Ecology

The gobi region ecosystem has low stability because of its single species composition and simple structure (Fig. 8a). Large-scale shrub planting destroyed the original stable state (Fig. 8b) and resulted in another stable state via self-adjustment. In this process, the planted shrubs deteriorated the original ecosystem by competing for water and a chain reaction may ensue, leading to greater ecological problems. The original intention of the large-scale planting of shrubs was to maintain regional ecological balance, protect biodiversity, and fix sand, thus improving the environment (Fig. 8c). However, given the poor choice of the planting location, the expected results were not achieved. In fact, the opposite results of the original good intentions were achieved (Fig. 8d).Figure 8Diagram of different development stages of large-scale afforestation in the gobi region (a: original ground surface; b: holes dug for afforestation; c the living trees planted; d: ground surface when the trees are dead).Full size imageChina has a large expanse of arid areas, and has suffered from droughts for a long time. Land afforestation has been at the forefront of China’s policy principles, and there are government departments specializing in this field. In recent years, the Chinese Government has recommended a series of major strategies, for example, the “construction of ecological civilization” and “lucid waters and lush mountains are invaluable assets”, and also promoted greening projects, including “Three North Shelterbelt Project”, “Beijing-Tianjin Sandstorm Source Control Project”, and the “Natural Forest Protection Project”. More recently, desert greening has been conducted by people and enterprises, for example, the Ant Forest and Society of Entrepreneurs & Ecology (SEE). As a result of these projects and initiatives, China’s greening has contributed to global greening totals15,16. For afforestation, China’s policy departments have recommended the principles of “sticking to local conditions, suitable land for green, suitable trees for trees, suitable shrub for shrub, suitable grass for grass” and promoting the overall protection of “Mountain-River-Forest-Farmland-Lake-Grass-Desert system”, with particular references to desert. Their goal is to scientifically promote afforestation of the land and to clarify “where to afforest, what to afforest, how to afforest, how to manage”. However, problems arise very easily when grassroots executors are involved.The total area of the gobi region in China is approximately 56.95 × 104 km2, accounting for 13.36% of the national area, and is primarily distributed in the northwest extreme arid regions17. As mentioned above, gobi refers to a special arid landform that has a notably low water supply and is unsuitable for growing trees and shrubs. As an important natural landform, the gobi plays a key role in ecological protection; hence, its reference as “black vegetation”. However, there is a lack of understanding of the gobi, and it is often regarded as an area that needs to be greened or reformed. However, gobi, as an extremely arid region, is a fragile ecosystem. Once the gravel on the gobi surface is destroyed, it could lead to a series of ecological and environmental problems. Therefore, afforestation in arid areas is both a scientific and technical issue which must be conducted according to different regional characteristics, rather than by blindly planting trees in unsuitable areas. This study aims to attract more attention from the government forestry department and implementation personnel involved in afforestation activities so as to revise relevant policies. In response to the findings of this study, we have several recommendations: (1) it is necessary to popularize the understanding of scientific greening within the general public; (2) scientific understanding of the gobi needs to be increased, and awareness must be raised to promote its protection; (3) afforestation projects and management must be scientifically and systematically improved to ensure long-term effectiveness, and; (4) restoration and protection measures should be taken immediately in the gobi regions that have been afforested or destroyed.One of the most important causes of all these problems is the implementation of national policies on subsidies for greening and planting trees in desert areas. According to our survey, personnel who specifically plant trees and engage in afforestation are businessmen, farmers, or others, with most of them being businessmen from abroad, and only a few being local people. All the personnel are more concerned about the subsidies than greening and planting trees itself. According to the policy, they will receive majority of the subsidy if the planted trees live for three years, irrespective of whether the trees survive after that. Therefore, to guarantee the survival of the planted trees for three years, they even use water tankers to carry water to the trees from a great distance. However, after three years, the people stop watering the trees planted in the Gobi region, thereby leading to the death of trees after a few years as they cannot survive only on natural precipitation and groundwater. In pursuit of maximum profits, these businessmen will pursue larger areas for planting trees, which will cause further damage to the ecological environment in the Gobi region. Based on the current situation, we propose the following suggestions: (1) Trees that are planted must be monitored over a long time period, which will greatly reduce the short-term profit motive of the people engaged in planting trees. (2) We must plan greening and planting trees according to local conditions, respecting the laws of nature. Not all areas should be greened; moreover, we should not plant trees, especially in the gobi region, where planting trees can possibly destroy the gobi ecological environment, which is a very fragile desert ecosystem. (4) Personnel responsible for the destruction of the gobi ecological environment by unscientific greening and planting of trees must be obligated to restore the surface conditions of the gobi to prevent the aggravation of wind erosion and desertification, which will increase their awareness of environmental protection and receive punishment for environmental damage. More

A Psammodromus algirus lizard in Spain, where wildfires can confer long-lasting relief from parasites. Credit: Philippe Clement/Nature Picture Library

Ecology
13 July 2021
Destructive fires serve as pest control for lizards

Mediterranean lizards in burnt areas are less likely to be afflicted by mites than their neighbours in unburnt woodlands.

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Occasional wildfires can help lizards to keep a clean house: the blazes cleanse natural areas of mites that can infest the reptiles’ skin.High-intensity fires in Mediterranean shrublands and woodlands renew vegetation, shoo away seed eaters and keep tree diseases in check. Lola Álvarez-Ruiz at the Desertification Research Centre in Valencia, Spain, and her colleagues were curious to know whether the flames could also be beneficial to animals.Between 2016 and 2018, the researchers sampled Psammodromus algirus, a species of ground-dwelling lizard, in eight burnt and adjacent unburnt areas in Spain. They then counted either how many mites were attached to the creatures’ skin or how many raised scales the lizards had — an indication of previous infection with the parasite.Lizards that lived in unburnt areas were four times more likely to carry mites than were those in recently scorched environments, and were also more likely to have raised scales. The results suggest that there was a lower incidence of parasitism even several years after a fire had occurred.

Proc. R. Soc. B (2021)

Ecology More

Oceanographic context of the sampling locationAll Trichodesmium colonies used in this study were collected from the same phytoplankton net which sampled a surface-ocean Southern Caribbean Sea community (Fig. 1a). At the sampling station the phosphate concentration was low (0.13 μM at 100 m) as is typical in an oligotrophic environment, while the surface dissolved iron concentration was relatively high (2.02 nM at 100 m), consistent with coastal or atmospheric inputs being mobilized in this region (Fig. 1a). By far the most abundant Trichodesmium species at this location was an uncharacterized Trichodesmium thiebautii species, as determined by Trichodesmium-specific metagenome-assembled-genome recruiting (see Table S1).Thirty individual colonies of mixed morphology were separated by hand-picking, immediately examined, and photographed by fluorescent microscopy (385 excitation, >420 nm emission), then frozen individually for particle characterization and metaproteomic analysis (Fig. S1). All colonies used in this study presented as healthy with reddish-orange pigmentation and well-defined shape. When the particles were present they auto-fluoresced in the visual light range, appearing as yellow, red, or blue dots. In general, the particles were concentrated in the center of puff-type colonies, though they were also present in tufts but in smaller numbers. Strikingly, colonies either had many such particles or none at all. Based on prior experimental evidence demonstrating that Trichodesmium colonies can capture mineral particles and access iron from them [14,15,16, 21], we hypothesized that these particles were terrestrially derived minerals (Fig. 1c–h). Therefore, we embarked to understand the morphological heterogeneity by characterizing the particles and the colony’s molecular response to them.Mineralogical characterization of the colony-associated particlesTo find out whether these natural colonies of Trichodesmium had captured iron-rich mineral particles, we performed synchrotron-based micro-X-ray fluorescence (μ-XRF) element mapping of representative colonies with the observed particle associations. Prior evidence of Trichodesmium–particle associations has been based mainly on experimental “feeding” of dust to cultured or captured colonies [15, 16, 20, 22,23,24,25], and it was therefore important to establish these specific Trichodesmium–particle relationships, which developed in nature. We examined one tuft- and two puff-type colonies, all of which had particles associated with them. The element maps were consistent with the hypothesis that there were mineral particles enriched in iron (Fe), copper (Cu), zinc (Zn), titanium/barium (Ti/Ba, which cannot be distinguished by this method), manganese (Mn) and cobalt (Co), though the concentrations approached the limit of detection for the latter two elements (Fig. 2, Figs. S2 and S3). Iron concentrations were particularly high in the particles. Micro-X-ray absorption near-edge structure (μ-XANES) spectra for iron were collected on six particles—three each from the two puffs (Fig. 2 and Fig. S4). The particles contained mineral-bound iron with average oxidation states of 2.6, 2.7, two of oxidation state 2.9, and two of oxidation state 3.0 (Table S2, Fig. S5). While the mineralogy of these particles could not be definitively resolved using μ-XANES, the structure of the absorption edge and post-edge region provided insight into broad mineral groups. Both Fe(III) (oxy/hydro)oxides and mixed-valence iron-bearing minerals consistent with iron silicates were present, suggesting heterogeneous mineral character. While we could not positively identify the silicate mineral phases based on XANES, the spectroscopic similarity of some samples to iron-smectite and the geologic context suggest iron-bearing clays were present (Fig. S5). In this geographic region, iron oxides and clays could be sourced from atmospheric dust deposition, which is common in this region [27, 28] and/or from riverine sources such as the Orinoco and/or Amazon rivers [29, 30].Fig. 2: μ-XRF-based element maps of a Trichodesmium tuft (left) and puff (right) colony (beamsize 3 ×3 μm).White/gray contours, based on the sulfur panel, which is indicative of biomass, have been provided (white = high [S] threshold, gray = lower [S] threshold). The color scale is the same for each image, with the maximum concentration for each element indicated in parentheses; iron is displayed using two scales. Iron oxidation states were determined via μ XANES for three particles in the puff colony, and these are annotated in yellow. The corresponding XANES spectra are shown in Fig. S4 and tabulated data in Table S2.Full size imageThese colony-associated mineral particles likely serve as a simultaneous source of nutritional (Fe, Ni, Co, Mn) and toxic (Cu) metals to the colonies. The elemental composition of the particles is similar to a recent characterization of Trichodesmium-particle associations in the South Atlantic [30]. Release of metals from the particles likely vary over time, with copper, nickel, zinc, and cobalt continually leaching and iron leaching initially, then re-adsorbing back onto particles unless organic chelates assist in solubilization [31].Proteome composition is altered by particle presenceTo understand the impact of the particles on colony diversity and function, we performed comparative metaproteomic analysis of the individual Trichodesmium colonies and their microbiota. Seven puffs without particles, 14 puffs with particles, and 4 tufts with particles were analyzed by a new single-colony metaproteomic method. This approach allowed for the first time the molecular profiles of heterogeneous Trichodesmium colonies to be examined individually. Compared to bulk population-level metaproteomes from this location, which achieved deeper resolution of low-abundance proteins by integrating biomass from 50 to 100 colonies (4478 proteins identified) [32], proteome coverage for the low-biomass single colonies was lower yet sufficient for characterizing colony function (2078 proteins identified, Fig. S6) [32]. In total, 1591 Trichodesmium and 487 epibiont proteins were identified across the 25 single-colony metaproteomes versus 2944 Trichodesmium and 1534 epibiont proteins across triplicate population-level metaproteomes (Tables S3 and S4). Phylogenetic exclusivity was checked such that peptides used to identify epibiont proteins were not present in the Trichodesmium genome (Table S5 and Fig. S7) [33, 34].Trichodesmium’s epibiont community plays crucial roles in colony health and physiology, and together the single-colony proteomes demonstrated a diverse and functionally active microbiome associated with the colonies (Fig. 1b and Fig. S8). The proteomic analysis generally reflected the more abundant, “core” members of the epibiont community as was expected given their low-biomass proportion relative to Trichodesmium cells. Many commonly identified epibiont groups were present including Alphaproteobacteria, Microscilla, and non-Trichodesmium cyanobacteria [12, 35, 36]. In general, epibiont abundance was unaffected by particle presence, with one exception: Firmicute proteins were more abundant in tufts and puffs with particles, suggesting enhanced, possibly anaerobic, metabolism. Greater differences were identified between the puff and tuft morphologies, independent of particle presence and consistent with prior characterizations finding that puffs and tufts harbor distinct epibiont communities [12]. Specifically, eukaryotic proteins were more abundant in puffs compared to tufts. These proteins likely represent copepods due to sequence similarity to the model organism Calanus finmarchicus, and this result is consistent with observed associations between copepods and puffs at this location (Fig. S8B). Notably, proteins from the PVC superphylum, particularly an uncharacterized eukaryote pathogen species related to Chlamydia, were also more abundant in puffs. Eukaryotes are often observed in association with Trichodesmium colonies, but are not always identified due to differences in sampling protocols that could wash them away [12], as well as due to biases in analytical methods, for instance in studies with a focus on bacterial 16S or metagenomic analyses. Overall, the differences in the epibiont community were small, suggesting that these do not explain the observed morphological heterogeneity. We therefore turn our attention to describing how the particles impacted the proteome of Trichodesmium specifically.Mineral presence was associated with significant differences in the Trichodesmium proteome. In total, 131 proteins were differently abundant in puffs with particles versus without particles (p  More

Soil diversity, taxonomic classification and binning of BGCsNonpareil analysis estimated an abundance-weighted coverage of 85.3% for the 44.4 Gb used in the long-read assembly. To achieve 95% and 99% coverage, respectively, 250 Gb and 1.6 Tb of sequencing were predicted to be necessary. Alpha diversity was estimated at Nd = 21.6. Contigs were binned using CONCOCT, MaxBin2 and MetaBAT2, consensus bins were generated using metaWRAP refine and classified using GTDB-Tk. This yielded 114 bacterial bins with CheckM completeness  > 50% and contamination  More

If an endpoint of continued circulation (endemicity rather than eradication) seems likely, this still leaves us with questions about the range of outbreak sizes, their intensity and seasonality. Surprisingly, some basic epidemiological parameters for predicting these dynamical features are still uncertain. For example, R0, the reproductive number, which captures the infectiousness of the pathogen, is typically measured from the growth of the epidemic and is harder to estimate once non-pharmaceutical interventions (NPIs) are in place. Similarly, changes to R0 for evolved SARS- CoV-2 variants are difficult to ascertain given simultaneous changes to behaviour and interventions. It is not yet clear whether there is an evolutionary limit to strain infectiousness. To date, structural changes to the SARS-CoV-2 spike furin cleavage site7 as well as enhanced binding of the receptor binding domain to the human ACE2 receptor8 have been associated with enhanced transmissibility in variant strains, but in the longer term, transmission increases may saturate and viral evolution may modulate other aspects of disease transmission including host susceptibility. Nevertheless, any present or future changes to R0 will affect long-term epidemic dynamics, including the intensity of outbreaks and the age-structure of infections.The transmission of many respiratory pathogens varies seasonally, driven either by climatic factors or seasonal changes in behaviour such as schooling. The role of climate in driving transmission of SARS-CoV-2 is currently unclear: high susceptibility during the early pandemic likely limited any climate effect9, and statistical analyses of the climate-SARS-CoV-2 link have been confounded by trends in the data and regional differences in reporting and control measures. This has not been helped by the relatively short case time series (that is, just over a year’s worth of data) compared to typical climate–disease studies that look for climate links over many seasons. An alternative line of evidence comes from the four endemic coronaviruses, which exhibit seasonal wintertime outbreaks. It is possible that SARS-CoV-2 will follow suit. Disentangling the climate drivers of SARS-CoV-2 will become easier over time as both longer time series are available, and susceptibility declines9.A further question is the extent to which SARS-CoV-2 endemic dynamics will be affected by interactions with other circulating pathogens, including the endemic coronaviruses. Both modelling and laboratory work implies a degree of cross-immunity between coronaviruses10,11,12. The NPIs put in place to limit the spread of SARS-CoV-2 have also limited the circulation of many other pathogens, such that infection interactions have not been observed in current case trajectories13. However, as NPIs are relaxed, signatures of cross-species interactions will likely become increasingly visible.Beyond cross-immunity with other pathogens, the longitudinal trajectory of immunity, as depicted in Fig. 1, will play a crucial role in determining SARS-CoV-2 endemic dynamics14. For immunizing infections, susceptibility is driven by birth rates, and infections may be concentrated in younger age groups. For infections with waning immunity or antigenic evolution, susceptibility is driven by the rate at which immunity wanes or the rate the pathogen evolves as well as characteristics of secondary infections. The disease dynamics of pathogens with high rates of antigenic evolution are particularly hard to predict: evolved strains may have variable transmission rates and manifest variable immune responses. An analogy can be made with influenza, where the size and intensity of the seasonal influenza peak is typically very difficult to forecast15.The future course of SARS-CoV-2 remains uncertain. The next few months to a year represents a critical time where we will begin to develop an understanding of key parameters, such as the strength and duration of vaccinal and natural immunity, the seasonality of transmission and the possible interaction of SARS-CoV-2 with other circulating pathogens. In combination, these parameters will allow improved prediction of both long-term SARS-CoV-2 epidemic dynamics, as well as the likelihood of elimination and eradication. An area of particular focus will be the rate of antigenic evolution and the extent to which vaccines remain protective against evolved strains. In all scenarios, rapid and equitable distribution of vaccines presents the greatest hope for minimizing future severe outbreaks. More

Climate change mitigation and adaptation, including through nature-based measures, are urgently needed. Now mapping and valuation of global vegetated coastal and marine blue carbon ecosystems shows how interlinked countries are when dealing with climate change.Towards the end of the eighteenth century, Adam Smith’s famous The Wealth of Nations highlighted the role of the different aspects comprising a country’s wealth, including its natural resources or natural capital. Today, the ‘inclusive wealth’ concept, encompassing the different forms of capital which constitute the wealth of a country (natural, manufactured, human and social capital), expands this idea6. Blue carbon ecosystems are valuable natural capital assets. One way to value their worth is using the social cost of carbon (SCC), which is estimated through complex models that include physical and economic variables. The SCC values the ‘marginal’ damaging effects of an additional ton of CO2 emissions in the atmosphere, or the benefit of a removed ton of CO2 emissions, for society7. Greenhouse gas emissions to the atmosphere are a global problem; therefore, the SCC is a global estimate. Based on the assumption that climate change effects are felt differently in different countries, in 2018, Ricke et al.8 elaborated a new model to calculate these damages at the national level through the country-specific SCC (CSCC). To value blue carbon assets, the extent of each ecosystem, and how much carbon it sequesters and stores, have to be known. The areal extent is multiplied by the carbon burial rate of the blue carbon ecosystems in a specific geographical region — the precise species of mangroves, saltmarshes and seagrasses also plays a role in terms of carbon sequestration and storage rate — and by the chosen SCC. Uncertainty surrounding these factors is high because of the current lack of data on the precise extent of worldwide vegetated coastal and marine ecosystems, as well as their carbon sequestration and storage rates, and because of the uncertainty surrounding some of the chosen physical and economic variables used in the models estimating the SCC9. More

We collected and analysed hourly GPS data from Antarctic fur seal pups tracked from birth until moulting in order to investigate the drivers of movement patterns and activity levels during this critical life stage. We found that pup movement was characterised by a star-like pattern, with individuals repeatedly returning to a central location of low activity after bouts of directed exploration. The HMM showed that the probability of such active movement was highest during the day and was mainly influenced by breeding season, colony of birth, and age. Our findings provide new insights into the movement patterns of pinnipeds prior to nutritional independence and highlight the importance of the life-history stage and the neonatal environment on behaviour.Movement in fur seal pupsA recent study of movement in Antarctic fur seal pups found evidence for sex-specific differences in habitat use prior to nutritional independence and the onset of overt sexual size dimorphism. Specifically, male pups were found to exhibit more risk prone behaviour with increasing age, traveling further at sea and spending more time in exposed beach habitats26. While this study highlighted the importance of an intrinsic factor, sex, on neonatal movement, the contributions of other factors, both extrinsic and intrinsic, remained largely unexplored. Our HMM incorporated multiple environmental and individual-based variables including the time of day, air temperature, wind speed, age, body condition, and sex. Rather than focusing on animals from a single colony, our study used tracking data from two breeding colonies with contrasting population density and terrain, while replication across two consecutive breeding seasons also allowed us to account for inter-annual variation in food availability.Our hourly GPS data revealed a distinct pattern of terrestrial pup movement that has not been reported in previous studies. Specifically, we documented a star-like pattern characterised by directed movement away from and subsequent return to a location of low activity. This appears to be a genuine behavioural pattern rather than an artefact of our temporal scale of sampling, as GPS locations collected every five minutes from a subset of individuals revealed a very similar picture (Supplementary Fig. S4). Star-like movement patterns are typified by central place foragers, which make round trips between a central location and a foraging patch37. However, as fur seal pups are entirely reliant on their mothers for food until they moult, repeated movements away from a central location are unlikely to be related to resource acquisition. Instead, our results appear to be indicative of bouts of exploration within a defined radius around a suckling location, which would imply that Antarctic fur seal pups are ‘central place explorers’.We would expect central place exploration in fur seal pups to be adaptive given that it entails energetic costs37 and might even make it more difficult for pups to be located by their mothers when they return from foraging trips38. We can envisage a number of possible explanations for this behaviour. First, high levels of activity may facilitate the development of the muscle mass necessary for future foraging success. Second, movement both within and beyond the confines of the beach where a pup is born may increase the scope for social interactions, which might be important for future mating success18. Third, a transition from beach habitats to the tussock grass offers increased protection against harsh weather conditions and may reduce the risk of a pup either being crushed by a territorial male or predated.While all tracked individuals displayed this pattern of central place exploration, the distance travelled during bouts of exploration differed depending on the colony of birth. On average, pups born at FWB travelled shorter distances and stayed closer to their colony of birth, whereas SSB pups moved farther and in a larger variety of directions. Given that SSB pups tend to transition into the tussock grass later in life (see discussion below), one explanation for this difference may be that mother–pup pairs need to travel further inland to find an appropriate, unoccupied suckling location.Results of the HMMWe used an HMM framework to infer the discrete behavioural states underlying pup movement and the probability of switching between these states given certain environmental and individual covariates. This integrated approach to decompose behavioural patterns has been applied across a wide range of species and habitats and has emerged as a powerful tool for animal movement modelling5. Our model uncovered a strong influence of year, with the probability of occupying the active state being higher in the first breeding season (2019), particularly for FWB pups. One possible explanation for this pattern could be that inter-annual differences in movement are adaptive. The first breeding season in our study had among the lowest breeding female numbers, pup birth weights, and foraging trip durations on record28, reflecting poor environmental conditions and low prey abundance39. In 2019, local densities at both colonies were correspondingly below average28. Given a greater risk of predation at low density28, pups might increase their activity to avoid harassment, pecking injuries, and predation by generalist seabirds such as southern and northern giant petrels40. Alternatively, higher levels of activity could be a consequence of increased stress hormone levels. As mothers spent more time at sea foraging in 201928, pups were subjected to longer periods of food deprivation. Such extended bouts of starvation in pinniped pups have been associated with an increase in glucocorticoids41, which are known to increase activity levels in some species42. Understanding the interrelationships among prolonged fasting, glucocorticoids levels, and activity in fur seal pups may help to shed further light on individual responses to environmental challenges.Another clear extrinsic determinant was the time of day, with activity levels peaking just before solar noon. This observation is in line with a previous study of Galápagos fur seal pups18, but otherwise very little is known in general about diurnal patterns of activity among fur seals while ashore. Daily meter-resolution location data from densely packed territory holding Antarctic fur seal males reveal negligible movements from day to day29, implying that these animals remain more or less stationary. By contrast, telemetry studies of adult females have reported associations between nocturnal foraging behaviour and diel variation in the time of arrival and departure from the breeding colony43. Consequently, it is unclear to what extent our results can be extrapolated across the life history, especially given the likelihood of an ontogenetic shift in times of peak activity as pups transition from being reliant on milk to nutritional independence.The HMM also revealed an increase in pup activity with age, but only for pups born at FWB. One explanation for this colony-specific difference could be that FWB pups are able to express their full behavioural repertoire throughout the course of ontogeny, becoming more active as they grow, whereas pups born on SSB are constrained by the high density of conspecifics. In particular, pups that traverse tightly packed harems on SSB run a higher risk of being crushed by a territorial male or bitten by a breeding female21,22. Alternatively, we recently found that FWB pups are more likely to be predated by generalist seabirds28. This might translate into an increase of predator-avoidance activity as pups mature, which would help to explain why activity no longer increases after around 40 days of age, when the majority of individuals have transitioned to the more sheltered tussock grass.We found that pups from FWB tended to move into the tussock grass earlier than pups from SSB and spent proportionally more time in the tussock grass than in their colony of birth. While this earlier shift toward residing mainly in the tussock grass could simply be a consequence of increased activity, it might also be adaptive for FWB pups to move inland as quickly as possible given the higher risk of predation at low density28. In other words, pups may move into the more sheltered tussock grass earlier in life and remain there for longer periods of time in order to avoid predatory seabirds. However, differences in the topography of the two colonies might also influence the timing of this transition, as a steep gully separates the beach at SSB from the tussock grass, while FWB offers a more gradual transition between the two habitats. To disentangle the effects of density and topography would require a larger study embracing a greater diversity of breeding colonies.Contrary to our initial expectations, the HMM found little to no effect of air temperature or wind speed on pup activity. This is surprising given that the pups in our study lacked the water-repellent fur of adults and were thus poorly protected from the elements23. Reduced activity35 and huddling behaviour44 have been documented in pinniped neonates as effective thermoregulatory behaviours to withstand the respectively hottest and coldest daily temperatures, so we originally anticipated a reduction in pup activity under marginal weather conditions. However, large variation in temperature during the course of this study was not observed on Bird Island (2019 mean temperature = 3.7 °C ± s.d. 1.3; 2020 mean temperature = 3.9 °C ± s.d. 1.4). Consequently, behavioural adjustments in activity for effective thermoregulation may not have been necessary in the context of our study. Alternatively, other climatic variables that we could not account for, such as precipitation or humidity, may have a disproportionate influence on activity levels. Future studies involving the direct observation of focal individuals under specific climatic conditions would help to address this question.The HMM also showed that pup activity levels were largely unaffected by body condition. This was unexpected because Antarctic fur seal pups rely on their mother’s milk for nutrition before moulting and must tolerate bouts of starvation lasting up to 11 days while their mothers forage at sea19. As a result, pup growth is known to decline with prolonged maternal absence45, implying that fewer resources should be available for movement. Taken at face value, the lack of a relationship between body condition and movement may suggest that the short-term benefits of high activity, such as muscle mass development and increased social interaction, may outweigh the costs associated with diverting resources from growth. This would be in line with a previous study that found that Galápagos fur seal pups maintained high activity levels throughout bouts of starvation18. However, it is also possible that an effect of body condition could not be detected in our study because our model assumed that condition was constant between successive measurements, whereas in practice it will vary to some extent from day to day.Despite a number of studies having shown that sex-specific differences in activity, habitat use, foraging, and diving behaviour are established early in life in several pinniped species13,14,15,16,17,46, including Antarctic fur seals26, our HMM did not uncover any obvious sex differences in activity. This is probably a consequence of the timeframe of our study. Jones et al.26, for example, only detected sex-specific differences in habitat use in Antarctic fur seal pups greater than 41 days old. Given that we focused on the time window from birth until moulting at around 60 days of age, the results of these two studies are consistent and lend support to the notion that sex-specific movement patterns take several weeks to become established.Results of the post-hoc analysisThe post-hoc analysis showed that pups were significantly less active when their mothers were ashore, suggesting that pup activity is correlated to some extent with maternal foraging behaviour. This association is most likely a reflection of the utmost importance of milk consumption for pup survival and development. A mother may spend as little as 24 h and on average only two days ashore during each nursing bout43, so pups must maximise nutrient update during this time. Moreover, adult female fur seals frequently display aggressive behaviour towards foreign pups21, potentially limiting a pup’s opportunity for social interactions when the mother is present18. It is important to note, however, that although significant, the effect size of the correlation between pup activity and maternal presence was fairly small. This suggests that pups may not remain with their mothers for the entire maternal attendance period, but rather alternate between nursing and bouts of activity.We also found that pups that died tended to be considerably less active. In our dataset, cause of death was assigned to all but one pup as either starvation (n = 5) or predation (n = 6), two factors that are difficult to untangle given that smaller, weaker (i.e. starving) pups may be more likely to be predated. It is possible that the reduced activity of pups that died could be related to poor body condition. While this would appear to contradict the lack of an overall association between activity and condition in the HMM, it is possible that activity may decline only after body condition falls below a critical threshold18, an effect we may not have captured due to the small number (n = 13) and early occurrence (median = 15 days) of mortalities in our dataset. Alternatively, causality could flow in the other direction, with less active pups being more likely to be predated. This would be more in line with our HMM results as well as with the hypothesis that increased activity is related to predator-avoidance behaviour.Strengths, limitations, and future directionsRecent advancements in bio-logging technology and analytical methods have made tracking studies of small, juvenile individuals ethically feasible, cost effective, and analytically approachable. In this study, we have taken advantage of these advancements to implement one of the first in-depth analyses of the movement and activity patterns of Antarctic fur seal pups prior to moulting. We were able to uniquely incorporate individual, ecological, and environmental variation into our analyses by collecting time-series biometric data for all tagged individuals, which were sampled at two breeding colonies across two subsequent breeding seasons. Finally, we were able to tease apart how these intrinsic and extrinsic factors may influence movement by inferring behavioural states using a HMM.An important limitation of our study, however, is our inability to establish causal relationships between hypothesised explanatory factors and activity. While this is an ever-present challenge when working with wild populations, future studies may consider pairing GPS tracking data with detailed behavioural observations of the focal individuals. This would provide a behavioural context for movement patterns and possibly allow for a more nuanced interpretation of the underlying behavioural states. A higher GPS sampling rate might also facilitate the resolution of finer-scale states. While this was not possible in the current study due to the limited battery capabilities of our tags, as technologies continue to improve future studies may not need to sacrifice sampling resolution for study duration. Finally, it would be interesting in the future to consider GPS tracking both mothers and pups to better understand the relationship between maternal attendance behaviour and pup activity. This approach might also shed light on how mothers find their offspring after returning ashore from foraging trips. More

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