Tropical forests are increasingly degraded by industrial logging, urbanization, agriculture, and infrastructure, with only 20% of the remaining area considered intact. However, this figure does not ...include other, more cryptic but pervasive forms of degradation, such as overhunting. Here, we quantified and mapped the spatial patterns of mammal defaunation in the tropics using a database of 3,281 mammal abundance declines from local hunting studies. We simultaneously accounted for population abundance declines and the probability of local extirpation of a population as a function of several predictors related to human accessibility to remote areas and species' vulnerability to hunting. We estimated an average abundance decline of 13% across all tropical mammal species, with medium-sized species being reduced by >27% and large mammals by >40%. Mammal populations are predicted to be partially defaunated (i.e., declines of 10%-100%) in ca. 50% of the pantropical forest area (14 million km2), with large declines (>70%) in West Africa. According to our projections, 52% of the intact forests (IFs) and 62% of the wilderness areas (WAs) are partially devoid of large mammals, and hunting may affect mammal populations in 20% of protected areas (PAs) in the tropics, particularly in West and Central Africa and Southeast Asia. The pervasive effects of overhunting on tropical mammal populations may have profound ramifications for ecosystem functioning and the livelihoods of wild-meat-dependent communities, and underscore that forest coverage alone is not necessarily indicative of ecosystem intactness. We call for a systematic consideration of hunting effects in (large-scale) biodiversity assessments for more representative estimates of human-induced biodiversity loss.
Seed dispersal is a key process affecting the structure, composition and spatial dynamics of plant populations. Numerous plant species in the tropics rely upon animals to disperse their seeds. Humans ...have altered mammalian movements, which will likely affect seed dispersal distances (SDD). Altered SDD may have a range of consequences for plant communities including reduced seedling recruitment and plant biomass, seed trait homogenization, altered gene flow and a reduced capacity to respond to environmental changes. Therefore, modelling the consequences of altered animal behaviour on ecosystem processes is important for predicting how ecosystems will respond to human impacts. While previous research has focused on the link between animal species extirpation and SDD, it remains unclear how changes in mammalian movement will impact SDD. Here we implemented a mechanistic modelling approach to examine how mammalian movement reductions impact SDD in the tropics. We combined allometric theory with a mechanistic seed dispersal model to estimate SDD via the movement of 37 large frugivorous mammals (> 10 kg) in the tropics under different levels of human footprint, a global proxy of direct and indirect human disturbances. Our results suggest that assemblage‐level SDD reductions are estimated to be up to 80% across the tropics in response to human disturbance. This is particularly the case in areas with high human impact such as agricultural landscapes and suburban areas. The region with the largest reductions in SDD was the Asia‐Pacific with average reductions of 25%, followed by Central–South America (16%) and then Africa (15%). Our study provides insights into how human‐induced changes in movement behaviour of large mammals could translate into altered ecosystem functioning.
Large carnivores can exert top–down effects in ecosystems, but the size of these effects are largely unknown. Empirical investigation on the importance of large carnivores for ecosystem structure and ...functioning presents a number of challenges due to the large spatio‐temporal scale and the complexity of such dynamics. Here, we applied a mechanistic global ecosystem model to investigate the influence of large‐carnivore removal from undisturbed ecosystems. First, we simulated large‐carnivore removal on the global scale to inspect the geographic pattern of top–down control and to disentangle the functional role of large carnivores in top–down control in different environmental contexts. Second, we conducted four small‐scale ecosystem simulation experiments to understand direct and indirect changes in food‐web structure under different environmental conditions. We found that the removal of top–down control exerted by large carnivores (> 21 kg) can trigger large trophic cascades, leading to an overall decrease in autotroph biomass globally. Furthermore, the loss of large carnivores resulted in an increase of mesopredators. The magnitude of these changes was positively related to primary productivity (NPP), in line with the ‘exploitation ecosystem hypothesis’. In addition, we found that seasonality in NPP dampened the magnitude of change following the removal of large carnivores. Our results reinforce the idea that large carnivores play a fundamental role in shaping ecosystems, and further declines and extinctions can trigger substantial ecosystem responses. Our findings also support previous studies suggesting that natural ecosystem dynamics have been severely modified and are still changing as a result of the widespread decline and extinction of large carnivores.
Species distribution models (SDMs) are frequently used to understand the influence of site properties on species occurrence. For robust model inference, SDMs need to account for the spatial ...autocorrelation of virtually all species occurrence data. Current methods do not routinely distinguish between extrinsic and intrinsic drivers of spatial autocorrelation, although these may have different implications for conservation.
Here, we present and test a method that disentangles extrinsic and intrinsic drivers of spatial autocorrelation using repeated observations of a species. We focus on unknown habitat characteristics and conspecific interactions as extrinsic and intrinsic drivers, respectively. We model the former with spatially correlated random effects and the latter with an autocovariate, such that the spatially correlated random effects are constant across the repeated observations whereas the autocovariate may change. We tested the performance of our model on virtual species data and applied it to observations of the corncrake Crex crex in the Netherlands.
Applying our model to virtual species data revealed that it was well able to distinguish between the two different drivers of spatial autocorrelation, outperforming models with no or a single component for spatial autocorrelation. This finding was independent of the direction of the conspecific interactions (i.e. conspecific attraction versus competitive exclusion). The simulations confirmed that the ability of our model to disentangle both drivers of autocorrelation depends on repeated observations. In the case study, we discovered that the corncrake has a stronger response to habitat characteristics compared to a model that did not include spatially correlated random effects, whereas conspecific interactions appeared to be less important. This implies that future conservation efforts should primarily focus on maximizing habitat availability.
Our study shows how to systematically disentangle extrinsic and intrinsic drivers of spatial autocorrelation. The method we propose can help to correctly identify the main drivers of species distributions.
Human population and economic growth have resulted in roads transecting much of the North American landscape and this has negatively affected wildlife populations by fragmenting habitat, impeding ...movement between populations and increasing the chance of wildlife‐vehicle collisions. A common conservation tool to counteract these effects is the incorporation of road mitigation structures (RMS, i.e., jumpouts and overpasses/underpasses/fencing) into highway systems. However, gaps remain in our knowledge on RMS efficacy due to a lack of long‐term multispecies studies that can assess temporal and species‐specific variation in use. We investigate the efficacy of the Alberta Environment and Parks and Alberta Transportation RMS on the Trans‐Canada Highway (TCH) in the Bow Valley by analyzing annual reported wildlife‐vehicle collisions over a 23‐year period and wildlife use of the underpasses over a ten‐year period. We found that the incorporation of multiple underpasses and jumpouts, along with fencing, reduced the number of reported wildlife‐vehicle collisions on the TCH. We also found that wildlife use of the RMS exhibited variation with regards to month and location. Overall, our results add to the research supporting RMS effectiveness and suggest that incorporating additional similar infrastructure has the potential to further reduce wildlife‐vehicle collisions on the TCH.
A common conservation tool to mitigate for fragmenting habitat, impeding movement between populations, and wildlife‐vehicle collisions is the incorporation of road mitigation structures (i.e., jumpouts and over/underpasses and fencing) into highway systems. In this study, we found in the long‐term that the incorporation of multiple underpasses and jumpouts, along with fencing reduced the number of wildlife‐vehicle collisions on the Trans‐Canada Highway.
The social environment in which individuals live affects their fitness and in turn population dynamics as a whole. Birds with facultative cooperative breeding can live in social groups with ...dominants, subordinate helpers that assist with the breeding of others, and subordinate non‐helpers. Helping behaviour benefits dominants through increased reproductive rates and reduced extrinsic mortality, such that cooperative breeding might have evolved in response to unpredictable, harsh conditions affecting reproduction and/or survival of the dominants. Additionally, there may be different costs and benefits to both helpers and non‐helpers, depending on the time‐scale. For example, early‐life costs might be compensated by later‐life benefits. These differential effects are rarely analysed in the same study.
We examined whether helping behaviour affects population persistence in a stochastic environment and whether there are direct fitness consequences of different life‐history tactics adopted by helpers and non‐helpers.
We parameterised a matrix population model describing the population dynamics of female Seychelles warblers Acrocephalus sechellensis, birds that display facultative cooperative breeding. The stochastic density‐dependent model is defined by a (st)age structure that includes life‐history differences between helpers and non‐helpers and thus can estimate the demographic mechanisms of direct benefits of helping behaviour.
We found that population dynamics are strongly influenced by stochastic variation in the reproductive rates of the dominants, that helping behaviour promotes population persistence and that there are only early‐life differences in the direct fitness of helpers and non‐helpers.
Through a matrix population model, we captured multiple demographic rates simultaneously and analysed their relative importance in determining population dynamics of these cooperative breeders. Disentangling early‐life versus lifetime effects of individual tactics sheds new light on the costs and benefits of helping behaviour. For example, the finding that helpers and non‐helpers have similar lifetime reproductive outputs and that differences in reproductive values between the two life‐history tactics arise only in early life suggests that overall, helpers and non‐helpers have a similar balance of costs and benefits when analysing direct benefits. We recommend analysing the consequence of different life‐history tactics, during both early life and over the lifetime, as analyses of these different time frames may produce conflicting results.
Cooperative breeding is widespread among passerine birds. Yet, the impact of environmental stochasticity on their population dynamics is poorly known. The authors looked at the Seychelles warblers (Acrocephalus sechellensis) as a case study. Helping behaviour had a positive effect on population dynamics because it could buffer fluctuations in reproductive success. Image credit: L. Lopera Doblas.
Abstract
Even in well-studied organisms, it is often challenging to uncover the social and environmental determinants of fitness. Typically, fitness is determined by a variety of factors that act in ...concert, thus forming complex networks of causal relationships. Moreover, even strong correlations between social and environmental conditions and fitness components may not be indicative of direct causal links, as the measured variables may be driven by unmeasured (or unmeasurable) causal factors. Standard statistical approaches, like multiple regression analyses, are not suited for disentangling such complex causal relationships. Here, we apply structural equation modeling (SEM), a technique that is specifically designed to reveal causal relationships between variables, and which also allows to include hypothetical causal factors. Therefore, SEM seems ideally suited for comparing alternative hypotheses on how fitness differences arise from differences in social and environmental factors. We apply SEM to a rich data set collected in a long-term study on the Seychelles warbler (Acrocephalus sechellensis), a bird species with facultatively cooperative breeding and a high rate of extra-group paternity. Our analysis reveals that the presence of helpers has a positive effect on the reproductive output of both female and male breeders. In contrast, per capita food availability does not affect reproductive output. Our analysis does not confirm earlier suggestions on other species that the presence of helpers has a negative effect on the reproductive output of male breeders. As such, both female and male breeders should tolerate helpers in their territories, irrespective of food availability.
In cooperatively breeding birds, non-parental individuals help the breeding pair with raising the young. As helpers can also have negative effects, it is not clear whether and when the breeding pair should tolerate them. We show that a statistical method (causal analysis) can shed new light on this issue. Analyzing data on Seychelles warblers, we show that reproductive success is not affected by food availability, but that both breeders profit from the presence of helpers.
Purpose
To investigate whether COVID-19-ARDS differs from all-cause ARDS.
Methods
Thirty-two consecutive, mechanically ventilated COVID-19-ARDS patients were compared to two historical ARDS ...sub-populations 1:1 matched for PaO
2
/FiO
2
or for compliance of the respiratory system. Gas exchange, hemodynamics and respiratory mechanics were recorded at 5 and 15 cmH
2
O PEEP. CT scan variables were measured at 5 cmH
2
O PEEP.
Results
Anthropometric characteristics were similar in COVID-19-ARDS, PaO
2
/FiO
2
-matched-ARDS and Compliance-matched-ARDS. The PaO
2
/FiO
2
-matched-ARDS and COVID-19-ARDS populations (both with PaO
2
/FiO
2
106 ± 59 mmHg) had different respiratory system compliances (Crs) (39 ± 11 vs 49.9 ± 15.4 ml/cmH
2
O,
p
= 0.03). The Compliance-matched-ARDS and COVID-19-ARDS had similar Crs (50.1 ± 15.7 and 49.9 ± 15.4 ml/cmH
2
O, respectively) but significantly lower PaO
2
/FiO
2
for the same Crs (160 ± 62 vs 106.5 ± 59.6 mmHg,
p
< 0.001). The three populations had similar lung weights but COVID-19-ARDS had significantly higher lung gas volume (PaO
2
/FiO
2
-matched-ARDS 930 ± 644 ml, COVID-19-ARDS 1670 ± 791 ml and Compliance-matched-ARDS 1301 ± 627 ml,
p
< 0.05). The venous admixture was significantly related to the non-aerated tissue in PaO
2
/FiO
2
-matched-ARDS and Compliance-matched-ARDS (
p
< 0.001) but unrelated in COVID-19-ARDS (
p
= 0.75), suggesting that hypoxemia was not only due to the extent of non-aerated tissue. Increasing PEEP from 5 to 15 cmH
2
O improved oxygenation in all groups. However, while lung mechanics and dead space improved in PaO
2
/FiO
2
-matched-ARDS, suggesting recruitment as primary mechanism, they remained unmodified or worsened in COVID-19-ARDS and Compliance-matched-ARDS, suggesting lower recruitment potential and/or blood flow redistribution.
Conclusions
COVID-19-ARDS is a subset of ARDS characterized overall by higher compliance and lung gas volume for a given PaO
2
/FiO
2
, at least when considered within the timeframe of our study.
Purpose
This study aimed at investigating the mechanisms underlying the oxygenation response to proning and recruitment maneuvers in coronavirus disease 2019 (COVID-19) pneumonia.
Methods
Twenty-five ...patients with COVID-19 pneumonia, at variable times since admission (from 1 to 3 weeks), underwent computed tomography (CT) lung scans, gas-exchange and lung-mechanics measurement in supine and prone positions at 5 cmH
2
O and during recruiting maneuver (supine, 35 cmH
2
O). Within the non-aerated tissue, we differentiated the atelectatic and consolidated tissue (recruitable and non-recruitable at 35 cmH
2
O of airway pressure). Positive/negative response to proning/recruitment was defined as increase/decrease of PaO
2
/FiO
2
. Apparent perfusion ratio was computed as venous admixture/non aerated tissue fraction.
Results
The average values of venous admixture and PaO
2
/FiO
2
ratio were similar in supine-5 and prone-5. However, the PaO
2
/FiO
2
changes (increasing in 65% of the patients and decreasing in 35%, from supine to prone) correlated with the balance between resolution of dorsal atelectasis and formation of ventral atelectasis (
p
= 0.002). Dorsal consolidated tissue determined this balance, being inversely related with dorsal recruitment (
p
= 0.012). From supine-5 to supine-35, the apparent perfusion ratio increased from 1.38 ± 0.71 to 2.15 ± 1.15 (
p
= 0.004) while PaO
2
/FiO
2
ratio increased in 52% and decreased in 48% of patients. Non-responders had consolidated tissue fraction of 0.27 ± 0.1 vs. 0.18 ± 0.1 in the responding cohort (
p
= 0.04). Consolidated tissue, PaCO
2
and respiratory system elastance were higher in patients assessed late (all
p
< 0.05), suggesting, all together, “fibrotic-like” changes of the lung over time.
Conclusion
The amount of consolidated tissue was higher in patients assessed during the third week and determined the oxygenation responses following pronation and recruitment maneuvers.
COVID-19 infection may lead to acute respiratory distress syndrome (CARDS) where severe gas exchange derangements may be associated, at least in the early stages, only with minor pulmonary ...infiltrates. This may suggest that the shunt associated to the gasless lung parenchyma is not sufficient to explain CARDS hypoxemia. We designed an algorithm (Vent
Q
), based on the same conceptual grounds described by J.B. West in 1969. We set 498 ventilation-perfusion (V
/Q) compartments and, after calculating their blood composition (PO
, PCO
, and pH), we randomly chose 10
combinations of five parameters controlling a bimodal distribution of blood flow. The solutions were accepted if the predicted PaO
and PaCO
were within 10% of the patient's values. We assumed that the shunt fraction equaled the fraction of non-aerated lung tissue at the CT quantitative analysis. Five critically-ill patients later deceased were studied. The PaO
/FiO
was 91.1 ± 18.6 mmHg and PaCO
69.0 ± 16.1 mmHg. Cardiac output was 9.58 ± 0.99 L/min. The fraction of non-aerated tissue was 0.33 ± 0.06. The model showed that a large fraction of the blood flow was likely distributed in regions with very low V
/Q (Q
= 0.06 ± 0.02) and a smaller fraction in regions with moderately high V
/Q. Overall LogSD, Q was 1.66 ± 0.14, suggestive of high V
/Q inequality. Our data suggest that shunt alone cannot completely account for the observed hypoxemia and a significant V
/Q inequality must be present in COVID-19. The high cardiac output and the extensive microthrombosis later found in the autopsy further support the hypothesis of a pathological perfusion of non/poorly ventilated lung tissue.
Hypothesizing that the non-aerated lung fraction as evaluated by the quantitative analysis of the lung computed tomography (CT) equals shunt (V
/Q = 0), we used a computational approach to estimate the magnitude of the ventilation-perfusion inequality in severe COVID-19. The results show that a severe hyperperfusion of poorly ventilated lung region is likely the cause of the observed hypoxemia. The extensive microthrombosis or abnormal vasodilation of the pulmonary circulation may represent the pathophysiological mechanism of such V
/Q distribution.
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