Large-bodied Species Research Articles

Temporal variations in the pelagic fish community of Lake Winnipeg from 2002 to 2019

Lake Winnipeg has undergone extensive changes in environmental conditions and fish community structure during recent decades. The presence of cyanobacteria and invasive species as well as eutrophication, flow regulation, fishing pressure, and climate change all have potential impacts on the native fish community. Since 2002, pelagic forage fish species and early life stages of large-bodied fish species in the pelagic zone in Lake Winnipeg (Manitoba, Canada) have been monitored. Catch data were used to study the temporal variation in species-specific occurrence and catch-per-unit-effort (CPUE) and to analyse the effects of lake condition on species occurrence and CPUE estimates. To account for the temporal variation observed for commonly caught prey species in Lake Winnipeg, we used a Bayesian approach, Integrated Nested Laplace Approximation (INLA), to compare the effects of environmental variables on occurrence and CPUE. The pelagic fish community composition varied among years, and CPUE declined by 2.2-fold between 2005–2008 and 2015–2018. Emerald shiner was the most dominate prey fish species but decreased in the catches since the early 2000’s, while rainbow smelt have almost entirely disappeared from the catches in recent years. Overall, we observed a decrease in CPUE in four of six most caught, pelagic species. Important environmental variables explaining occurrence and CPUE of the six most caught species in the survey were temperature and Secchi, trawl, and water depths. The trawl survey serves as a valuable long-term monitoring tool to study trends in responses of both native and non-native species to ecosystem changes in Lake Winnipeg.

Late survival of megafauna refuted for Cloggs Cave, SE Australia: Implications for the Australian Late Pleistocene megafauna extinction debate

Understanding of Late Pleistocene megafaunal extinctions in Australia and New Guinea (Sahul) suffers from a paucity of reliably dated bone deposits. Researchers are divided as to when, and why, large-bodied species became extinct. Critical to these interpretations are so-called ‘late survivors’, megafauna that are thought to have persisted for tens of thousands of years after the arrival of people. While the original dating of most sites with purported late survivors has been shown to have been erroneous or problematic, one site continues to feature: Cloggs Cave. Here we report new results that show that Cloggs Cave’s youngest megafauna were deposited in sediments that date to 44,500–54,160 years ago, more than 10,000 years older than previously thought, bringing them into chronological alignment with the emerging continental pattern of megafaunal extinctions. Our results indicate that the youngest megafauna specimens excavated from Cloggs Cave datedate to well before the Last Glacial Maximum (LGM), and their demise could not have been driven by climate change leading into the LGM, the peak of the last Ice Age.

Fuel loads of Neotropical migrant songbirds on autumn passage through the Darién region of Colombia: Influence of migratory distance, route, ENSO, age and body size

AbstractAvailable energy stores determine stopover length, migration speed and likely survival in migrating birds. We measured energy stores by estimating fuel load in 11 species of Neotropical migrant songbirds in the Darién of Colombia over five years. We evaluated 1) whether individuals flying further from breeding origin arrived with smaller fuel loads, 2) if the ENSO (El Niño-Southern Oscillation) cycle affected fuel load and 3) if species known to migrate mostly overwater arrived with less fuel relative to those migrating overland. Breeding origin, inferred from feather δ2H values, only had a significant positive effect on fuel load in Swainson’s Thrush (Catharus ustulatus). Veery (Catharus fuscescens) and Swainson’s thrush had higher and lower fuel loads, respectively, in El Niño years. Multi-species mixed-effects models revealed support for larger fuel loads in larger-bodied species and in species taking overwater routes, contrary to our prediction. Across species, we found no support for common effects of breeding origin or ENSO on fuel loads, in contrast to community-wide effects of migration route and body-size. In general, the variables considered here explained little of the variance in fuel loads, suggesting that inter-individual differences likely have a greater impact than broad-scale factors in our study system.

Exotic species are perceived more than native ones in a megadiverse country as brazil.

Research on environmental perception is essential for the understanding of individuals' relations and expectations towards natural environments. Here, we evaluated the perception of high school students on exotic and native species in Brazil. We interviewed 371 students from two high schools located in the state of Goiás, one with and one without a protected area within its premises. Students needed to identify native and exotic species and to indicate species origin. We used a t-test to evaluate differences between students' scores regarding the correctness of species origin and also ANOVA to assess whether these scores varied among taxonomic groups. Students identified exotic species better than native ones. Students better identified exotic mammals, fishes, and birds than native ones. We found there were no significant relationships of students' knowledge of species' origins with socioecological factors. Students' perceptions of exotic and native species were low and focused on charismatic large-bodied species. We suggest that students are encouraged to expand their knowledge of local biodiversity. Teachers, local schools, and policymakers are essential to achieve this aim. A more diverse methodology for teaching, including new technologies and citizen-science projects, can help establish a genuine interest of local biodiversity students.

Comparative Reproductive Allometry of Syntopic Black-Knobbed Sawbacks (Graptemys nigrinoda) and Alabama Map Turtles (Graptemys pulchra) in the Alabama River, with Comparison to Three Congeners

In many freshwater turtle species, increasing adult female body size is accompanied by increases in both clutch size and egg size. Because clutch size and egg size represent competing sinks for the increasing abdominal space that can be devoted to reproductive potential as a female grows larger, both are hypoallometrically related to body size, i.e., each increases at less than the rate at which body size is increasing. I studied the reproductive allometry of 2 species of the map turtle and sawback genus (Emydidae: Graptemys) in syntopy in the Alabama River. Relative to congeners, Graptemys nigrinoda is a small-bodied species and Graptemys pulchra is a large-bodied species. In the study populations, adult female G. pulchra were on average 23% larger in plastron length and 125% larger in body mass and there was no overlap in size. Both species had positive but hypoallometric relationships of both clutch size and egg size with body size, a pattern reported for 3 congeners previously, thus further demonstrating the competing sinks of increases in both variables and refuting the optimal egg size hypothesis. For interspecific comparisons using analysis of covariance, there was no significant effect of species on clutch size after accounting for the effect of plastron length. The effect of species on egg width and width of the pelvic aperture was significant, with G. pulchra having relatively wider eggs and pelvic apertures, perhaps related to the more domed carapace and larger body sizes of their hatchlings. Compared with 3 congeners, the 2 Alabama River species had relatively small clutches of relatively large eggs. Latitudinal effects on reproductive output may be important in Graptemys, with more-northerly populations tending toward larger clutches of smaller eggs. There is a need to analyze more data from more populations with log-log analyses of reproductive allometry to confirm the trend. There is also a need to consider shape allometry in future analyses; in particular, the hypoallometry of both shell height and shell width relative to shell length.

Native and non-native sources of carbohydrate correlate with abundance of an invasive ant

Invasive species threaten many ecological communities and predicting which communities and sites are invasible remains a key goal of invasion ecology. Although invasive ants often reach high abundances in association with plant-based carbohydrate resources, the source and provenance of these resources are rarely investigated. We characterized carbohydrate resources across ten sites with a range of yellow crazy ant abundance in Arnhem Land, Australia and New Caledonia to determine whether yellow crazy ant (Anoplolepis gracilipes) abundance and trophic position correlate with carbohydrate availability, as well as the relative importance of native and non-native sources of carbohydrates to ant diet. In both locations, measures of yellow crazy ant abundance strongly positively correlated with carbohydrate availability, particularly honeydew production, the number of tended hemipterans, and the number of plants with tended hemipterans. In Arnhem Land, 99.6% of honeydew came from native species, whereas in New Caledonia, only 0.2% of honeydew was produced by a native hemipteran. More honeydew was available in Australia due to three common large-bodied species of Auchenorrhyncha honeydew producers (treehoppers and leafhoppers). Yellow crazy ant trophic position declined with increasing yellow crazy ant abundance indicating that in greater densities the ants are obtaining more of their diet from plant-derived resources, including honeydew and extrafloral nectar. The relationships between yellow crazy ant abundance and carbohydrate availability could not be explained by any of the key environmental variables we measured at our study sites. Our results demonstrate that the positive correlation between yellow crazy ant abundance and honeydew production is not contingent upon the provenance of the hemipterans. Native sources of carbohydrate may play an underappreciated role in greatly increasing community invasibility by ants.

TERT promoter alterations could provide a solution for Peto\u2019s paradox in rodents

Cancer is a genetic disease caused by changes in gene expression resulting from somatic mutations and epigenetic changes. Although the probability of mutations is proportional with cell number and replication cycles, large bodied species do not develop cancer more frequently than smaller ones. This notion is known as Peto’s paradox, and assumes stronger tumor suppression in larger animals. One of the possible tumor suppressor mechanisms involved could be replicative senescence caused by telomere shortening in the absence of telomerase activity. We analysed telomerase promoter activity and transcription factor binding in mammals to identify the key element of telomerase gene inactivation. We found that the GABPA transcription factor plays a key role in TERT regulation in somatic cells of small rodents, but its binding site is absent in larger beavers. Protein binding and reporter gene assays verify different use of this site in different species. The presence or absence of the GABPA TF site in TERT promoters of rodents correlates with TERT promoter activity; thus it could determine whether replicative senescence plays a tumor suppressor role in these species, which could be in direct relation with body mass. The GABPA TF binding sites that contribute to TERT activity in somatic cells of rodents are analogous to those mutated in human tumors, which activate telomerase by a non-ALT mechanism.

Poorly Vetted Conservation Ranks Can Be More Wrong Than Right: Lessons from Texas Land Snails

Setting priorities for scarce conservation dollars requires an accurate accounting of the most vulnerable species. For many invertebrates, lack of taxonomic expertise, low detectability, and funding limitations are impediments to this goal, with conservation ranks usually based on expert opinion, the published literature, and museum records. Because of biases and inaccuracies in these data, they may not provide an accurate basis for conservation ranks, especially when compared to de novo field surveys. We assessed this issue by comparative examination of these data sources in re-ranking the conservation status of all 254 land snail taxa reported from Texas, USA. We confirmed 198 land snail taxa, including 34 new state records. Our assessment of the entire land snail fauna of Texas resulted in (1) a near doubling of recommended Species of Greatest Conservation Need (SGCN) and (2) a 79% turnover in the makeup of SGCN taxa. Field sampling strongly outperformed museum and literature data in the encounter rate of both the entire fauna and all SGCN species, with the latter two demonstrating bias toward larger-bodied species. As a result, conservation priorities based solely on expert opinion and museum and literature records may be more wrong than right, with taxon-appropriate, targeted sampling required to generate accurate rankings.

Conservation status of the southernmost reef of the Amazon Reef System: the Parcel de Manuel Luís

The Parcel de Manuel Luis (PML) is located at the southern end of the Amazon Reef System, which comprises the northernmost reef formations of the Brazilian biogeographical province. Its unique position and singular seascape make the PML an important stepping-stone for marine organisms between the Brazilian and Caribbean provinces. Yet, due to its distance from the shore, high tidal amplitude, and strong currents associated with a series of pinnacles exposed during low spring tides, the PML is one of the least studied reefs in the Western South Atlantic. Here, we integrated sessile benthic community data, fish assemblage surveys, and remote filming of fish interactions to establish the most complete community assessment of the PML reefs to date. In our surveys, we documented 78 sessile benthic taxa, with a taxonomic dominance of macroalgae (54 taxa), including two new occurrences of sponges for the North Brazilian Shelf, as well as four endemic species, such as the fire coral Millepora laboreli. The fish assemblage comprised 59 reef fish species, with biomass dominated mainly by large carnivorous species (e.g., groupers and snappers). Intra- and interspecific interactions were dominated by herbivorous fishes, particularly underpinned by grazing behavior and chasing by territorial species. The considerably high biomass and large-bodied species found in our surveys is rarely seen elsewhere in the Western South Atlantic, suggesting a low level of fishing compared to most other places, and only a few changes were observed in the fish assemblages since the first assessment made in 1998. We also highlight the usefulness of an integrated approach for continued assessment of Western South Atlantic reefs, particularly given emerging threats from mining and oil exploration, and the heavy traffic of commercial vessels in the region. Our findings support the PML as an area of critical conservation interest for reef systems, emphasizing the need for continued enforcement of this marine protected area and its integration in long-term plans of offshore oil and gas development projects.

A scalable, satellite-transmitted data product for monitoring high-activity events in mobile aquatic animals

A growing number of studies are using accelerometers to examine activity level patterns in aquatic animals. However, given the amount of data generated from accelerometers, most of these studies use loggers that archive acceleration data, thus requiring physical recovery of the loggers or acoustic transmission from within a receiver array to obtain the data. These limitations have restricted the duration of tracking (ranging from hours to days) and/or type of species studied (e.g., relatively sessile species or those returning to predictable areas). To address these logistical challenges, we present and test a satellite-transmitted metric for the remote monitoring of changes in activity, measured via a pop-off satellite archival tag (PSAT) with an integrated accelerometer. Along with depth, temperature, and irradiance for geolocation, the PSAT transmits activity data as a time-series (ATS) with a user-programmable resolution. ATS is a count of high-activity events, relative to overall activity/mobility during a summary period. An algorithm is used to identify the high-activity events from accelerometer data and reports the data as a count per time-series interval. Summary statistics describing the data used to identify high-activity events accompany the activity time-series. In this study, we first tested the ATS activity metric through simulating PSAT output from accelerometer data logger archives, comparing ATS to vectorial dynamic body acceleration. Next, we deployed PSATs with ATS under captive conditions with cobia (Rachycentron canadum). Lastly, we deployed seven pop-off satellite archival tags (PSATs) able to collect and transmit ATS in the wild on adult sandbar sharks (Carcharhinus plumbeus). In the captive trials, we identified both resting and non-resting behavior for species and used logistic regression to compare ATS values with observed activity levels. In captive cobia, ATS was a significant predictor of observed activity levels. For 30-day wild deployments on sandbar sharks, satellites received 57.4–73.2% of the transmitted activity data. Of these ATS datapoints, between 21.9 and 41.2% of records had a concurrent set of temperature, depth, and light measurements. These results suggest that ATS is a practical metric for remotely monitoring and transmitting relative high-activity data in large-bodied aquatic species with variable activity levels, under changing environmental conditions, and across broad spatiotemporal scales.

Before, during and after megafaunal extinctions: Human impact on Pleistocene-Holocene trophic networks in South Patagonia

Worldwide extinctions of large terrestrial vertebrates in the late Pleistocene provide insight on how humans reshape ecological communities. Understanding the ecological causes and consequences of megafaunal extinctions requires integrating approaches to reconstruct the ecological communities from the past. Here, we combined archeological and paleontological evidence with network analyses to understand the changes in ecological communities from late Pleistocene to the Holocene in South Patagonia, the last continental region where the encounter between humans and extinct megafauna occurred. The zooarcheological record suggests humans would have interacted mainly with large-bodied species, which comprise a small subset of the available prey. Accordingly, using network reconstructions and structural analyses, we found that human arrival would have produced minor changes in the overall structure of trophic networks. However, those few novel interactions established by humans would have created multiple indirect paths among megafaunal species. Indirect paths are the route for indirect effects such as competition and increase the vulnerability of interaction networks to perturbations. After the extinctions of most of the megafauna, the impoverished network became structurally simpler and densely connected. Our reconstructions of past trophic networks show that multiple indirect effects, potentially contributing to extinctions, can emerge even from a limited number of novel interactions and illustrate how network organization can affect and be affected by extinctions events.

Anthropogenic factors disproportionately affect the occurrence and potential population connectivity of the Neotropic’s apex predator: The jaguar at the southwestern extent of its distribution

Maintaining population connectivity is an important component of jaguar (Panthera onca) conservation. However, the effectiveness of connectivity corridors can be affected by anthropogenic factors. At the southwestern limit of the jaguar’s current distribution in the Yungas and Dry Chaco ecoregions, connectivity among jaguar populations has been compromised by extensive deforestation. The extent that jaguars and their prey are using corridors in the region, and the factors that determine their use, however, has not been evaluated. We sampled 105 sites in 7 study areas in connectivity corridors in the Yungas and Dry Chaco ecoregions of Argentina, Bolivia, and Paraguay for jaguars and six large-bodied principal prey species through interviews with inhabitants and land owners. Using a multi-species community occupancy modeling framework, we examined species occurrence in relation to forest cover and anthropogenic factors. All species were positively associated with increasing forest cover, decreasing number of homesteads, and increasing distance from roads and settlements, with jaguar occurrence most strongly negatively correlated with anthropogenic factors. Mean conditional occupancy of jaguars was high (>75%) in only two study areas, while only two study areas had mean conditional occupancy estimates of jaguars that were consistent with prey occurrence, with other sites having lower jaguar occurrence than expected. Despite high levels of forest cover and sufficient prey availability, the lower than expected jaguar occurrence in most study areas suggests that illegal killing is likely a principal factor determining jaguar occurrence. The probability of site use by jaguars in most study areas was low, and consequently, functional connectivity is reduced in those areas and likely throughout the region. Our findings have range-wide implications for jaguar conservation since we show that despite sufficient habitat and prey availability, jaguar populations are likely reduced or extirpated by illegal killing driven by jaguar-ranching conflict, cultural norms, or fear.

Nest‐Box Use by Wood Ducks and Black‐Bellied Whistling Ducks in Coastal South Carolina

ABSTRACTWe surveyed nest‐structure use by sympatric nesting wood ducks (Aix sponsa) and black‐bellied whistling ducks (Dendrocygna autumnalis) across coastal South Carolina, USA, in 2016–2017. Of 718 nest boxes surveyed cumulatively in 2016 and 2017, 61% were used by wood ducks and 15% by black‐bellied whistling ducks. Lower nest‐box use by whistling ducks was related to recent arrivals and breeding by the species in South Carolina. Nest‐box use by wood ducks was 6% greater for every 1,000‐cm3 decrease from the mean internal box volume of all boxes monitored, whereas use by black‐bellied whistling ducks was 20% greater for every 1,000‐cm3 increase from the mean internal volume of all boxes. Box use was 15% and 11% greater by wood ducks and black‐bellied whistling ducks, respectively, for every 10% decrease from the mean percent canopy cover of all nest boxes. Nest‐box use by black‐bellied whistling ducks was 18% and 10% greater for every 10‐cm increase from the mean distance from the base of a box's entrance vertically to the ground or water and every 10‐m decrease from the mean distance to the nearest box for all boxes monitored, respectively. Our results suggested nest boxes with internal volumes of ~15,000–31,000 cm3 were most used by wood ducks, but the conventional nest box with an internal volume of 34,375 cm3 and internal dimensions of 25 × 25 × 55 cm accommodated wood ducks and black‐bellied whistling ducks, and can be deployed where the species are sympatric. However, where black‐bellied whistling ducks occur, the diameter of an entrance hole for nest boxes should be 13 cm to allow passage by the larger bodied species. We suggest a need for research to estimate recruitment rates for box‐nesting females and cost effectiveness of box programs based on female recruitment. © 2020 The Wildlife Society.

Daily Nest Predation Rates Decrease with Body Size in Passerine Birds

AbstractBody size evolution is generally framed by the benefits of being large, while costs are largely overlooked. An important putative cost of being large is the need to extend development periods, which should increase exposure to predation and potentially select against larger size. In birds, this selection pressure can be important because predation is the main source of offspring mortality and predators should more readily detect the larger nests associated with larger body sizes. Here, we show for diverse passerine birds across the world that counter to expectations, larger species suffer lower daily nest predation rates than smaller species. This pattern is consistent despite latitudinal variation in predation and does not seem to reflect a tendency of larger species to use more protected nests or less exposed nest locations. Evidence instead suggests that larger species attack a wider array of predator sizes, which could reduce predation rates in nests of large-bodied species. Regardless of the mechanism, the lower daily nest predation rates of larger species yield slightly lower predation rates over the entire development period compared with smaller species. These results highlight the importance of behavior as a mechanism to alter selection pressures and have implications for body size evolution.

Temporal Dynamics of Fish Assemblages as a Reflection of Policy Shift from Fishing Concession to Co-Management in One of the World’s Largest Tropical Flood Pulse Fisheries

Inland fisheries management in Cambodia has undergone two major policy reforms over the last two decades. These reforms led to the abolishment of a century-old commercial fishing lot system in 2012 and the establishment of new fish sanctuary and community fishing areas. However, the status of fisheries and fish assemblages following the reforms is not well understood. Here, we investigated the temporal changes in fish catch weight and fish assemblage structure for the period 1995–2000 before fishing lot abolishment (BLA) and for the period 2012–2015 after the removal of all fishing lots (after lot abolishment-ALA) using time-series fish catch data recorded from the Tonle Sap Lake (TSL), one of the world largest inland fisheries. We found (i) mean catch trends vary seasonally, with stable catch trends during the BLA and decreasing catch trends during the ALA and (ii) significant shifts in fish assemblage composition, notably a shift from large-bodied, migratory, and/or predatory species during the BLA toward more short-distance migratory and/or floodplain, small-bodied species during the ALA. Fishing lot abolishment coincided with substantial changes to floodplain habitats and increases in fishing pressure, threatening TSL fish stocks. Flow alterations caused by dams and climate change may exacerbate the problem. Therefore, to realize the fisheries reform objectives, it is imperative to strengthen the fisheries’ governance and management system, including effective law enforcement, institutional strengthening, improved planning, cooperation, and coordination as well as clearly defined roles and responsibilities among concerned stakeholders at all levels.

Eruptive dynamics are common in managed mammal populations.

Successful conservation management is often based on the principle that small or declining populations can recover if we identify and remove the factors that caused them to decline in the first place. But what form will that recovery take? Theory tells us that when a strong limiting factor is removed, a population should increase in size to where it becomes limited by some other factor. However, if the subsequent limitation involves feedbacks between the density of a consumer and its resource, there is potential for the consumer population to undergo substantial fluctuations in size that we would characterize as boom-bust or eruptive dynamics. We analysed long-term (7.6-29yr) data documenting changes in the abundance of 169 populations of 20 mammal species released from a strong limiting factor (fox predation) in Australia. We show that many populations (44) exhibited eruptive dynamics, with exponential increase to a peak and subsequent population decline. Of 51 populations showing eruptive dynamics (the Australian populations plus seven translocated ungulate populations), the time taken for erupting populations to reach a peak before declining was related negatively to the intrinsic rate of population growth and positively to body mass, such that larger-bodied species with slow rates of population growth had a longer period of population increase before declining. Our results suggest that a substantial proportion of populations recovering after removal of a threatening process are likely to exhibit eruptive dynamics, and that managers of recovering or translocated populations should anticipate this outcome in conservation planning.

Body size is a good proxy for vertebrate charisma

The charisma of species, i.e., their popularity among people, influences how much we are willing to invest in seeing, studying, and protecting them. Previous studies have investigated the drivers of animal charisma, but because collection of species popularity data is costly in terms of time and resources, these are often restricted to a small number of species, making it difficult to generalize results at a scale useful for macroecological studies. Here, we test the hypothesis that animal charisma scales with species body size using nine open-access datasets on animal charisma for 13,680 species from four vertebrate classes: amphibians, birds, mammals, and reptiles. We performed linear mixed models using all studies taken together and, in supplement, linear models on each study separately. We found that animal charisma scales positively with species body size across different vertebrate classes, geographic areas, and charisma estimation methodologies. This general scaling relationship between body size and animal charisma supports large-bodied species to have disproportionate importance for conservation due to their high appeal on people. These findings suggest that body size can be used as a proxy for the charisma of species at broad spatial scales and for large numbers of species, as an alternative to more resource-intensive surveys.

Site-Level Variation in Parrotfish Grazing and Bioerosion as a Function of Species-Specific Feeding Metrics

Parrotfish provide important ecological functions on coral reefs, including the provision of new settlement space through grazing and the generation of sediment through bioerosion of reef substrate. Estimating these functions at an ecosystem level depends on accurately quantifying the functional impact of individuals, yet parrotfish feeding metrics are only available for a limited range of sites, species and size classes. We quantified bite rates, proportion of bites leaving scars and scar sizes in situ for the dominant excavator (Cetoscarus ocellatus, Chlorurus strongylocephalus, Ch. sordidus) and scraper species (Scarus rubroviolaceus, S. frenatus, S. niger, S. tricolor, S. scaber, S. psittacus) in the central Indian Ocean. This includes the first record of scar frequencies and sizes for the latter three species. Bite rates varied with species and life phase and decreased with body size. The proportion of bites leaving scars and scar sizes differed among species and increased with body size. Species-level allometric relationships between body size and each of these feeding metrics were used to parameterize annual individual grazing and bioerosion rates which increase non-linearly with body size. Large individuals of C. ocellatus, Ch. strongylocephalus and S. rubroviolaceus can graze 200–400 m2 and erode >500 kg of reef substrate annually. Smaller species graze 1–100 m2 yr−1 and erode 0.2–30 kg yr−1. We used these individual functional rates to quantify community grazing and bioerosion levels at 15 sites across the Maldives and the Chagos Archipelago. Although parrotfish density was 2.6 times higher on Maldivian reefs, average grazing (3.9 ± 1.4 m2 m−2 reef yr−1) and bioerosion levels (3.1 ± 1.2 kg m−2 reef yr−1) were about 15% lower than in the Chagos Archipelago (4.5 ± 2.3 and 3.7 ± 3.0, respectively), due to the dominance of small species and individuals in the Maldives (90% <30 cm length). This demonstrates that large-bodied species and individuals contribute disproportionally to both grazing and bioerosion. Across all sites, grazing increased by 66 ± 5 m2 ha−1 and bioerosion by 109 ± 9 kg ha−1 for every kg increase in parrotfish biomass. However, for a given level of parrotfish biomass, grazing and bioerosion levels were higher on Maldivian reefs than in the Chagos Archipelago. This suggests that small-bodied fish assemblages can maintain ecosystem functions, but only if key species are present in sufficiently high numbers.

Extent, intensity and drivers of mammal defaunation: a continental-scale analysis across the Neotropics

Neotropical mammal diversity is currently threatened by several chronic human-induced pressures. We compiled 1,029 contemporary mammal assemblages surveyed across the Neotropics to quantify the continental-scale extent and intensity of defaunation and understand their determinants based on environmental covariates. We calculated a local defaunation index for all assemblages—adjusted by a false-absence ratio—which was examined using structural equation models. We propose a hunting index based on socioenvironmental co-variables that either intensify or inhibit hunting, which we used as an additional predictor of defaunation. Mammal defaunation intensity across the Neotropics on average erased 56.5% of the local source fauna, with ungulates comprising the most ubiquitous losses. The extent of defaunation is widespread, but more incipient in hitherto relatively intact major biomes that are rapidly succumbing to encroaching deforestation frontiers. Assemblage-wide mammal body mass distribution was greatly reduced from a historical 95th-percentile of ~ 14 kg to only ~ 4 kg in modern assemblages. Defaunation and depletion of large-bodied species were primarily driven by hunting pressure and remaining habitat area. Our findings can inform guidelines to design transnational conservation policies to safeguard native vertebrates, and ensure that the “empty ecosystem” syndrome will be deterred from reaching much of the New World tropics.

Sampling understory birds in different habitat types using point counts and camera traps

Point counts are widely used to assess bird diversity. However, this method has some limitations and can be affected by observer bias. For this reason, it is commonly complemented with other methods (e.g., mist-nets, sound recordings). Surprisingly, camera traps are rarely used on birds, despite being a common approach for wildlife monitoring. This approach has many advantages: minimum observer interference, little demanding in the field, cost-effective, and can be operated over large areas and long periods. We contrasted the results of point counts and camera traps along a 450-km transect, comprising four habitat types (old- and second-growth native forests, logged forests, and abandoned forestry plantations). We detected 21 understory bird species using point counts (effectiveness of 91.3%) and 18 species using camera traps (effectiveness of 78.3%). From those, we detected 16 species with both methods. Species richness estimations across habitats were variable when we used point counts, but we found similar results with camera traps. Point counts performed better on large-bodied and conspicuous species, camera traps were less biased towards body size and conspicuousness and performed better than point counts in some cases. Camera traps are a useful approach to assess understory bird diversity, providing similar results than point counts. Furthermore, we can obtain better results if we use both methods simultaneously.