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Are the ghosts of nature’s past haunting ecology today?
Abstract
Humans have decimated populations of large-bodied consumers and their functions in most of the world's ecosystems. It is less clear how human activities have affected the diversity of habitats these consumers occupy. Rebounding populations of some predators after conservation provides an opportunity to begin to investigate this question. Recent research shows that following long-term protection, sea otters along the northeast Pacific coast have expanded into estuarine marshes and seagrasses, and alligators on the southeast US coast have expanded into saltwater ecosystems, habitats presently thought beyond their niche space. There is also evidence that seals have expanded into subtropical climates, mountain lions into grasslands, orangutans into disturbed forests and wolves into coastal marine ecosystems. Historical records, surveys of protected areas and patterns of animals moving into habitats that were former hunting hotspots indicate that - rather than occupying them for the first time - many of these animals are in fact recolonizing ecosystems. Recognizing that many large consumers naturally live and thrive across a greater diversity of ecosystems has implications for setting historical baselines for predator diversity within specific habitats, enhancing the resilience of newly colonized ecosystems and for plans to recover endangered species, as a greater range of habitats is available for large consumers as refugia from climate-induced threats.
... After decades of legal protection and conservation efforts, some of the world's most depleted and endangered wildlife populations are recovering and re-colonizing regions from which they had once been extirpated (Halley and Rosell 2002, Heide-Jørgensen et al. 2007, Ripple and Beschta 2007, Buxton et al. 2014, Silliman et al. 2018. Although encouraging, this recovery process is sometimes associated with new conservation and management challenges. ...
... The single habitat predictor used for the earlier analysis was a relatively simple classification of substrate type (rocky, sandy, mixed), but researchers have reported that sea otter abundance and foraging success are affected by a broader array of environmental features including coastal bathymetry (Thometz et al. 2016), kelp canopy cover (Nicholson et al. 2018), benthic substrate complexity and composition (Stewart et al. 2015, and ocean productivity (Davis et al. 2019). We now understand that estuarine systems may represent important sea otter habitat, distinct from soft-sediment areas of the outer coast (Hughes et al. 2013, Silliman et al. 2018. Recent innovations in remote sensing, substrate characterization using multi-beam sonar, and analysis using geographic information systems (GIS) have made data available for all these habitat features in coastal California waters, thereby enabling a more comprehensive examination of habitat predictors of carrying capacity. ...
... Infaunal invertebrate species (e.g., clams, marine worms) and epifaunal species (e.g., crabs, fish, sharks, rays; Hechinger et al. 2011) can occur at high densities. Sea otters can use any estuarine waters having sufficient tidal exchange to support marine invertebrate prey assemblages; recent evidence suggests that estuarine systems may potentially support higher densities of sea otters than comparable soft-sediment areas along the outer coast (Silliman et al. 2018). ...
The recovery of large carnivore species from over‐exploitation can have socioecological effects; thus, reliable estimates of potential abundance and distribution represent a valuable tool for developing management objectives and recovery criteria. For sea otters (Enhydra lutris), as with many apex predators, equilibrium abundance is not constant across space but rather varies as a function of local habitat quality and resource dynamics, thereby complicating the extrapolation of carrying capacity (K) from one location to another. To overcome this challenge, we developed a state‐space model of density‐dependent population dynamics in southern sea otters (E. l. nereis), in which K is estimated as a continuously varying function of a suite of physical, biotic, and oceanographic variables, all described at fine spatial scales. We used a theta‐logistic process model that included environmental stochasticity and allowed for density‐independent mortality associated with shark bites. We used Bayesian methods to fit the model to time series of survey data, augmented by auxiliary data on cause of death in stranded otters. Our model results showed that the expected density at K for a given area can be predicted based on local bathymetry (depth and distance from shore), benthic substrate composition (rocky vs. soft sediments), presence of kelp canopy, net primary productivity, and whether or not the area is inside an estuary. In addition to density‐dependent reductions in growth, increased levels of shark‐bite mortality over the last decade have also acted to limit population expansion. We used the functional relationships between habitat variables and equilibrium density to project estimated values of K for the entire historical range of southern sea otters in California, USA, accounting for spatial variation in habitat quality. Our results suggest that California could eventually support 17,226 otters (95% CrI = 9,739–30,087). We also used the fitted model to compute candidate values of optimal sustainable population abundance (OSP) for all of California and for regions within California. We employed a simulation‐based approach to determine the abundance associated with the maximum net productivity level (MNPL) and propose that the upper quartile of the distribution of MNPL estimates (accounting for parameter uncertainty) represents an appropriate threshold value for OSP. Based on this analysis, we suggest a candidate value for OSP (for all of California) of 10,236, which represents 59.4% of projected K. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society. We use a spatially explicit population model to explore the functional relationships between biotic and abiotic habitat variables and carrying capacity (K) of southern sea otters in California, USA, 1983–2018. We estimate that California could support 17,226 sea otters at K, with local densities varying from <1 to >10 otters/km2 based on habitat quality, and we suggest a candidate value for optimal sustainable population abundance of 10,236.
... Because the initial recovering population occurred in kelp forests along the open coast throughout the sea otter range, foundational studies on the ecology of sea otters have focused on this habitat (Lowry & Pearse, 1973;Estes & Palmisano, 1974;Simenstad, Estes & Kenyon, 1978). A similar of baseline knowledge on alternate habitat types has been seen for other top predators around the world, which rather than occupying seemingly unique habitats for the first time, are in fact reoccupying historical habitat (Silliman et al., 2018). As a result of historical accident (i.e., the location of the surviving population), sea otters in California have become closely associated with kelp forests in the minds of both the public and scientists. ...
... In contrast, sea otters in Elkhorn Slough utilize inland estuarine habitats extensively. Over the past two decades, the Elkhorn Slough population has increased rapidly to more than 100 animals and has only recently shown signs of reaching equilibrium (Silliman et al., 2018). The initiation of the period of rapid growth in Elkhorn Slough can partly be attributed to the addition of rehabilitated sea otters from the Monterey Bay Aquarium, specifically to 14 females that survived for >1 year post release and were among the first animals to reproduce in the Slough (Mayer et al., 2019). ...
... Estuaries such as Elkhorn Slough are home to diverse and abundant invertebrate communities (Wasson et al., 2002), and sea otter prey such as clams, crabs and worms can recruit and grow rapidly (Dataset S3). The high productivity of prey resources has supported decades of high foraging success of the dense sea otter population (Hughes et al., 2013;Silliman et al., 2018). ...
Recovering species are often limited to much smaller areas than they historically occupied. Conservation planning for the recovering species is often based on this limited range, which may simply be an artifact of where the surviving population persisted. Southern sea otters (Enhydra lutris nereis) were hunted nearly to extinction but recovered from a small remnant population on a remote stretch of the California outer coast, where most of their recovery has occurred. However, studies of recently-recolonized estuaries have revealed that estuaries can provide southern sea otters with high quality habitats featuring shallow waters, high production and ample food, limited predators, and protected haul-out opportunities. Moreover, sea otters can have strong effects on estuarine ecosystems, fostering seagrass resilience through their consumption of invertebrate prey. Using a combination of literature reviews, population modeling, and prey surveys we explored the former estuarine habitats outside the current southern sea otter range to determine if these estuarine habitats can support healthy sea otter populations. We found the majority of studies and conservation efforts have focused on populations in exposed, rocky coastal habitats. Yet historical evidence indicates that sea otters were also formerly ubiquitous in estuaries. Our habitat-specific population growth model for California's largest estuary-San Francisco Bay-determined that it alone can support about 6,600 sea otters, more than double the 2018 California population. Prey surveys in estuaries currently with (Elkhorn Slough and Morro Bay) and without (San Francisco Bay and Drakes Estero) sea otters indicated that the availability of prey, especially crabs, is sufficient to support healthy sea otter populations. Combining historical evidence with our results, we show that conservation practitioners could consider former estuarine habitats as targets for sea otter and ecosystem restoration. This study reveals the importance of understanding how recovering species interact with all the ecosystems they historically occupied, both for improved conservation of the recovering species and for successful restoration of ecosystem functions and processes.
... When high trophic-level species recover, they may have substantial effects on the trophically downgraded systems to which they return. As predators become reestablished, they may occupy new habitats, or broaden their diet, leading to increased diversity in niche space (i.e., Silliman et al., 2018). Recovering predator populations can also induce ecological changes that exert feedback on prey or habitat availability, further diversifying or expanding the predator's niche space (Estes, Jameson, & Rhode, 1982;Tinker, Bentall, & Estes, 2008). ...
... Both mean prey size and energy intake rates were lower in long-occupied areas than in recently occupied areas. These niche space differences among sites with varying occupation times likely reflect sea otter behavioural responses to variation in prey availability-a legacy of the effects that sea otters exert on benthic prey communities as they recover (i.e., Estes, Riedman, Staedler, Tinker, & Lyon, 2003;Tinker, Bentall et al., 2008 Although niche space has not been thoroughly examined in sea otters (but see Silliman et al., 2018), sea otter diets have been well studied. In British Columbia (Breen, Carson, Foster, & Stewart, 1982;Hessing-Lewis et al., 2017;Honka, 2014), Washington (Laidre & Jameson, 2006;Hale et al., in press), California (Estes et al., 1982(Estes et al., , 2003Tinker, Doak et al., 2008;Tinker et al., 2012), and Alaska (Hoyt, 2015;Kvitek, Oliver, DeGange, & Anderson, 1992;Weizman, 2013), sea otter diets have been found to differ among recently and longoccupied areas. ...
... Understanding how prey selection and the range of habitats used by sea otters vary over the course of recovery has important implications for sea otter conservation and affects our understanding of the recovery process in a predator that has traditionally been studied in a limited context (Silliman et al., 2018 Estes & Palmisano, 1974;Estes & Duggins, 1995). Although research has focused on the role of sea otters in hard substrate areas, they use soft substrate areas as well, at both recent-and long-occupied sites (Kvitek, Fukayama, Anderson, & Grimm, 1988;Kvitek et al., 1992;Weizman, 2013) and particularly in stormy weather (Garshelis & Garshelis, 1984). ...
Predators exert strong effects on ecological communities, particularly when they re‐occupy areas after decades of extirpation. Within species, such effects can vary over time and by sex and cascade across trophic levels. We used a space‐for‐time substitution to make foraging observations of sea otters (Enhydra lutris) across a gradient of reoccupation time (1–30 years), and nonmetric multidimensional scaling (nMDS) analysis to ask whether (a) sea otter niche space varies as a function of occupation time and (b) whether niche space varies by sex. We found that niche space varied among areas of different occupation times. Dietary niches at short occupation times were dominated by urchins (Mesocentrotus and Strongylocentrotus spp; >60% of diets) in open habitats at 10–40 m depths. At longer occupation times, niches were dominated by small clams (Veneroida; >30% diet), mussels (Mytilus spp; >20% diet), and crab (Decapoda; >10% diet) in shallow (<10 m) kelp habitats. Diet diversity was lowest (H′ = 1.46) but energy rich (~37 kcal/min) at the earliest occupied area and highest, but energy poor (H′ = 2.63, ~9 kcal/min) at the longest occupied area. A similar transition occurred through time at a recently occupied area. We found that niche space also differed between sexes, with bachelor males consuming large clams (>60%), and urchins (~25%) from deep waters (>40 m), and females and territorial males consuming smaller, varied prey from shallow waters (<10 m). Bachelor male diets were less diverse (H′ = 2.21) but more energy rich (~27 kcal/min) than territorial males (H′ = 2.54, ~13 kcal/min) and females (H′ = 2.74, ~11 kcal/min). Given recovering predators require adequate food and space, and the ecological interactions they elicit, we emphasize the importance of investigating niche space over the duration of recovery and considering sex‐based differences in these interactions.
... Megafauna are often perceived to use coastal areas as marginal habitats only occasionally or intermittently (5), making it difficult for scientists and/or the public to connect them with certain nearshore systems (except for some groups, such as sea turtles and seals, that are notable exceptions because they make more predictable and conspicuous visits to coastal habitats). Moreover, coastal ecosystems are often among the world's most densely populated and affected by humans (6), with the role of megafauna in coastal ecosystems unrecognized partly because their abundance, behavior, and habitats have been severely altered by human activities in what is a catastrophic example of shifting baselines (7)(8)(9). ...
... Nonetheless, emerging research is revealing that many coastal ecosystems provide essential habitats for megafaunal species (10)(11)(12). For example, after successful population recovery, sea otters have expanded into salt marshes; river otters and alligators have expanded into coastal wetlands; and wolves, bears, and pumas have been sighted foraging along shorelines (9). Vegetated coastal wetlands, in particular, provide intermittent but important foraging and/or breeding habitats for at least 174 species of megafauna globally, accounting for over 13% of all extant marine megafauna (12). ...
To fulfill sustainable development goals, many countries are expanding efforts to conserve ecologically and societally critical coastal ecosystems. Although megafauna profoundly affect the functioning of ecosystems, they are neglected as a key component in the conservation scheme for coastal ecosystems in many geographic contexts. We reveal a rich diversity of extant megafauna associated with all major types of coastal ecosystems in China, including 218 species of mammals, birds, reptiles, cephalopods, and fish across terrestrial and marine environments. However, 44% of these species are globally threatened, and 78% have not yet been assessed in China for extinction risk. More worrisome, 73% of these megafauna have not been designated as nationally protected species, and <10% of their most important habitats are protected. Filling this wide "megafauna gap" in China and globally would be a leading step as humanity strives to thrive with coastal ecosystems.
... ecological refuges), and a shy fauna was promoted by the selective removal of bolder individuals (Gaynor, 2019;Martínez-Abraín et al., 2019). That fauna is now recovering exploratory behaviours, moving out of their ecological refuges, showing less fear to human presence, and getting closer to urban areas (Silliman et al., 2018;Martínez-Abraín et al., 2019, 2021b. ...
... These vultures nest on pine trees growing directly in the cliffs facing the sea, instead of nesting on the holm oak (Quercus ilex) forest patches in the island sierras, as they usually do in mainland Spain. The choice of this nesting microhabitat has been considered for decades an idiosyncratic trait that deserves preservation, rather than the ghost of severe past human persecution (Silliman et al., 2018;Martínez-Abraín et al., 2019), as we think it is the case. The reinforcement of the remaining population with individuals from outside the Balearic Islands carried out by conservation practitioners during the last few decades may have brought back a broader behavioural variability to the population that hopefully will be able to move soon out of the cliffs and grow at a faster rate in the large pine and holm oaks forests in the island. ...
Past human persecution of wildlife has acted as a major selection agent shaping many animal features including behaviour. A major component of behaviour with diverse consequences for conservation is the shyness/boldness continuum. Shyer individuals are often geographically restricted, less prone to wander out of their ecological refuges but, on the contrary, less likely to experience human-induced mortality and lead to human-wildlife conflict. In this essay we discuss how the success of translocations may interact both positively and negatively with animal personalities, based on several case studies of re-introductions and reinforcements involving remnant mammal and bird populations. Although shyness may be inconvenient to conservationists when dealing with raptor translocations in which eventual dispersal may be a desired trait in the long run, a trade-off may emerge between boldness and prevention of human-wildlife conflict when dealing with large carnivores. Some other trade-offs may also occur, such as that between boldness and desired philopatry at the initial stage of re-introductions.
... It is, however, unlikely that current geographic ranges reflect the full set of suitable climates that a species would be able to inhabit under current climates and landscapes, but without human interference (Martínez-Freiría et al., 2016;Nüchel et al., 2018;Silliman et al., 2018). Should there be favorable environmental conditions in areas where species have been extirpated due to nonclimatic processes, only a subset of their suitable environments, that is, realized climatic niches (Soberón & Peterson, 2005), will be occupied in geographic space (Peterson et al., 2018). ...
... In that case, parts of the species' niches are said to be unfilled (sensu Guisan et al., 2014) as a consequence of reductions in their geographical distributions (Martínez-Freiría et al., 2016). This sub-representation of geographical distributions limits our understanding of the environmental constraints of numerous species (Martínez-Freiría et al., 2016;Nüchel et al., 2018;Silliman et al., 2018;Walder et al., 2021) and may bias conservation strategies based exclusively on current distributional patterns Rodrigues et al., 2019). Moreover, in cases where the unfilling of niches was caused by the extirpation of populations in optimal environments, remaining populations may now occupy regions of marginal suitability and be at higher risk from subsequent stressors (Bocherens et al., 2015;Kuemmerle et al., 2012;Nüchel et al., 2018). ...
Humans have reshaped the distribution of biodiversity across the globe, extirpating species from regions otherwise suitable and restricting populations to a subset of their original ranges. Here, we ask if anthropogenic range contractions since the Late Pleistocene led to an under‐representation of the realized niches for megafauna, an emblematic group of taxa often targeted for restoration actions. Using reconstructions of past geographic distributions (i.e., natural ranges) for 146 extant terrestrial large‐bodied (>44kg) mammals, we estimate their climatic niches as if they had retained their original distributions and evaluate their observed niche dynamics. We found that range contractions led to a sizeable under‐representation of their realized niches (i.e., niche unfilling). For 29 species, more than 10% of the environmental space once seen in their natural ranges has been lost due to anthropogenic activity, with at least 12 species undergoing reductions of more than 50% of their realized niches. Eighteen species main now be confined to low‐suitability locations, where fitness and abundance are likely diminished; we consider these taxa climatic refugees. For those species, conservation strategies supported by current ranges risk being misguided if current, suboptimal habitats are considered baseline for future restoration actions. Because most climate‐based biodiversity forecasts rely exclusively on current occurrence records, we went on to test the effect of neglecting historical information on estimates of species’ potential distribution – as a proxy of sensitivity to climate change. We found that niche unfilling driven by past range contraction leads to an overestimation of sensitivity to future climatic change, resulting in 50% higher rates of global extinction, and underestimating the potential for megafauna conservation and restoration under future climate change. In conclusion, range contractions since the Late Pleistocene have also left imprints on megafauna realized climatic niches. Therefore, niche truncation driven by defaunation can directly affect climate and habitat‐based conservation strategies.
... Apex predators play a key role in top-down regulation of ecosystems, often with cascading effects when an apex predator leaves or enters a system (Estes et al. 2011). In the past century, many apex predator populations crashed (Prugh et al. 2009;Estes et al. 2011), but some populations have recovered recently; for example large carnivores in Europe and wolves (Canis lupus), sea otters (Enhydra lutris), and alligators (Alligator mississippiensis) in different parts of the USA (Chapron et al. 2014;Ripple et al. 2014;Silliman et al. 2018). Following the ban of organochloride pesticides and reduced persecution, the populations of apex raptors, such as Peregrine Falcons (Falco peregrinus) and Ospreys (Pandion Haliaeetus), have also recovered (Ratcliffe 2003;Poole 2019). ...
... Following the ban of organochloride pesticides and reduced persecution, the populations of apex raptors, such as Peregrine Falcons (Falco peregrinus) and Ospreys (Pandion Haliaeetus), have also recovered (Ratcliffe 2003;Poole 2019). The growing populations are spreading into new areas, often re-colonizing areas they once inhabited (Silliman et al. 2018). This return of apex predators is a complex issue. ...
Many apex predator populations are recolonizing old areas and dispersing to new ones, with potential consequences for their prey species and for livestock. An increasing population of the White-tailed Eagle (Haliaeetus albicilla) has settled north of the Arctic Circle in northern Finland, mainly at two big water reservoirs but also in areas with mainly terrestrial habitat. We examined nesting habitat preferences and prey use of White-tailed Eagles in this environment, where reindeer husbandry is a traditional livelihood and concerns are rising that the growing White-tailed Eagle population poses a threat to reindeer calves. Lakes, peat bogs, and marshlands were preferred habitats in the nesting territories. Fish constituted 64.3% of the identified prey items, with birds accounting for 28.5% and mammals 7.2%. The nesting territory habitat within a 10 km radius and the latitude influenced the prey composition at both the group and species level. The occurrence of reindeer calves as prey increased with latitude but was not associated with any habitat. Knowledge of the diet and territory preferences can be used to predict future dispersal and local prey use of this species. Nesting White-tailed Eagles do not seem to pose a threat to traditional reindeer herding, but further research is needed regarding non-breeding sub-adults and whether the White-tailed Eagles actually kill reindeer calves or simply exploit their carcasses.
... The notable and relatively recent expansions of American alligators and sea otters into salt marshes, along with a recent review study that found salt marshes are home to at least a few more megafauna (e.g., crocodiles, harbor seals) (Sievers et al., 2019), indicate that there are likely more megafauna species that utilize salt marshes than is represented in this global metaanalysis of top-down effects in salt marshes (He and Silliman, 2016). In southeastern United States salt marshes, for example, researchers found that in marine protected areas, densities of the American alligator (Alligator mississippiensis) were higher than in comparable freshwater systems (Nifong and Silliman, 2017;Silliman et al., 2018). Alligators not only fed on marine animals in salt marshes, but more than 50% of the gut contents were marine animals, such as blue crabs (Callinectes sapidus), shrimp, and string rays (Nifong and Silliman, 2013). ...
... Sea otter, harbor seal, wild horse, and alligator densities had a higher relative abundance in salt marshes than in other established habitats (Figure 2). We predict that salt marshes, because of their high primary and secondary productivity, could be generally attractive ecosystems for megafauna in search of food and/or nursery grounds and that the diversity of megafauna using marshes will continue to increase as megafauna recover from overexploitation, as occurred with sea otters and alligators (Silliman et al., 2018). Additionally, the large difference between the diversity of animals within consumer effects studies and those who use salt marshes globally indicates that, while there are several megafauna species, such as alligators and hogs, whose impacts have been documented, there are likely animals impacting salt marshes whose effects have not been quantified. ...
Megafauna shape ecosystems globally through trophic interactions, ecology of fear, and ecosystem engineering. Highly productive salt marshes at the interface of terrestrial and marine systems have the potential to support megafauna species, but a recent global meta-analysis of consumer-plant interactions in marshes found few studies investigated impacts of wild megafauna. We conducted a literature review to document the variety of megafauna in salt marshes and found that 34 species utilize salt marshes, including sharks, manatees, pinnipeds, crocodilians, sea otters, hippos, and large terrestrial animals, such as lions, bears and water buffalo. The use of salt marsh habitats by a variety of megafauna may have implications for both the conservation of these large consumers and for the resilience of coastal wetlands through stabilizing feedbacks on plant ecosystems. Future studies should quantify the occurrence and impacts of megafauna in salt marshes, and how their conservation can help restore these valuable ecosystems.
... While hailed as a conservation success story, the return of sea otters exemplifies the challenge of a predator returning to its native range, which raises ecological, conservation, and management questions (Roman et al. 2015, Silliman et al. 2018. In particular, the recovery of sea otter populations resulted in conflicts with human interests for shellfish resources (Carswell et al. 2015). ...
... As predator populations continue to recover worldwide, ecologists, conservation biologists, managers, and other stakeholders are likely to face new questions regarding the management of these species (Silliman et al. 2018). In preparation for, or in response to, recovering predator populations, it will be important to re-examine the spatial context of current management frameworks and their ability to effectively manage spatially heterogeneous populations (Mahoney et al. 2018). ...
To better understand the spatial context of population dynamics of sea otters (Enhydra lutris) in Southeast Alaska (SEAK), we investigated the spatial and temporal patterns of subsistence sea otter harvest and assessed the effect of harvest on population growth. U.S. federal law permits subsistence harvest of sea otters and sale of clothing and handicrafts made by coastal Alaska Natives. Hunters are required to self-report these harvests along with information on date, location, age class, and sex. Using harvest data collected from 1988 to 2015, we developed a spatially explicit, age-structured, density-dependent population simulation model to explore the potential impacts of harvest on sea otter population dynamics. We examined patterns of harvest and simulation model results at two spatial scales: the SEAK stock and three smaller subregions that vary in sea otter occupation time and carrying capacity: Sitka Sound, Keku Strait, and the Maurelle Islands. Annual sea otter harvest in SEAK increased from 55 animals in 1988 to a reported maximum of 1449 animals in 2013. Estimated mean annual harvest rate was 2.8% at the SEAK stock scale, but ranged from 0% to 39.3% across the three focal subregions described above. Across all sub-regions (n = 55), annual sea otter harvest rate was strongly influenced by time since recolonization, sea otter population density, and proximity to communities with sea otter hunters. The simulation model predicted population trends and per capita harvest rates similar to those estimated from aerial survey data, providing a reasonable approximation of population dynamics. Results of the simulation model suggested that current harvest levels can reduce population size at both the SEAK and subregional scales. Variation in harvest impacts was a function of subregion-specific factors, including time since recolonization and population status with respect to carrying capacity. We found that subsistence harvest and its population effects were scale-and location-dependent, indicating that higher spatial and temporal resolution of sea otter population and hunting data could help address emerging sea otter management and conservation concerns in this region.
... Vision may aid pandas when discriminating conspecifics at a distance, detecting salient black-white fur coloration with a distinct black eye mask, as well as mutant fur color phenotypes, where brown pandas are reported frequently in the Qinling Mountains, Shaanxi Province (Editorial 1991) and a wild albino panda was recently dicovered in the Wolong Nature Reserve, Sichuan Province (Chang 2019). Vision may also assist pandas to discern sympatric species (Li et al. 2020) and 'ghosts of recent predators past' (Silliman et al. 2018), particularly those that could pose a threat to them or their vulnerable altricial neonates (Schaller et al. 1985 A c c e p t e d M a n u s c r i p t which five are competitors for food, dens (Lai et al. 2020) Better understanding the ability of pandas to discriminate humans from other animals visually is important because this has likely been advantageous during their recent evolution, due to encroachment on panda habitat by villagers, agriculture, and livestock. This severely impacted their habitat and caused a catastrophic decline in their numbers in the latter part of the 20 th Century, so much so that concerted conservation efforts in China since 1989 have been necessary to recover giant pandas from the brink of extinction. ...
The role that visual discriminative ability plays among giant pandas in social communication and individual discrimination has received less attention than olfactory and auditory modalities. Here, we used an eye-tracker technology to investigate pupil fixation patterns for eight captive male giant pandas Ailuropoda melanoleuca. We paired images (N = 26) of conspecifics against: 1) sympatric predators (gray wolves, tigers), and non-threatening sympatric species (golden pheasant, golden snub-nosed monkey, takin, red panda), 2) conspecifics with atypical fur coloration (albino, brown), and 3) zookeepers/non-zookeepers wearing either work uniform or plain clothing. For each session, we tracked the panda’s pupil movements and measured pupil first fixation point (FFP), fixation latency, total fixation count (TFC) and duration (TFD) of attention to each image. Overall, pandas exhibited similar attention (FFPs and TFCs) to images of predators and non-threatening sympatric species. Images of golden pheasant, snub-nosed monkey and tiger received less attention (TFD) than images of conspecifics, whereas images of takin and red panda received more attention, suggesting a greater alertness to habitat or food competitors than to potential predators. Pandas’ TFCs were greater for images of black-white conspecifics than for albino or brown phenotypes, implying that familiar color elicited more interest. Pandas reacted differently to images of men vs women. For images of women only, pandas gave more attention (TFC) to familiar combinations (uniformed zookeepers and plain-clothed non-zookeepers), consistent with the familiarity hypothesis. That pandas can use visual perception to discriminate intra-specifically and inter-specifically, including details of human appearance, has applications for panda conservation and captive husbandry.
... space that prevents human-wildlife conflict within the context of normal human activity (Dennehy et al. 2021). However, the converse process is also true, with nocturnal mammals that have been persecuted over centuries becoming more diurnal once human persecution is halted, a process that is currently ongoing in most of Europe and North America (Sterba 2012;Martínez-Abraín and Oro 2018;Silliman et al. 2018;Martínez-Abraín et al. 2019a;Cimatti et al. 2021). For example, Eurasian otters (Lutra lutra), seldom seen foraging during the day in the recent past in European countries, can now be studied by direct diurnal observation of individuals in the wild at relatively short distances in human-made reservoirs (Llinares et al. 2019). ...
Wolves have been the archetype of wildlife persecution by humans for centuries all over the world, and still are heavily persecuted in some regions. Facultative diurnal/nocturnal wild mammals are known to become more nocturnal when persecuted. Conversely, little is known regarding the possibility of wolves becoming more diurnal if not persecuted. We took advantage of a 9-year natural experiment of restricted human access to a restored coal mine debris dump to study the daily activity patterns of wolves under conditions of infrequent human presence. Results were compared with a paired control site with frequent human use. Circadian wolf activity was monitored using camera traps (3 years in human-restricted site; 2 years in control). Additionally, data from two GPS–GSM-collared wolves monitored in a second control site were also analyzed. In our control sites, wolves were nearly inactive during daylight hours. In contrast, in the human-restricted site wolves extended their activity toward noon, with a daily activity peak between 10:00 and 12:00, and showed some activity throughout the entire circadian 2-h interval cycle considered. Wolves clearly had higher diurnality in the human-restricted area with 78% greater incidence of capture with remote cameras during the day than in the control site. We suggest that the shift toward increased diurnality was related to the loss of fear of humans. Evidence in support of this hypothesis comes from flight initiation distance (FID) data. Wolves showed relatively short FIDs when faced with a human observer (range 70–183 m) in broad daylight at the human-restricted site, but were so afraid of humans in the control site that we were unable to conduct FID trials there. Based on these results, we suggest that wolves may increase their diurnality in those European countries with currently increasing movement of human populations from rural to urban areas and that do not conduct lethal control of wolves. This would represent a historical landmark for a species that has been persecuted for many centuries. However, such behavioral shifts could bring new human–wolf conflicts that would require new policies.
... However, extensive conservation efforts and reintroduction projects along with the ban of problematic pesticides have resulted in a recent recovery of some apex predator populations, including wolves in northern Europe and the US, and alligators and sea otters in the US. These are spreading back to areas where they once occurred, as well as into novel environments (Chapron et al. 2014;Ripple et al. 2014;Silliman et al. 2018). While beneficial for the biodiversity and functionality of the ecosystems, the return of apex predators might cause conflicts with humans because they are seen as competitors for resources, or as a threat to livestock (Nyhus 2016;Cammen et al. 2019;Salvatori et al. 2020). ...
Apex predators regulate ecosystems through top-down processes. In the last century many predator populations crashed due to anthropogenic impacts, but recently some have recovered and are re-colonizing old areas, as well as expanding to new suitable habitats. Rapid loss or return of apex predators can destabilize ecosystems and cause consequences for their prey species as well as for livestock. In the Baltic Sea area, the white-tailed eagle (Haliaeetus albicilla) was virtually absent due to persecution and pollutants during the mid-20th century. The rapid growth of the eagle population from the 1980s onward initiated by extensive conservation efforts has not only brought the species back from the brink of extinction, but also caused growing predation pressure on its prey species, in particular the common eider (Somateria mollissima), which is the major prey of the eagles in the Åland islands and especially in the outer archipelago. In Lapland in northern Finland, where husbandry of semi-domestic reindeer is a traditional livelihood, concerns are rising that the expanding white-tailed eagle population poses a threat to reindeer calves. As top predators, the white-tailed eagles are sensitive to bioaccumulating hazardous substances. Despite the decreased levels of pollutants, the Baltic Sea is still the world’s most heavily polluted sea, while mercury levels in the major water bodies in Lapland, two artificial water reservoirs, are higher than in the Baltic.
For successful conservation of both the white-tailed eagle and its prey species research is needed regarding the diet of the eagles and the mechanisms shaping the diet. This system also provides an opportunity to study the predator-prey dynamics following the rapid return of an apex predator to a system from where it has been virtually absent. In this thesis I cover (i) the prey use and nesting habitat choice of white-tailed eagles nesting in the Finnish coast and Lapland, (ii) the connections between the prey use and the nesting habitat, (iii) the use of reindeer calves as prey, (iv) the association between nesting white-tailed eagles and the spatiotemporal population trends of the common eider, and (v) the consequences of prey use and nesting site choice on the mercury burden in white-tailed eagle nestlings in Lapland.
I found that the prey use of white-tailed eagles changed in time in the archipelago, and that it both in the archipelago and in the inland was influenced by the habitat in the nesting territories, which reflects the occurrence of prey species. In the inland, the white-tailed eagles preferred territories with higher proportions of lakes, peatbogs, and marshlands, which coincides with the higher occurrence of their preferred food source, fish. In the archipelago the main prey of the white-tailed eagles was common eider, which population in the Baltic has declined rapidly since a peak in 1997. The spatiotemporal changes in the core of the eider population distribution were influenced by the proximity of nesting white-tailed eagles. The eiders declined most in the outer archipelago and on unforested islands in the proximity of eagle nest. On the contrary, the population increased in the inner archipelago in areas with eagle nests. Finally, the prey use and nesting habitats influenced the eagles themselves. Elevated mercury burdens in white-tailed eagle nestlings in Lapland were linked with a diet on high trophic-level species and especially pike, the most important prey species in the area, as well as the proximity to a point source; the artificial reservoir of Porttipahta.
As flexible opportunists, the white-tailed eagles should not be food-deprived even though some prey species would decline. Likewise, the prey species should not be over-exploited, as the eagles use alternative prey species when a species decline. Population-level eagle-induced shifts has moved the core of the eider population towards safer nesting environments in the inner archipelago. However, the very rapid decrease of eiders calls for close monitoring and conservation efforts of the species.
As top predators, the white-tailed eagles are prone to accumulation of pollutants and are as such excellent sentinel species for environmental pollution. However, consequently they are also vulnerable and thus, even though the population today is viable, a continuum of the thorough monitoring of the white-tailed eagles is important.
The ecosystem resilience is today severely challenged by anthropogenic impacts. Returning apex predators can improve the states of the ecosystems by e.g. preventing over-grazing, controlling the growth of prey populations and restricting invasive mesopredators. Successful co-existence with humans requires a general acceptance of the predators which only can be gained through cooperation and involvement of stakeholders and inhabitants that are affected by the matter.
... Ecological legacy effects refer to preexisting anthropogenically induced conditions in ecosystem structure and the environment that continue to affect processes in the present day (Silliman et al., 2018). Temporal scales of legacy effects range from decades to hundreds or even thousands of years, and spatial scales encompass whole ecosystems, catchments, or biogenic regions. ...
Abstract Aotearoa New Zealand is the last major landmass settled by people, and therefore provides a recent record of ecological legacy effects in the coastal zone. Large‐scale land clearances of forests accelerated over the last century, affecting the concentration of suspended sediments, light environment, and nutrient composition on rocky reefs, and consequently the distribution, abundance, and composition of algal forests. The environmental effects were compounded in many places by overfishing and long‐term declines of large predatory species, often leading to proliferation and extensive grazing by sea urchins. In this study, we examine these processes in three biogeographic regions that have been differentially affected by ecological legacy effects. The study was based on the depth‐specific associations between sea urchins (Evechinus chloroticus) and the common kelp (Ecklonia radiata) from multiple sites within each region, some of which were sampled over two decades within no‐take marine reserves and in actively fished areas. Satellite‐derived estimates of water‐column properties were used as proxies for the relative effects of coastal sedimentation on kelp forest habitats. We then used an information‐theoretic framework to assess the relative factor weightings of marine reserve effects on urchin density, total suspended solids (TSS), and regional urchin density on the depth‐specific density of Ecklonia radiata. The fishing effects were significant within and outside of reserves in the northern and central regions, but the effect sizes were by far strongest in the northern region. In the central region characterized by extensive land clearance and forestry combined with high coastal retention of water, the concentration of TSS had a major influence on the depth distribution of kelp, confining it to shallow water (
... Our concepts of the habitat affinities and constraints of species can be influenced by historic and prehistoric anthropogenic legacies (Silliman et al., 2018) and by sampling biases (Britnell et al., 2021). This can stymie empirical understandings of ecological change, even leading to efforts to eradicate species perceived as non-native in seemingly novel habitats (e.g., List et al., 2007;Martin et al., 2017). ...
American black bears are considered dependent on high‐elevation forests or other montane habitats in the drylands of western North America. Black bear sign, including that of cubs, was observed throughout the summers of 2015, 2016, and 2018 along a perennial desert river in the Sonoran Desert of Arizona. We analyzed the contents of 21 black bear scats, collected from May to October of 2016 and 2018. Apache cicada nymphs (Diceroprocta apache) were the dominant food item, occurring in 90% of scats and comprising an average of 59% of scat contents. In the process of excavating these nymphs, bears created large areas of turned‐over soil, a form of ecosystem engineering with potential implications for soils, vegetation, and fluvial geomorphology. Given that species distributions are shaped by physiological and ecological contexts, as well as anthropogenic legacies, it is possible that black bears once occurred more commonly in desert riparian systems prior to widespread agricultural development, hunting, and dewatering. Although more research is necessary, we suggest that desert riparian systems may be an alternative habitat for black bears. Better understanding the diet and habitat breadth of American black bears is important in the context of increasing landscape fragmentation and militarization in the U.S.‐Mexican borderlands. American black bears are generally considered forest habitat dependent species. However, we report on black bears in a riparian system in the Sonoran Desert, with an unusual diet dominated by cicada nymphs. Our results suggest that much remains unknown about the ecologies of even a well‐studied species like American black bears.
... As such, predators can serve as "sentinels" to reflect ecosystem decline [12]. Fortunately, predators have also demonstrated the potential to recolonize formerly occupied habitat [13]. In a sim-Sustainability 2021, 13, 12832 2 of 22 ilar way, predators can potentially serve as indicators of ecosystem recovery, making them ideal candidates to reflect restoration success. ...
Coastal habitats are declining worldwide, which has impacted economically important fisheries , especially in the Indian River Lagoon, Florida. As a result, extensive intertidal oyster reef and living shoreline restoration projects have been implemented. Restoration can also theoretically benefit predator populations, but this relationship is understudied. Here, the impact of habitat restoration on juvenile predatory fish (i.e., sportfish) populations (abundance) and communities (species richness, diversity, and assemblage) was assessed prior to and following oyster reef restoration and living shoreline stabilization for up to three years, and incorporated the influence of 17 environmental predictor variables. Juvenile sportfish abundance and richness (n = 11) were variable over time but collectively higher on restored oyster reefs compared to controls, and similar between control and stabilized shorelines. Sportfish abundance was best described by a combination of biotic features of the site (e.g., reef height and benthic substrate cover), prey abundance, decreasing distance to the nearest ocean inlet and dissolved oxygen. Results suggest future restoration site selection should emphasize adequate dissolved oxygen (~6 mg/L), oyster densities above 50/m 2 and reef height above 55 mm, and minimum shoreline vegetation coverage of 50% to support macrofaunal prey and subsequently attract sportfish. These findings can help natural resource managers better use habitat restoration as a tool for enhancing fish populations in the future.
... Coastal ecosystems are increasingly affected by abiotic and biotic forcings like drought, habitat fragmentation, and species invasions that simultaneously apply pressure to the positive interactions that drive resilience. Our experiments, surveys, and mathematical models suggest that southeastern U.S. marsh resilience will be especially vulnerable to these effects without intense feral hog hunting or the reintroduction/rewilding of natural predators 85 . Large invasive consumers like hogs represent management challenges in increasingly novel humaninfluenced ecosystems 86 . ...
Invasive consumers can cause extensive ecological damage to native communities but effects on ecosystem resilience are less understood. Here, we use drone surveys, manipulative experiments, and mathematical models to show how feral hogs reduce resilience in southeastern US salt marshes by dismantling an essential marsh cordgrass-ribbed mussel mutualism. Mussels usually double plant growth and enhance marsh resilience to extreme drought but, when hogs invade, switch from being essential for plant survival to a liability; hogs selectively forage in mussel-rich areas leading to a 50% reduction in plant biomass and slower post-drought recovery rate. Hogs increase habitat fragmentation across landscapes by maintaining large, disturbed areas through trampling of cordgrass during targeted mussel consumption. Experiments and climate-disturbance recovery models show trampling alone slows marsh recovery by 3x while focused mussel predation creates marshes that may never recover from large-scale disturbances without hog eradication. Our work highlights that an invasive consumer can reshape ecosystems not just via competition and predation, but by disrupting key, positive species interactions that underlie resilience to climatic disturbances.
... Obligate kelp beds habitat Substantial predator protection and increased food in seagrasses and salt marshes (Silliman et al., 2018) Failure to conserve across full range of suitable habitats; incorrect assumptions used in species distribution models ...
Taxonomic and geographic biases in ecological research are widely recognised. In addition, information bias within a species can impact our understanding of their biology. This can lead to an underestimation of potential intra- or inter-population level variation and plasticity, and incomplete inferences about species response curves across environmental gradients. The consequences of these ‘species stereotypes’ are misestimation of the potential niche and narrow, potentially biased, views of habitat and diet preferences. For example, species may be characterised as ecologically static, or a habitat, diet, or prey ‘specialist’. Several factors can contribute to the formation of a ‘stereotype’, including a focus on extant populations, or a subset of them, that only partially represent the full historical distribution of a species, and an emphasis on species interactions derived from a small number of potential communities. Such species stereotypes are likely widespread and impact on many taxa. These misconceptions can have knock-on effects for conservation programmes and lead to ineffective or harmful conservation interventions such as actively managing species in marginal habitats, not identifying key threats and incorrect predictions of vulnerability to environmental change. Recognising biases is vital to addressing these potential problems and providing accurate information for conservation programmes. Biases can be identified by evaluating historical distributions, translocations within historical distributions, developing mechanistic distribution models and assessing traditional ecological knowledge. We suggest that explicit assessment of biases and potential stereotypes are included in red listing or species assessments, biodiversity action plans, and protected area network design and evaluation.
... To date it remains unclear if the positive effects of sea otters to seagrass, or kelp forests (Estes and Duggins 1995), outweigh their negative effects on these fisheries (Larson et al. 2013, Carswell et al. 2015, Hoyt 2015 in southeast Alaska. As predator populations continue to recover, an understanding of their effects in multiple ecosystems, and across multiple spatial scales will be essential for their successful conservation and management (Roman et al. 2015, Silliman et al. 2018). Our study directly addressed these questions and found that sea otters may not generate a trophic cascade in seagrass ecosystems characterized by low dissolved nitrate levels, and low epiphyte and epifauna biomass. ...
The presence and strength of trophic cascades can be a function of the local abiotic environment and relative abundance of key species. The reintroduction and expansion of sea otters Enhydra lutris, a known keystone species in kelp ecosystems, in southeast Alaska provides a rare natural experiment to test the generality of a apex-predator-seagrass trophic cascades across a broad spatial scale. We conducted an in-depth sea-grass community survey at 21 sites spanning ~100 km with variable sea otter presence to test for patterns of alternating abundance and direct relationships between species indicative of trophic cascades. Our analysis revealed some of the trophic relationships predicted by the apex predator-seagrass trophic cascades theory, including a strong negative relationship between sea otters and crabs and many of the expected relationships between nitrate, seagrass, epiphytes and epifauna. Other expected relationships within a trophic cascade, however, were not supported-including no relationship between crabs and epifauna, a critical link in the trophic cascade. Given the lack of evidence for all hypothesized direct relationships, we conclude that a sea otter mediated trophic cascade may not be present in southeast Alaska and could be due to local scale factors including the spatial heterogeneity, low resource availability and non-linear food chains in southeast Alaska seagrass communities. However, correlation analyses suggest further interactions among biological and environmental variables in southeast Alaska seagrass communities, including a positive correlation between sea otters and seagrass biomass. These results suggest that the effects of recovering apex-predator populations may not be generalizable across regions and spatial scales, highlighting a need for local assessment on the ecology and management of these populations.
... Historical and archaeological evidence indicates that southern sea otters were once abundant in California estuaries (Ogden 1941, Jones et al. 2011, which can provide relatively protected habitats compared to higher-mortality coastal zones , Nicholson et al. 2018. Furthermore, estuarine habitats will likely play a critical role in supporting future southern sea otter population growth and range expansion in California (Silliman et al. 2018, Hughes et al. 2019. ...
Protective legislation and management have led to an increase in California’s sea otter Enhydra lutris nereis population. While sea otter recovery has been linked to ecosystem benefits, sea otter predation may negatively affect commercially valuable species. Understanding the potential influence of sea otters is of particular importance as their range expands into estuaries that function as nurseries for commercially valuable species like Dungeness crab Metacarcinus magister. We consider how sea otter predation has affected the abundance and size of juvenile Dungeness crab in Elkhorn Slough, California, USA, and analyzed cancrid crab abundance and size across 4 California estuaries with and without sea otters to understand how biotic and abiotic factors contribute to observed variation in crab size and abundance. We compared trends in southern sea otters relative to Dungeness crab landings in California to assess whether increasing sea otter abundance have negatively impacted landings. In Elkhorn Slough, juvenile Dungeness crab abundance and size have declined since 2012, coinciding with sea otter population growth. However, the impact of sea otters on juvenile Dungeness crab size was habitat-specific and only significant in unvegetated habitat. Across estuaries, we found that cancrid crab abundance and size were negatively associated with sea otter presence. While abiotic factors varied among estuaries, these factors explained little of the observed variation in crab abundance or size. Although we found evidence that sea otters can have localized effects on cancrid crab populations within estuaries, we found no evidence that southern sea otters, at recent population sizes, have negatively impacted Dungeness crab landings in California from 2000−2014.
... Many animal populations that were formerly secluded in remote areas with little human disturbance (ecological refuges) are leaving those suboptimal habitats (now legally protected as nature or national parks) at an increasing rate. They are progressively re-colonizing other habitats due to the lack of direct human persecution associated to the human depopulation of rural areas (Morandini et al., 2017;Silliman et al., 2018;. The reduction in direct human persecution does not entail a complete absence of threats to wildlife. ...
The depopulation of rural areas by humans had marked ecological consequences on wildlife in southern Europe, which became evident fifteen years ago. Shrub and tree encroachment, and the expansion of forest birds and of the formerly persecuted mammalian ungulates and carnivores, were highlighted as the major consequences of the rural exodus in Italy. In this essay, we provide a more integrative view, and show that this process also explains other ecological phenomena that are usually treated independently. After reviewing the consequences of the rural exodus that has been affecting a large part of Spain during the last six decades, we suggest that this set should also include the movement of shy-selected predators and big game out of their former ecological refuges, as well as the increased frequencies of individuals with bolder-behaviours in recovering populations. We develop a conceptual model linking the increasing approach of wildlife to anthropogenic habitats and human depopulation of rural areas. These links are created by the likely increasing difficulty to survive and reproduce in recovering (high-predation) areas due to mesopredator release, and the loss of fear to humans. We acknowledge that the recovery of formerly persecuted wildlife in depopulated landscapes has been helped by conservation policies, but we suggest that policies alone cannot explain the observed changes. We suggest that the processes we analyse on a national scale could be taking place in Europe on a continental scale, and will most likely occur in the future in other regions of the world, with currently growing economies.
... pre-industrial era). This limitation is a common issue in studies of long-term biodiversity change (but see ref. 53 ) that can have a detrimental effect in restoration ecology 54,55 . The lack of baseline data could be overcome by the integration of ecological and paleobiological approaches (e.g. ...
Local biodiversity trends over time are likely to be decoupled from global trends, as local processes may compensate or counteract global change. We analyze 161 long-term biological time series (15–91 years) collected across Europe, using a comprehensive dataset comprising ~6,200 marine, freshwater and terrestrial taxa. We test whether (i) local long-term biodiversity trends are consistent among biogeoregions, realms and taxonomic groups, and (ii) changes in biodiversity correlate with regional climate and local conditions. Our results reveal that local trends of abundance, richness and diversity differ among biogeoregions, realms and taxonomic groups, demonstrating that biodiversity changes at local scale are often complex and cannot be easily generalized. However, we find increases in richness and abundance with increasing temperature and naturalness as well as a clear spatial pattern in changes in community composition (i.e. temporal taxonomic turnover) in most biogeoregions of Northern and Eastern Europe. The global biodiversity decline might conceal complex local and group-specific trends. Here the authors report a quantitative synthesis of longterm biodiversity trends across Europe, showing how, despite overall increase in biodiversity metric and stability in abundance, trends differ between regions, ecosystem types, and taxa.
... Invasion science has to acknowledge that even if there is excellent evidence of the native range for a given species, the idea of that location being the one in which the species should remain appears counter-intuitive and, in certain cases, very likely counterproductive. For example, rapid climate change and land-use change conflict with a static view of species' distributions (Webber & Scott 2012;Pecl et al. 2017;Hill & Hadly 2018;Silliman et al. 2018). As climate change and other stressors accumulate, species need to adapt, move on, or face extinction. ...
... killer whales and pinnipeds in the Shetland Islands; Deecke et al. 2011). These unexpected (and sometimes surprising) ecological interactions that emerge from conservation gains can have large impacts on the dynamics of ecosystem restoration (Doak et al. 2008, Silliman et al. 2018, Moxley et al. 2019. ...
White sharks Carcharodon carcharias and gray seals Halichoerus grypus are re-establishing their ecological roles within the Northwestern Atlantic Ocean, presenting an opportunity to understand gray seal movement and at-sea behavior under predation risk. As with other shark-seal hotspots, movements to and from terrestrial haul outs can be risky for gray seals, thereby eliciting antipredator strategies. We investigated the movement and coastal behavior of gray seals on Cape Cod (USA) in relation to seasonal and diel changes in white shark activity. Analyzing 412 trips to sea by 8 seals and more than 25000 acoustic detections from 23 individual white sharks, we observed seasonally homogeneous movements in seal behavior during months with greater shark presence. During riskier months, seal behavior manifested in near-exclusive nocturnal foraging, reduced offshore ranging, and limited at-sea activity. On these nocturnal trips to sea, seals returning to haul outs tended to avoid daybreak and traversed during diel minima in shark activity. However, seals tended to depart haul outs at dusk when shark presence was maximal. As conservation efforts succeed in rebuilding depleted populations of coastal predators, studying re-emerging predator-prey interactions can enhance our understanding about the drivers of movement and behavior.
... However, the generality of these chains of interactions, and how we might use them to benefit seagrass restoration, is not well-known. It is possible that predator introduction or recolonization might help stabilize or reverse seagrass decline in some places (Silliman et al., 2018). Predator addition is unlikely to be effective in areas where the cause of predator loss is unknown or seagrass has been completely lost, unless viable sources of propagules are nearby. ...
Seagrasses provide multiple ecosystem services including nursery habitat, improved water quality, coastal protection, and carbon sequestration. However, seagrasses are in crisis as global coverage is declining at an accelerating rate. With increased focus on ecological restoration as a conservation strategy, methods that enhance restoration success need to be explored. Decades of work in coastal plant ecosystems, including seagrasses, has shown that positive species relationships and feedbacks are critical for ecosystem stability, expansion, and recovery from disturbance. We reviewed the restoration literature on seagrasses and found few studies have tested for the beneficial effects of including positive species interactions in seagrass restoration designs. Here we review the full suite of positive species interactions that have been documented in seagrass ecosystems, where they occur, and how they might be integrated into seagrass restoration. The few studies in marine plant communities that have explicitly incorporated positive species interactions and feedbacks have found an increase in plant growth with little additional resource investment. As oceans continue to change and stressors become more prevalent, harnessing positive interactions between species through innovative approaches will likely become key to successful seagrass restoration.
... given its very intense biotic component. Finally, (i) the facts that the inferred mammoth steppe climatic niche is within the current climatic envelope of northern Siberia, Alaska and Yukon, and (ii) the state of the Arctic Holocene as a moist/ wet tundra-dominated interglacial [31] further agree with the hypothesis that the megafaunal extinctions of the LP/EH radically modified land cover and soil conditions in these regions, and that current terrestrial Arctic ecosystems might indeed be heavily affected by the 'ghosts of nature's past' [45]. ...
Natural climate solutions (NCS) in the Arctic hold the potential to be implemented at a scale able to substantially affect the global climate. The strong feedbacks between carbon-rich permafrost, climate and herbivory suggest an NCS consisting of reverting the current wet/moist moss and shrub-dominated tundra and the sparse forest–tundra ecotone to grassland through a guild of large herbivores. Grassland-dominated systems might delay permafrost thaw and reduce carbon emissions—especially in Yedoma regions, while increasing carbon capture through increased productivity and grass and forb deep root systems. Here we review the environmental context of megafaunal ecological engineering in the Arctic; explore the mechanisms through which it can help mitigate climate change; and estimate its potential—based on bison and horse, with the aim of evaluating the feasibility of generating an ecosystem shift that is economically viable in terms of carbon benefits and of sufficient scale to play a significant role in global climate change mitigation. Assuming a megafaunal-driven ecosystem shift we find support for a megafauna-based arctic NCS yielding substantial income in carbon markets. However, scaling up such projects to have a significant effect on the global climate is challenging given the large number of animals required over a short period of time. A first-cut business plan is presented based on practical information—costs and infrastructure—from Pleistocene Park (northeastern Yakutia, Russia). A 10 yr experimental phase incorporating three separate introductions of herds of approximately 1000 individuals each is costed at US$114 million, with potential returns of approximately 0.3–0.4% yr ⁻¹ towards the end of the period, and greater than 1% yr ⁻¹ after it. Institutional friction and the potential role of new technologies in the reintroductions are discussed.
This article is part of the theme issue ‘Climate change and ecosystems: threats, opportunities and solutions'.
... his plasticity is helping them to recover their population numbers and former geographical ranges (Jiménez et al. 2008, López-Martín andJiménez 2008). In fact, they are not only recovering their past ranges, but also colonizing and/or recolonizing new habitats (see Silliman et al. 2018 for a similar case with sea otters). One of the novel ecosystems (sensu Hobbs et al. 2009) that otters are increasingly using nowadays is reservoirs, used either for irrigation, water supply to cities or production of hydroelectric power. ...
The anthropic transformation of the landscape has brought the arrival of novel ecosystems. Since these ecosystems will likely become increasingly common in the future it is important to know if they can provide food for wildlife. Here we test whether European otters (Lutra lutra) can have high foraging success in human-made reservoirs. Rhythms of daily activity were studied in a small (365Ha) and shallow (6-15 m) reservoir in NW Spain in which otters show diurnal activity and can be observed directly when foraging. We studied time of permanence in the water and fish catch rate during the period in which water levels were kept artificially low (autumn-winter 2015, 2016 and 2017). Results indicate that otters had at least two peaks of diurnal activity (from 10:00 to11:00 am far from sunrise and from 6:00 to 7:00 pm immediately before sunset). Otters spent an average of 74 min (54 – 94, 95% CI) in the water foraging daily, and had a minimum fish catch rate of ca. 600 g/h of small fish. According to a pre-existing theoretical model, otters eating at that rate can satisfy their daily energy requirements with just 1.5 hours of daily foraging activity, what roughly coincides with the upper confidence limit of the parameter estimate. When considering as well the capture of large fish otters obtained ca. 850 g of fish per day in only 1.2 h in the water. Otters in the reservoir satisfy their daily requirements in autumn-winter with the same time investment than Shetland Island otters foraging during the day on marine fish during the summer. This coincidence is most likely due to the fact that winter water temperature in our study site is similar to that in the Shetland Islands in summer.
... Invasion science has to acknowledge that even if there is excellent evidence of the native range for a given species, the idea of that location being the one in which the species should remain appears counter-intuitive and, in certain cases, very likely counterproductive. For example, rapid climate change and land-use change conflict with a static view of species' distributions (Webber & Scott 2012;Pecl et al. 2017;Hill & Hadly 2018;Silliman et al. 2018). As climate change and other stressors accumulate, species need to adapt, move on, or face extinction. ...
A species is not native outside its native range, but native range is not precisely defined. The invasion literature contains wide discussion of the core concepts such as naturalization, invasiveness, and ecological impact, but the concept of native range has received so little attention that a formal definition does not exist. I considered, among other impediments to a formal definition of native range, the sometimes arbitrariness of the spatial and temporal limits assigned to native range. Broad questions that remain include whether invasion theory can be used to define the native range for species without non-native ranges.
© 2019 Society for Conservation Biology.
... Rising novelty challenges ecological management (Bonebrake et al. 2017), partly because ecosystems with high novelty can exhibit unexpected behavior due to new species interactions (Blois et al. 2013, Silliman et al. 2018, placing ecosystem services at risk. The predictive ability of ecological forecasting models is typically low when future conditions are outside of the range of observations used to test and calibrate such models (Veloz et al. 2012, Seidl et al. 2015, Keeley and Syphard 2016, Maguire et al. 2016, Uribe-Rivera et al. 2017. ...
Multiple global change drivers are increasing the present and future novelty of environments and ecological communities. However, most assessments of environmental novelty have focused only on future climate and were conducted at scales too broad to be useful for land management or conservation. Here, using historical county‐level datasets of agricultural land use, forest composition, and climate, we conduct a regional‐scale assessment of environmental novelty for Wisconsin landscapes from ca. 1890 to 2012. Agricultural land‐use data include six cropland types, livestock densities for four livestock species, and human populations. Forestry data comprise biomass‐weighted relative abundances for 15 tree genera. Climate data comprise seasonal means for temperature and precipitation. We found that forestry and land use are the strongest cause of environmental novelty (NoveltyForest=3.66, NoveltyAg.=2.83, NoveltyClimate=1.60, with Wisconsin's forests transformed by early 20th‐century logging and its legacies and multiple waves of agricultural innovation and obsolescence. Climate change is the smallest contributor to contemporary novelty, with precipitation signals stronger than temperature. Magnitudes and causes of environmental novelty are strongly spatially patterned, with novelty in southern Wisconsin roughly twice that in northern Wisconsin. Forestry is the most important cause of novelty in the north, land use and climate change are jointly important in the southwestern Wisconsin, and land use and forest composition are most important in central and eastern Wisconsin. Areas of high regional novelty tend also to be areas of high local change, but local change has not pushed all counties beyond regional baselines. Seven counties serve as the best historical analogues for over half of contemporary Wisconsin counties (40/72), and so can offer useful historical counterparts for contemporary systems and help managers coordinate to tackle similar environmental challenges. Multi‐dimensional environmental novelty analyses, like those presented here, can help identify the best historical analogues for contemporary ecosystems, places where new management rules and practices may be needed because novelty is already high, and the main causes of novelty. Separating regional novelty clearly from local change and measuring both across many dimensions and at multiple scales thus helps advance ecology and sustainability science alike. This article is protected by copyright. All rights reserved.
... Formerly persecuted wildlife, including large carnivores and large herbivores, are making a comeback on several continents (Enserink and Vogel, 2006;Fernández-Gil et al., 2010;Deinet et al., 2013;Fernández-Gil, 2014). Studying these species in recovery, major shifts in habitat selection and behaviour in European and North American wildlife have been identified (Martínez-Abraín, 2018;Silliman et al., 2018). Many large birds and mammal species, for instance, are now present in habitats that they used to occupy long ago or in new anthropic landscapes, thanks in large part to changed human attitudes towards wildlife. ...
... Formerly persecuted wildlife, including large carnivores and large herbivores, are making a comeback on several continents (Enserink and Vogel, 2006;Fernández-Gil et al., 2010;Deinet et al., 2013;Fernández- Gil, 2014). Studying these species in recovery, major shifts in habitat selection and behaviour in European and North American wildlife have been identified (Martínez-Abraín, 2018;Silliman et al., 2018). Many large birds and mammal species, for instance, are now present in habitats that they used to occupy long ago or in new anthropic landscapes, thanks in large part to changed human attitudes towards wildlife. ...
Forest insect pests are becoming increasingly common in Europe. A recent paper published in this journal dealt with a particular case of pest spreading in Portuguese coniferous forests.
The authors discussed the effect that mass trapping and clear‐cut belts had on slowing down the invasion and suggested that likely causes of pest spreading are stress due to global warming and the introduction of exotic species. Inspired by that paper, we defend here the point that forest communities are not only regulated by bottom‐up mechanisms, such as water stress, but also by top‐down mechanisms, such as predation.
We provide information from European metadata showing that forest biomass grew by 38% (1991–2015) whereas forest insectivorous passerine trends were stable (1980–2016).
Synthesis and applications . We suggest that rebounding European forests are too young to support large communities of insectivorous birds and that an effective way to solve pest problems could be to promote the use of nest boxes for them (and for other insect predators), as it was done in the past in large reforestations implemented in Spain. Additionally, the presence of large mammalian herbivores is needed to reduce the density of trees in forests. Priority should be given to this ecological management in comparison with massive trapping and clear‐cut belt construction or at least it should be used together with those engineering practices.
... Across terrestrial and marine ecosystems, ranges of large-bodied and highly migratory top predators often encompass vast geographic areas spanning multiple habitat types (Ripple et al. 2014, Silliman et al. 2018. Because top consumers face a disproportionately high risk of extinction compared to many lower trophic levels (Estes et al. 2011), understanding which habitats these top consumers rely on is critical for facilitating conservation and ultimately recovery. ...
... Beyond well-warranted celebrations, these successful conservation efforts often yield unintended consequences, both ecological and societal . For example, in many cases, recovery leads to increases in human-wildlife conflict, claims of overabundance, and public calls for changes to existing conservation policies (Roman et al. 2015, Silliman et al. 2018. ...
Recent species recoveries following historical depletion have been widely celebrated as conservation success stories. However, the recovery of highly interactive species, particularly predators, generates new management challenges that arise from their potential for wide‐ranging effects on local ecosystems and their poorly understood ecology. In marine systems, many pinniped species share parallel histories of depletion, recovery, and human conflict. Recovering from post‐exploitation populations of small size, these pinnipeds have returned to their present abundance from a largely absent, or severely reduced, recent role in many coastal ecosystems. To address the challenges arising today from real or perceived overabundance of protected pinniped species, we evaluate the prehistorical, historical, and contemporary abundances of six pinniped species that breed in the contiguous United States. This review highlights gaps in current knowledge that limit the implementation of ecologically grounded approaches to adaptive management of protected species in a time of shifting, or lifting, baselines. To address these gaps will require a diverse cadre of natural and social scientists as well as stakeholders to tackle the questions of how we define recovery at a species or ecosystem level, and when we have reached this point, how we move forward in a way that does not repeat a history of depletion, conservation, and recovery. Doing so will require an understanding of what role highly interactive species play in their ecosystems and how this role shifts with changes in ecological context, as well as the sociological and economic impacts of species restoration to humans. This knowledge is integral to the ongoing transition from a focus on preventing species extinction to new, and often unanticipated, challenges arising from the functional implications of species recovery.
... Looking ahead, "rope-less" fishing gear (6) and real-time data sharing (7) offer hope for resuming recovery. Reduced productivity and increased mortality may necessitate recalibrating recovery timelines (8) compared to original projections (9). ...
Ocean recoveries are moving targets
As the human population has grown, our demands on the ocean have increased rapidly. These demands have similarly increased the pressure we place on these systems, and we now cause considerable damage globally. If we want to maintain healthy ocean ecosystems into the future, we must learn to use ocean resources in a sustainable way and facilitate recovery in regions that have declined. Determining how to make these goals a reality, however, is no small challenge. Ingeman et al. review the challenge presented by attempting both to recover and to use ecosystems simultaneously and discuss several approaches for facilitating this essential dual goal.
Science , this issue p. eaav1004
... These challenges are not unique to the land. The same type of conflicts exist in the ocean, but this has yet to be elevated as a global issue despite its potential for rapid increase in various marine systems and across several species (Fig. 1) [2][3][4]. ...
Human-wildlife conflict has been receiving increased scientific and management attention, predominantly in terrestrial systems, as a side effect of successful predator conservation and recovery. These same conflicts exist in the ocean; however, they are mostly regarded in a region- or taxa-specific context despite evidence that human-wildlife conflict is prevalent across the global oceans and likely to increase as a result of successful conservation measures. Can the lessons learned from conflicts on land promote more sustainable success in the sea? Or, do ocean human-wildlife conflicts create unique challenges that require new solutions? This paper synthesizes evidence from human-wildlife conflicts in the ocean and provides initial suggestions for progressing with effective management in the ocean. Humans have extensive experience managing conflict with terrestrial predators and several of the strategies are transferable to marine predators, but several important differences between systems necessitate a marine-specific focus and evaluation of existing mitigation strategies. Further, in managing marine wildlife conflict, it is crucial to recognize that perceived conflicts can be just as important as actual conflict and that, in many cases, human-human conflict is at the root of human-wildlife conflict. As efforts to recover important predator populations continue, humans are faced with the exciting opportunity and a new necessity to constructively manage these recoveries to continue to meet goals for marine conservation while simultaneously promoting human safety and industry in the seas.
... This concept has been applied to the extant Earth-bioshell in the form of a guessed/informed estimation of "climate velocities" (Trisos et al., 2018), the so-called suspected speed and directions that suffering existing species need to migrate geographically in order to track barely perceptible changes in climate (Reddin et al., 2018); (III) plentiful but slowly poisonous grazed plants, coupled with dinosaurian insensitivity and forgetfulness, caused mass-starvation amongst the lumbering vegetation-gobbling critters (Frederick and Gallup, 2017). [Trisos and his colleagues failed to adequately factor in past and present-day human conservationist's efforts that have fostered a noticeable return of large mobile predators because of their increasing populations, stimulated by human protection, to the predator's formerly abandoned support ecosystems (Silliman et al., 2018).] You, the reader, name, or from within your own mind, conjure any additional dinosaur extinction hypothesis and it has already likely to have been researched by some investigator with fantastically fervid intensity! ...
Coastal habitat loss has led to declines in many higher trophic level predators. These declines can be mitigated through habitat restoration, which putatively enhances predator populations and trophic dynamics by creating foraging opportunities in reestablished habitat, but this lacks empirical support. Here, we assess the prediction restored coastal habitat supports sportfish feeding relationships similar to natural habitat, at restored oyster reefs ( Crassostrea virginica ) and living shoreline habitats in Florida, U.S.A. Stable isotopes and gut contents were analyzed from young sportfish (i.e. predatory fish targeted by anglers) collected at control and restored sites for up to 3 years. The influence of habitat features, predator size, and prey availability on carbon and nitrogen isotope values were examined using a model species (mangrove/gray snapper [ Lutjanus griseus ]). In summary, sportfish species had distinct isotopic values, consuming similar prey but in different proportions between habitats. Prey abundance and richness, and reef height were influential predictors of L. griseus stable isotope values, with restored reefs contributing to their diet more than controls according to Bayesian mixing models. The trophic niche area of L. griseus and their predominant prey achieved trophic equivalence between restored and natural oyster reefs within 1 year following restoration. Stabilized living shorelines attained trophic equivalency to natural shorelines, but may take longer to accrue prey for some species. These findings generate fundamental ecological knowledge and actionable science, including targets, timelines, and indicator species, that natural resource managers and restoration practitioners can use to assess trophic structure and success of coastal habitat restoration.
Since 1970, there has been an overall decline in wildlife populations in the order of 52%. Freshwater species populations have declined by 76%; species populations in Central and South America have declined by 83%; and in the Indo-Pacific by 67%. These are often not complete extinctions, but large declines in the numbers of animals in each species, as well as habitat loss. This presents us with a tremendous opportunity, before it is too late to rescue many species. This book documents the present state of wildlife on a global scale, using a taxonomic approach, and serving as a one stop place for people involved in conservation to be able to find out what is in decline, and the success stories that have occurred to bring back species from the brink of extinction - primarily due to conservation management techniques - as models for what we might achieve in the future.
The current warming of the Mediterranean Sea has been forecast to lead to the shrinkage of seagrass meadows. We agree that rising sea temperatures most likely will have immediate negative effects on them because present-day asexually reproducing clones of Posidonia oceanica were likely selected as a form of resistance under suboptimal conditions during the colder temperatures of the last glaciation. However, since the evolution of P. oceanica has happened under tropical/subtropical conditions for tens of millions of years, some kind of evolutionary resilience to high temperatures is to be expected. We suggest that the ability of P. oceanica plants to reproduce sexually when water temperature is >27°C might lead in the future to the selection of warm-loving plants (as warm-sensitive clones decline), with an associated increase in genetic variability in the species gene pool. Predictions focused exclusively on the future decline of cold-selected (warm-sensitive) clones may result in short-sighted forecasts because the deep history of the taxon is overlooked. We suggest that an evolutionary-based approach should be more often considered when analysing the present declines of animal and plant species. We provide some additional examples of cases in which this could be done.
Behavioral adaptations for maintaining breathing holes in sea ice and lairs in the overlying snow cover allow ringed seals to occupy sea ice environments from which other marine mammals are excluded for much of the year. The broad distribution of ringed seals in the ice-covered seas of the northern hemisphere created a niche for an apex predator, and polar bears have evolved as specialists preying on ringed seals. The earliest occupation of the Arctic by people, likewise, depended heavily on the year-round availability of ringed seals. Reliance on breathing holes limits ringed seal movements for as much as 9 months of the year, with implications for foraging and reproductive behaviors as well as for predator avoidance. Ringed seals forage throughout the year with the greatest intake during a brief foraging period between the breakup and subsequent formation of sea ice. Predator avoidance appears to explain the allocation of time better than optimal foraging, at least during ice-bound periods. The under-ice behavior of breeding adults is more consistent with mate or resource guarding than with territoriality as a mating strategy. Feeding through lactation requires a trade-off between time spent foraging and attendance of pups vulnerable to predation. Ringed seals are becoming more vulnerable to predators in the water and on the ice as refuge on ice and under snow diminishes in a warming Arctic.Keywords
Pusa hispida
Sea iceSnow coverSite fidelityMate guardingNavigationForagingPredator avoidanceTrade-offs
Consumers can structure plant communities and may function as keystone species or ecosystem engineers. In salt marshes, the prevailing paradigm has shifted in recent decades from nearly complete focus on bottom‐up processes to inclusion of top‐down effects. Although the number of studies investigating top‐down control continues to climb, few experiments span multiple years, so temporal variability in or long‐term impacts of consumers have not been well characterized. In addition, while top‐down control has been found to be common in Western and Eastern Atlantic and Western Pacific salt marshes, our study is one of the first to experimentally consider top‐down control of salt marsh plants in the Eastern Pacific. We conducted a five‐year field experiment along eroding creekbank edges of a California salt marsh in which we manipulated densities of the shore crab, Pachygrapsus crassipes, and tracked marsh responses over time. Our results demonstrate that, through both consumption and engineering activities, this superabundant crab is regulating marsh vegetation and soil structure. Experimentally reducing crab abundance enhanced vegetation biomass and sediment bulk density. Moreover, root biomass and bulk density—factors known to increase marsh resilience to erosion and sea‐level rise—decreased linearly with increasing burrow density. Our long‐term study uniquely revealed that burrows can persist for years after crab abundances are reduced and that plant responses from grazer exclusions gradually strengthen over time, likely due to the relatively slow growth of woody perennial foundational plants. Since shore crabs are abundant throughout the marsh in most major estuaries within the range of the species (from Baja California, Mexico to Oregon, USA), we hypothesize that this species is exerting significant, yet underappreciated top‐down control and modifying the sediment properties of many West Coast salt marshes.
Global environmental changes have accelerated at an unprecedented rate in recent decades due to human activities. As a consequence, the incidence of novel abiotic conditions and biotic communities, which have been continuously emerging in the Earth system, has rapidly risen. Despite growing attention to the incidence and challenges posed by novelty in terrestrial ecosystems, novelty has not yet been quantified in marine ecosystems. Here, we measured for the rate of novelty (RoN) in abiotic conditions and community structure for three trophic levels, i.e., phytoplankton, zooplankton, and fish, in a large marine system ‐ the Baltic Sea. We measured RoN as the degree of dissimilarity relative to a specific spatial and temporal baseline, and contrasted this with the rate of change as a measure of within‐basin change over time. We found that over the past 35 years abiotic and biotic RoN showed complex dynamics varying in time and space, depending on the baseline conditions. RoN in abiotic conditions was smaller in the open Central Baltic Sea than in the Kattegat and the more enclosed Gulf of Bothnia, Gulf of Riga, and Gulf of Finland in the north. We found a similar spatial pattern for biotic assemblages, which resulted from changes in composition and stock size. We identified sea‐surface temperature and salinity as key drivers of RoN in biotic communities. Hence, future environmental changes that are expected to affect the biogeochemistry of the Baltic Sea, may favor the rise of biotic novelty. Our results highlighted the need for a deeper understanding of novelty development in marine ecosystems, including interactions between species and trophic levels, ecosystem functioning under novel abiotic conditions, and considering novelty in future management interventions.
The presence of well-documented sites in the Americas predating and south of the opening of an ice-free corridor in the North American ice sheets lends credence to a Pacific coastal migration theory (CMT) explaining the route for the initial peopling of the Americas. This theory has been informally discussed for more than 50 years, but until recently, has been largely ignored and never properly defined as a result. We provide a formal definition of the CMT which, briefly stated, is that Upper Paleolithic populations
moved from Asia to coastal regions along the northwestern Pacific Rim between ~45-30 ka. By ~30 ka these coastal populations developed a mixed maritime, nearshore, and terrestrial adaptation involving the use of boats, shell fishhooks for deep-water fishing, and a stemmed point and macroblade core technology. About 25-24 ka a subset of these coastal populations became isolated somewhere in the vicinity of the Japan/Paleo-Hokkaido, Sahkalin, Kuril (PSHK) region, developing genetically into the ancient Native American (ANA) populations that eventually settled the Americas. Between ~22-16 ka these ANA people began migrating by foot and boat along the southern Beringian coast and down the Alaskan and Canadian coastline into the Americas south of the continental ice sheets before eventually expanding inland. We develop a series of testable hypotheses through which the CMT can be examined.
Large predators play important ecological roles, yet many are disproportionately imperiled. In marine systems, artificial reefs are often deployed to restore degraded reefs or supplement existing reefs, but it remains unknown whether these interventions benefit large predators. Comparative field surveys of thirty artificial and natural reefs across ~200 km of the North Carolina, USA coast revealed large reef-associated predators were more dense on artificial than natural reefs. This pattern was associated with higher densities of transient predators (e.g. jacks, mackerel, barracuda, sharks) on artificial reefs, but not of resident predators (e.g., grouper, snapper). Further analyses revealed that this pattern of higher transient predator densities on artificial reefs related to reef morphology, as artificial reefs composed of ships hosted higher transient predator densities than concrete reefs. The strength of the positive association between artificial reefs and transient predators increased with a fundamental habitat trait-vertical extent. Taller artificial reefs had higher densities of transient predators, even when accounting for habitat area. A global literature review of high trophic level fishes on artificial and natural habitats suggests that the overall pattern of more predators on artificial habitats is generalizable. Together, these findings provide evidence that artificial habitats, especially those like sunken ships that provide high vertical structure, may support large predators.
Restoration ecologists have long-called for more holistic approaches to ecosystem restoration and tools for monitoring restoration success. There has been an increased number of restoration projects assessing ecosystem-scale processes, such as nutrient cycling and productivity. However, an examination of trophic interactions (e.g., trophic position, linkages, and diversity) as a tool for assessing restoration success is limited and can provide a more complete depiction of restoration success when coupled with traditional community metrics. Here, the impact of habitat restoration on trophic recovery was assessed through a targeted literature review, analyzing how trophic structure responds to habitat restoration over time, compared to control sites, and viewed across ecosystems. Overall, trophic structure recovers following restoration but may require several years. Comparing systems, restoration of trophic structure in terrestrial environments has received less attention (19%) as compared to freshwater (31%) and coastal (50%) systems. Community metrics and stable isotopes were the most common methods for assessing trophic interactions and will likely continue to be valuable tools when assessing how restoration impacts ecosystems. In terms of best practices to achieve and quantify trophic restoration success, future studies should increase frequency and duration of pre- and post-restoration monitoring, establish consistency in selecting control sites, and incorporate habitat structural elements compatible with restoration to attract higher trophic level species. The inclusion of trophic interactions in restoration projects generates a more comprehensive understanding of trophic structure and ecosystem function and offers insights to develop more effective management strategies for achieving long-term restoration success.
Large‐bodied predators are well represented among the world's threatened and endangered species. A significant body of literature shows that in terrestrial and marine ecosystems large predators can play important roles in ecosystem structure and functioning. By contrast, the ecological roles and importance of large predators within freshwater ecosystems are poorly understood, constraining the design and implementation of optimal conservation strategies for freshwater ecosystems. Conservationists and environmentalists frequently promulgate ecological roles that crocodylians are assumed to fulfil, but often with limited evidence supporting those claims.
Here, we review the available information on the ecological importance of crocodylians, a widely distributed group of predominantly freshwater‐dwelling, large‐bodied predators. We synthesise information regarding the role of crocodylians under five criteria within the context of modern ecological concepts: as indicators of ecological health, as ecosystem engineers, apex predators, keystone species, and as contributors to nutrient and energy translocation across ecosystems. Some crocodylians play a role as indicators of ecosystem health, but this is largely untested across the order Crocodylia. By contrast, the role of crocodylian activities in ecosystem engineering is largely anecdotal, and information supporting their assumed role as apex predators is currently limited to only a few species. Whether crocodylians contribute significantly to nutrient and energy translocation through cross‐ecosystem movements is unknown.
We conclude that most claims regarding the importance of crocodylians as apex predators, keystone species, ecosystem engineers, and as contributors to nutrient and energy translocation across ecosystems are mostly unsubstantiated speculation, drawn from anecdotal observations made during research carried out primarily for other purposes. There is a paucity of biological research targeted directly at: understanding population dynamics; trophic interactions within their ecological communities; and quantifying the short‐ and long‐term ecological impacts of crocodylian population declines, extirpations, and recoveries. Conservation practices ideally need evidence‐based planning, decision making and justification. Addressing the knowledge gaps identified here will be important for achieving effective conservation of crocodylians.
Cross-ecosystem movements of mobile consumers are a primary mechanism by which energy and nutrients are exchanged between disparate ecosystems. While factors influencing variation in bottom–up subsidies between ecosystems have been well studied, much less is known regarding how biotic and abiotic factors influence the dynamics of mobile consumer-driven connectivity. In a literature survey, we found only 14% of studies examined factors contributing to variation in cross-ecosystem marine foraging by freshwater-adapted consumers. Here, we examine the relationships between abiotic factors and cross-ecosystem movements of a highly mobile freshwater-adapted top predator, Alligator mississippiensis (American alligator). As alligators lack physiological adaptations to survive in marine environments, we predict this linkage would be affected by factors that modify the ability to cope with high salinities. Our results reveal that multiple abiotic factors (e.g., relative humidity, temperature, total precipitation) are key explanatory variables of the duration of cross-ecosystem foraging trips by alligators, and that the absence of salt glands does not preclude them from performing long forays into marine environments. More broadly, our results expand our understanding of mobile consumer-driven ecosystem connectivity at the land–sea interface by demonstrating connectivity is highest when physical stressors are relaxed, and access to and availability of resources are maximized.
Consequences of shifting species distributions
Climate change is causing geographical redistribution of plant and animal species globally. These distributional shifts are leading to new ecosystems and ecological communities, changes that will affect human society. Pecl et al. review these current and future impacts and assess their implications for sustainable development goals.
Science , this issue p. eaai9214
Rapid and ongoing change creates novelty in ecosystems everywhere, both when comparing contemporary systems to their historical baselines, and predicted future systems to the present. However, the level of novelty varies greatly among places. Here we propose a formal and quantifiable definition of abiotic and biotic novelty in ecosystems, map abiotic novelty globally, and discuss the implications of novelty for the science of ecology and for biodiversity conservation. We define novelty as the degree of dissimilarity of a system, measured in one or more dimensions relative to a reference baseline, usually defined as either the present or a time window in the past. In this conceptualization, novelty varies in degree, it is multidimensional, can be measured, and requires a temporal and spatial reference. This definition moves beyond prior categorical definitions of novel ecosystems, and does not include human agency, self-perpetuation, or irreversibility as criteria. Our global assessment of novelty was based on abiotic factors (temperature, precipitation, and nitrogen deposition) plus human population, and shows that there are already large areas with high novelty today relative to the early 20th century, and that there will even be more such areas by 2050. Interestingly, the places that are most novel are often not the places where absolute changes are largest; highlighting that novelty is inherently different from change. For the ecological sciences, highly novel ecosystems present new opportunities to test ecological theories, but also challenge the predictive ability of ecological models and their validation. For biodiversity conservation, increasing novelty presents some opportunities, but largely challenges. Conservation action is necessary along the entire continuum of novelty, by redoubling efforts to protect areas where novelty is low, identifying conservation opportunities where novelty is high, developing flexible yet strong regulations and policies, and establishing long-term experiments to test management approaches. Meeting the challenge of novelty will require advances in the science of ecology, and new and creative conservation approaches.
Alligator mississippiensis generally occurred in very low densities, usually <0.2 ind/km. -P.J.Jarvis
The Gulf Coastal Plain of Texas was populated by hunter-gatherers from the Early Archaic (ca. 7000 B. P.) through to the Late Prehistoric period (ca. A. D. 700-1400). In order to characterize past dietary adaptations along the coast and further inland, stable isotopes of carbon and
nitrogen were analyzed in preserved bone from 198 individuals from mortuary sites. In addition, 140 samples of faunal bone were analyzed to elucidate the stable isotope ecology for each region. The results indicate long-term stability in dietary adaptations with regional variation among coastal,
riverine, and inland groups, including an early and, substantial, use of freshwater and marine resources. There is also evidence for constrained mobility and increasing use of plant resources within regions as populations increased in size and density.
Alligators and crocodiles differ in their physiological capacity to live in saline waters.
Crocodiles can tolerate high-salinity water, at least for limited timeframes, whereas alligators and
their close relatives cannot. Experiments have placed different crocodylians in various water
salinities to document physiological responses, but no study has estimated the extent to which natural
populations of crocodylids can live independent of fresh water. Here we estimated marine
food and perhaps seawater contributions to a population of American crocodile Crocodylus acutus
in southernmost Florida, USA. We evaluated the use of carbon, oxygen, and strontium isotopes as
tracers of marine versus terrestrial sources. We compared C. acutus isotopic values to those of
marine reptiles (marine iguanas and Pacific loggerhead turtles) and to American alligators, which
require fresh water. We found that freshwater reptiles can be discriminated from those that drink
seawater (or survive on metabolic and prey-included water in saline habitats) based on the magnitude
of population-level oxygen isotope variation in bioapatite, whereas mean carbon isotope
values discriminate between marine versus terrestrial food consumption. We used a 2 endmember
(seawater and fresh water) mixing model to calculate percentage of marine resources
used by C. acutus. Results indicate that adult C. acutus in southern Florida use marine food about
65% of the time and seawater or water gleaned from marine food about 80% of the time. This suggests
that behavioral osmoregulatory techniques (i.e. seeking fresh water specifically for drinking,
as suggested by other researchers) may not be necessary and that C. acutus is capable of being
largely ecologically independent of fresh water.
Area of home range (H) can be related empirically to body weight (W) by the formulation H = aW^k. The computed values of exponent k have generated controversy concerning potential differences between trophic groups and whether they differ from 0.75 (the value expected if area of home range is a function of basal metabolic rate). When large mammals are considered, the empirical relationship assumes the form H = .002W^1^.^0^2 for herbivores, H = .059W^.^9^2 for omnivores, and H = .11W^1^.^3^6 for carnivores. By treating the animal's energetic requirements and the productivity of its habitat explicitly, empirical values of k > 0.75 are shown to result from declining rates of production of utilizable energy per unit area of habitat with increasing body weight. While trophic status and weight modify the utilizable proportion of energy in the habitat, broad correlations also exist between size of home range and surrogate variables for productivity (precipitation and latitude). Differences in weight alone account for a large portion of the differences between male and female or subadult and adult home ranges. Behavioral phenomena need not be invoked. Differences between herbivores and carnivores are in the direction suggested for birds and mammals. Criticisms regarding inter-class and inter-tropic comparisons appear resolved.
Africa's large predator guild (lion, Panthera leo; leopard, Panthera pardus; spotted hyaena, Crocuta crocuta; cheetah, Acinonyx jubatus, and African wild dog, Lycaon pictus) occurs sympatrically with high dietary overlap. Temporal partitioning could facilitate coexistence, but there has been no study testing this or the factors that may Influence the evolution of predator activity patterns. The activity patterns of Africa's large predators were reviewed, using published sources, and the degree of activity overlap was assessed. Six hypotheses were made based on three hypotheses of factors driving the evolution of predator activity patterns: Increased foraging success, and scramble and Interference competition. All predators exhibited a degree of crepuscular behaviour, supporting hypotheses relating to increased hunting success. Nocturnal predators exhibit decreased activity at the darkest times of night due to visual limitations. There was no support for the hypothesis that predators would be active at the same time as their main prey species. Although all members of the guild suffer intraguild predation, only subordinate members exhibited scramble competition avoidance by minimizing activity at the same times as their intraguild predators. Subordinate predators (wild dogs and cheetahs), frequently reported as suffering from kleptoparasitism, minimize simultaneous activity with major kleptoparasites (lions and spotted hyaenas). These latter top predators have high dietary overlap; however, they do not avoid Interference competition by minimizing activity overlap. Thus, optimal activity patterns evolved to satisfy a diverse range of factors that differ amongst species. Competition avoidance is the primary cause of the temporal partitioning in activity between subordinate and top predators. Africa's carnivores have also evolved morphological adaptations to their activity patterns reflecting the length of time they have occurred in sympatry.
Until recently, large apex consumers were ubiquitous across the globe and had been for millions of years. The loss of these
animals may be humankind’s most pervasive influence on nature. Although such losses are widely viewed as an ethical and aesthetic
problem, recent research reveals extensive cascading effects of their disappearance in marine, terrestrial, and freshwater
ecosystems worldwide. This empirical work supports long-standing theory about the role of top-down forcing in ecosystems but
also highlights the unanticipated impacts of trophic cascades on processes as diverse as the dynamics of disease, wildfire,
carbon sequestration, invasive species, and biogeochemical cycles. These findings emphasize the urgent need for interdisciplinary
research to forecast the effects of trophic downgrading on process, function, and resilience in global ecosystems.
After nearly a century of recovery from overhunting, sea otter populations are in abrupt decline over large areas of western Alaska. Increased killer whale predation is the likely cause of these declines. Elevated sea urchin density and the consequent deforestation of kelp beds in the nearshore community demonstrate that the otter's keystone role has been reduced or eliminated. This chain of interactions was probably initiated by anthropogenic changes in the offshore oceanic ecosystem.
There is now ample evidence of the ecological impacts of recent climate change, from polar terrestrial to tropical marine environments. The responses of both flora and fauna span an array of ecosystems and organizational hierarchies, from the species to the community levels. Despite continued uncertainty as to community and ecosystem trajectories under global change, our review exposes a coherent pattern of ecological change across systems. Although we are only at an early stage in the projected trends of global warming, ecological responses to recent climate change are already clearly visible.
Detailed postmortem examination of southern sea otters (Enhydra lutris nereis) found along the California (USA) coast has provided an exceptional opportunity to understand factors influencing survival in this threatened marine mammal species. In order to evaluate recent trends in causes of mortality, the demographic and geographic distribution of causes of death in freshly deceased beachcast sea otters necropsied from 1998-2001 were evaluated. Protozoal encephalitis, acanthocephalan-related disease, shark attack, and cardiac disease were identified as common causes of death in sea otters examined. While infection with acanthocephalan parasites was more likely to cause death in juvenile otters, Toxoplasma gondii encephalitis, shark attack, and cardiac disease were more common in prime-aged adult otters. Cardiac disease is a newly recognized cause of mortality in sea otters and T. gondii encephalitis was significantly associated with this condition. Otters with fatal shark bites were over three times more likely to have pre-existing T. gondii encephalitis suggesting that shark attack, which is a long-recognized source of mortality in otters, may be coupled with a recently recognized disease in otters. Spatial clusters of cause-specific mortality were detected for T. gondii encephalitis (in Estero Bay), acanthocephalan peritonitis (in southern Monterey Bay), and shark attack (from Santa Cruz to Point Año Nuevo). Diseases caused by parasites, bacteria, or fungi and diseases without a specified etiology were the primary cause of death in 63.8% of otters examined. Parasitic disease alone caused death in 38.1% of otters examined. This pattern of mortality, observed predominantly in juvenile and prime-aged adult southern sea otters, has negative implications for the overall health and recovery of this population.
Saiga antelope (Saiga tatarica) is one of the typical late Pleistocene species of the cold and arid mammoth steppe that covered a large area of northern hemisphere. The species is currently endangered and persists only in small areas of Central Asian steppe and desert ecosystems. The investigation of the ecology of the Pleistocene saiga using stable isotope ratios (13C, 15N) aimed to decipher how different their diet and habitat were from those observed nowadays in relict populations. Up to 76 samples of bone collagen of ancient saigafrom Western Europe, Siberia and Eastern Beringia were analysed and compared with samples of hair and bone collagen of modern specimens from Kazahkstan, Russia and Mongolia. The 13C values of the ancient saiga do not exhibit a clear trend over time. They cover the same range of values as the modern ones, from a C3-dominated to a C3-C4-dominated mixed diet (including probably Chenopodiaceae). In contrast, the 15N values of fossil saigas are more variable and lower on average than the extant ones. The lowest 15N values of ancient saiga are found around the Last Glacial Maximum, reflecting the influence of the cold conditions at that time. On the other hand, fossil saiga occupying the same regions as the historical and modern populations exhibit high 15N values similar to the modern ones, confirming ecological continuity over time. Modern saiga is thus occupying just one of its potential diverse habitats they used in the past. Therefore, the extant saiga is not a refugee species confined to a suboptimal habitat. During the late Pleistocene, the saiga occupied a separate niche compared with the other ungulates of the mammoth steppe. However, this species could also adapt to a lichen-dominated diet normally seen in reindeer, leading to an isotopic overlap between the two species in south-western France and Alaska around the Last Glacial Maximum. This adaptation allowed a geographical expansion that does not correspond to a habitat-tracking episode. Hence, the realized niche currently observed for the saiga is reduced compared with their potential capacity for adaptation, a crucially important factor for the conservation of this endangered species.
Although southern sea otters (Enhydra lutris nereis) are not considered prey for white sharks (Carcharodon carcharias), sharks do nonetheless bite sea otters. We analyzed spatial and temporal trends in shark bites on sea otters in California, assessing the frequency of shark bite wounds in 1,870 carcasses collected since 1985. The proportion of stranded sea otters having shark bites has increased sharply since 2003, and white shark bites now account for >50% of recovered carcasses. The trend was most pronounced in the southern part of the range, from Estero Bay to Point Conception, where shark bite frequency has increased eightfold. Seasonal trends were also evident: most shark-bitten carcasses are recovered in late summer and fall; however, the period of elevated shark bite frequency has lengthened. The causes of these trends are unclear, but possible contributing factors include increased white shark abundance and/or changes in white shark behavior and distribution. In particular, the spatiotemporal patterns of shark-bitten sea otters match increases in pinniped populations, and the increased availability of marine mammal prey for white sharks may have led to more sharks spending more time in nearshore waters utilized by both sea otters and pinnipeds.
Isotopic tracking of carnivore palaeoecology is a relatively new approach that yielded important results for the study of the non-analogue mammoth steppe biome. After describing the prerequisite to apply this approach and the possible complications, the main achievements will be described for extinct carnivore species such as scimitar-tooth cat Homotherium serum, cave lion Panthera spelaea, giant short-faced bear Arctodus simus, cave bear Ursus spelaeus s.l., as well as for ancient representatives of extant species such as brown bear Ursus arctos and wolf Canis lupus. Isotopic tracking showed that scimitar-tooth cats in Alaska were not specialist proboscidean predators but rather generalist consumers of other large herbivores. The majority of cave lions analysed so far were focused on reindeer, some individuals were specialized on cave bears, especially in contexts of competition with cave hyenas. Giant short-faced bears in Alaska were not pure herbivores and consumed meat from reindeer, muskoxen and possibly other predators, but may have still incorporated plant resources in their menu. In contrast, all cave bear populations studied so far for which a clear dietary reconstruction could be done were virtually pure herbivores, only a few cases are still unclear. Interestingly, brown bears used the opposite extreme of the dietary spectrum when competing with other large bears such as cave bears and giant short-faced bears, i.e. were more carnivorous in Europe and more herbivorous in Alaska. Finally wolves seem to have been outcompeted by hyenas but became dominant predators during the Lateglacial in Europe to the expense of the last cave lions. The results obtained through this approach are also relevant for improving conservation strategies of endangered extant large carnivores.
Cambridge Core - Ecology and Conservation - People and Wildlife, Conflict or Co-existence? - edited by Rosie Woodroffe
Large‐bodied, top‐predators are often highly mobile, with the potential to provide important linkages between spatially distinct food webs. What biological factors contribute to variation in cross‐ecosystem movements, however, have rarely been examined.
Here, we investigated how ontogeny (body size), sex and individual‐level behaviour impacts intrapopulation variation in cross‐ecosystem foraging (i.e. between freshwater and marine systems), by the top‐predator Alligator mississippiensis .
Field surveys revealed A. mississippiensis uses marine ecosystems regularly and are abundant in estuarine tidal creeks (from 0·3 to 6·3 individuals per km of creek, n = 45 surveys). Alligator mississippiensis captured in marine/estuarine habitats were significantly larger than individuals captured in freshwater and intermediate habitats.
Stomach content analysis (SCA) showed that small juveniles consumed marine/estuarine prey less frequently (6·7% of individuals) than did large juveniles (57·8%), subadult (73%), and adult (78%) size classes. Isotopic mixing model analysis ( SIAR ) also suggests substantial variation in use of marine/estuarine prey resources with differences among and within size classes between sexes and individuals (range of median estimates for marine/estuarine diet contribution = 0·05–0·76).
These results demonstrate the importance of intrapopulation characteristics (body size, sex and individual specialization) as key determinants of the strength of predator‐driven ecosystem connectivity resulting from cross‐ecosystem foraging behaviours. Understanding the factors, which contribute to variation in cross‐ecosystem foraging behaviours, will improve our predictive understanding of the effects of top‐predators on community structure and ecosystem function.
The 1995/1996 reintroduction of gray wolves (Canis lupus) into Yellowstone National Park after a 70 year absence has allowed for studies of tri-trophic cascades involving wolves, elk (Cervus elaphus), and plant species such as aspen (Populus tremuloides), cottonwoods (Populus spp.), and willows (Salix spp.). To investigate the status of this cascade, in September of 2010 we repeated an earlier survey of aspen and measured browsing and heights of young aspen in 97 stands along four streams in the Lamar River catchment of the park’s northern winter range. We found that browsing on the five tallest young aspen in each stand decreased from 100% of all measured leaders in 1998 to means of <25% in the uplands and <20% in riparian areas by 2010. Correspondingly, aspen recruitment (i.e., growth of seedlings/sprouts above the browse level of ungulates) increased as browsing decreased over time in these same stands. We repeated earlier inventories of cottonwoods and found that recruitment had also increased in recent years. We also synthesized studies on trophic cascades published during the first 15 years after wolf reintroduction. Synthesis results generally indicate that the reintroduction of wolves restored a trophic cascade with woody browse species growing taller and canopy cover increasing in some, but not all places. After wolf reintroduction, elk populations decreased, but both beaver (Caster canadensis) and bison (Bison bison) numbers increased, possibly due to the increase in available woody plants and herbaceous forage resulting from less competition with elk. Trophic cascades research during the first 15 years after wolf reintroduction indicated substantial initial effects on both plants and animals, but northern Yellowstone still appears to be in the early stages of ecosystem recovery. In ecosystems where wolves have been displaced or locally extirpated, their reintroduction may represent a particularly effective approach for passive restoration.
This study explored how baboons, Papio cynocephalus ursinus , in a desert population trade off foraging and predation risk in patterns of habitat use. Four hypotheses were proposed and tested; that habitats are used on the basis of (1) availability, (2) foraging rewards (following the ideal free distribution), (3) foraging rewards modified by the constraints of nocturnal predation risk (partial trade-off) or (4) foraging rewards modified by the constraints of continuous predation risk (full trade-off). Food availability in each habitat was quantified through quadrat surveys describing stem density, plant part availability and nutrient availability (protein and energy) of key plant foods per unit area. Predation risk in each habitat was evaluated using measures describing the relative threat of attack and capture by both leopards, Panthera pardus , and lions, Panthera leo ; attack risk was determined on the basis of habitat visibility and predator ambush distances, while capture risk was calculated using a simple model incorporating predator and prey velocities, habitat visibility and nearest refuge distance. Patterns of baboon behaviour were assessed for adult males and females in four groups through day-follows and instantaneous sampling. The baboons did not use habitats directly in proportion to their availability in the group's ranging area (in contrast to hypothesis 1). Nor did patterns of habitat use match those expected on the basis of the ideal free distribution, either during all activities (hypothesis 2) or during feeding (hypothesis 3). Instead, the baboons spent less time feeding in the high-risk food-rich habitat but more time feeding in the low-risk relatively food-poor habitat. Baboons also preferred low-risk habitats in other activities, where during resting and grooming all habitats were avoided except the safest (where key food species were absent). These results support hypothesis 4. Deviations from these patterns by a unimale group indicate that male reproductive strategies may also play a role in habitat selection.
A comparison of western Aleutian Islands with and without sea otter populations shows that this species is important in determining littoral and sublittoral community structure. Sea otters control herbivorous invertebrate populations. Removal of sea otters causes increased herbivory and ultimately results in the destruction of macrophyte associations. The observations suggest that sea otter reestablishment indirectly affects island fauna associated with macrophyte primary productivity.
Enhydra lutris. The IUCN Red List of Threatened Species
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