrow selection had greater influences on tuatara body temperature than an individual’s sex or size. Experimental evidence revealed that tuatara are capable of adjusting their habitat selection behaviour in response to different humidity constraints. More time was spent outside the burrows and tuatara were more active under humid laboratory conditions. Use of the burrow by tuatara almost halved the time that fairy prions spent at the burrow with their chick, indicating that tuatara were having a negative effect on fairy prions’ use of their burrow. There was no evidence to support the fact that fairy prions were gaining any fitness benefits from their association with tuatara. Thus, we cannot call this interaction a commensalism or a mutualism. In certain instances, it may be that this interaction is best classed as a parasitism with the tuatara benefitting from burrow use and easy predation opportunities, to the detriment of the lifetime reproductive success of the fairy prion. In other instances it may simply be a case of competition for a limited resource (a burrow) with the outcome varying depending on the individuals and the circumstances involved. Being able to categorize interactions between species of high conservation value or at least to have an understanding of the costs and benefits associated with the interaction is desirable for conservation purposes, as failure to consider the ecological network within which a threatened species is embedded, may lead to counterproductive management measures. Further, these results can be used to develop future research into how climatic changes in temperature and rainfall may interact with habitat availability to influence the full range of natural outcomes of the tuatara-fairy prion association.</p>

Comparing post-release cover and burrow use by differentially head-started Mojave desert tortoises in southern California

The effects of indoor rearing versus the conventional method of solely outdoor head-starting on post-release cover and burrow use of juvenile Mojave desert tortoises (Gopherus agassizii), a threatened endemic species, were investigated. We found that partially indoor-reared tortoises exhibited similar post-release behaviours when compared to both same-aged, but smaller, and similar-sized, but older outdoor-reared head-started tortoises, thus increasing the success and decreasing the costs of head-starting.

Species-specific patterns of the use of burrows of Upogebia Leach, 1814 (Decapoda: Gebiidea: Upogebiidae) by the symbiotic alpheid shrimps Stenalpheops anacanthus Miya, 1997 and Athanas japonicus Kubo, 1936 (Decapoda: Caridea: Alpheidae) as revealed by laboratory quantification

Many alpheid shrimps live symbiotically on the body surface or inside the bodies of other invertebrates, while others use burrows made by other animals. The burrow symbiosis of alpheid shrimps is poorly studied in the context of ecology, probably because the cryptic infaunal nature of the relationship is hard to observe. The limited knowledge of the pattern of burrow use by alpheid shrimps leaves a gap in our understanding of their evolutionary history. We described and compared the behavior of Stenalpheops anacanthus Miya, 1997 and Athanas japonicus Kubo, 1936, two alpheid species living symbiotically in the burrows of the same host, Upogebia yokoyai Makarov, 1938. We found that both alpheid species used U. yokoyai burrows in aquaria, but their burrow use patterns were quite different. The average time taken for S. anacanthus to enter the burrow for the first time was much shorter (1 min) than that of A. japonicus (13 min). Subsequently, S. anacanthus made longer use of the burrow (80% of the observation period) than A. japonicus (49%). The tail-first exit frequency, which may indicate a sudden expulsion from the burrow by the host, was more frequent in A. japonicus (25%) than in S. anacanthus (7%). Such differences could be attributed to the nature of the symbiotic relationship, obligate in S. anacanthus but facultative in A. japonicus. Because of the diversity of symbiotic lifestyles, there is considerable potential to study the ecology and evolutionary biology of burrow-symbiotic alpheids further.

Micro-geographic variation in burrow use of Agassiz’s desert tortoises in the Sonoran Desert of California

Little has been published regarding the burrowing habits of Agassiz’s desert tortoises (Gopherus agassizii) in the Sonoran Desert of California. We monitored the interactions of tortoises with their burrows, and other tortoises, via radio-telemetry at two nearby sites between the Cottonwood and Orocopia Mountains, from 2015-2018. We examined how annual cycles of drought and non-drought years, behaviourally affected how tortoises use their burrows (i.e., burrow fidelity, cohabitation, and location), including the timing of the tortoise brumation period. Burrow locations were strongly dependent on local geology and topography, with a tendency to orientate in conformance with the general aspect of the landscape. The timing of brumation was similar to records for G. agassizii throughout their range (with a few exceptions). There was no difference in the estimated number of burrows used per 30 days between the active seasons (2017 and 2018) at the Orocopia site, despite the occurrence of drought in 2018.

Burrow use by juvenile platypuses (Ornithorhynchus anatinus) in their natal home range

We determined patterns of burrow use by juvenile platypuses (Ornithorhynchus anatinus) in their natal home range, and evaluated associations between burrows and vegetation. Between March 2015 and March 2017, we captured seven juvenile platypuses along a 3-km stretch of Badger Creek, Victoria and fitted them with radiotransmitters. We recorded the locations of animals in their burrows daily while transmitters were attached (range: 14–132 days). Juveniles used 74 different burrows, with each using 11 ± 2 burrows. Overall, 65% of burrows (48) were used once, 22% (16) were used between 2 and 9 times (moderate-use), and 13% (10) were used frequently (> 10 times). No juveniles dispersed during the monitoring period (14–132 days). Although some association was observed between burrow use and particular vegetation communities, vegetation was not a strong factor driving site selection of burrows. Use of multiple burrows may allow juveniles to avoid competition with conspecifics, reduce exposure to ectoparasites, and develop shelter-seeking behavior. Juvenile platypuses remained in their natal home range, where conditions are likely to be good because they supported recent breeding, while completing their growth and development prior to dispersal.

Social structure and reproduction of long-tailed porcupine (Trichys fasciculata)

We studied the social structure of long-tailed porcupine (Trichys fasciculata) in the tropical rainforest in Sabah, Borneo Island, Malaysia via direct observation assisted by radio-tracking and camera-trapping at burrow entrances. We identified and observed seven individuals in the study area, of which five were radio-tagged. Analysis of their burrow use, home range, and behaviour strongly suggested that five of the observed individuals formed a family group consisting of an adult male–female pair and their three offspring, two of which were born during the study period. The family members used the same burrow site almost every day, and their home ranges largely overlapped. In contrast, the other two individuals never used the burrow sites of this family group. The adult male–female pair was maintained for at least 18 months and reproduced twice during the study period. They had a litter size of one, and the inter-litter interval was estimated to be 11 months. During these two reproductions, the previous litter stayed in the natal family group as a sub-adult after the next juvenile was born. Direct paternal care, such as grooming the juvenile, was also observed. Their low reproductive potential should be considered in conservation efforts.

Environmental determinants of activity variation of an overlooked burrowing rodent: the Indian crested porcupine

A study of the activity patterns, time allocation for each activity and variations in activities due to environmental alterations are necessary for understanding the biology of any species. This study investigates the relationship of micro-habitat and environmental conditions with seasonal and temporal activities of Indian crested porcupines (ICP) around their burrows in Keoladeo National Park (KNP), India. This species is considered as a problem species, often ignoring its ecological importance as an ecosystem engineer. Of the 39 sampled burrows, 58.97%, 38.46% and 83.78% were occupied in winter, summer and monsoon, respectively. The estimated porcupine density was 3.21±1.32SD individuals/km2, accounting for a population size of 65.89±27.15SD individuals. A seasonal shift in rate of emergence was observed in monsoon and winter, when ICP emerged earlier, significantly correlating with the sunset timings. The daily activity records of adult ICP outside burrow significantly peaked in January–February when they prepare the burrows for the gestation period of 90–112 days, followed by rearing of the offspring. The temporal activity significantly reduced in the full moon nights, perhaps to avoid predators. The study affirms that environmental determinants including the timings of sunrise, sunset and lunar phase significantly affect the variations in temporal activity and burrow use patterns of ICP.