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Environment, Ecology & Earth's biodiversity

United Kingdom Sully Offline
Ecology & Rewilding
*****
#46

I had wondered for a while why equatorial africa had both forest and savannah biomes. This interesting paper sheds some light on why that is.

Floristic evidence for alternative biome states in tropical Africa

Abstract

The idea that tropical forest and savanna are alternative states is crucial to how we manage these biomes and predict their future under global change. Large-scale empirical evidence for alternative stable states is limited, however, and comes mostly from the multimodal distribution of structural aspects of vegetation. These approaches have been criticized, as structure alone cannot separate out wetter savannas from drier forests for example, and there are also technical challenges to mapping vegetation structure in unbiased ways. Here, we develop an alternative approach to delimit the climatic envelope of the two biomes in Africa using tree species lists gathered for a large number of forest and savanna sites distributed across the continent. Our analyses confirm extensive climatic overlap of forest and savanna, supporting the alternative stable states hypothesis for Africa, and this result is corroborated by paleoecological evidence. Further, we find the two biomes to have highly divergent tree species compositions and to represent alternative compositional states. This allowed us to classify tree species as forest vs. savanna specialists, with some generalist species that span both biomes. In conjunction with georeferenced herbarium records, we mapped the forest and savanna distributions across Africa and quantified their environmental limits, which are primarily related to precipitation and seasonality, with a secondary contribution of fire. These results are important for the ongoing efforts to restore African ecosystems, which depend on accurate biome maps to set appropriate targets for the restored states but also provide empirical evidence for broad-scale bistability.
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United Kingdom Sully Offline
Ecology & Rewilding
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#47

What factors increase the vulnerability of native birds to the impacts of alien birds?

Abstract

Biodiversity impacts caused by alien species can be severe, including those caused by alien birds. In order to protect native birds, we aimed to identify factors that influence their vulnerability to the impacts of alien birds. We first reviewed the literature to identify native bird species sustaining such impacts. We then assigned impact severity scores to each native bird species, depending on the severity of the impacts sustained, and performed two types of analyses. First, we used contingency table tests to examine the distribution of impacts across their severity, type and location, and across native bird orders. Second, we used mixed-effects models to test factors hypothesised to influence the vulnerability of native birds to the impacts of alien birds.
Ground-nesting shorebirds and seabirds were more prone to impacts through predation, while cavity-nesting woodpeckers and parrots were more prone to impacts through competition. Native bird species were more vulnerable when they occupied islands, warm regions, regions with climatic conditions similar to those in the native range of the invading alien species, and when they were physically smaller than the invading alien species. To a lesser extent, they were also vulnerable when they shared habitat preferences with the invading alien species.
By considering the number and type of native bird species affected by alien birds, we demonstrate predation impacts to be more widespread than previously indicated, but also that damaging predation impacts may be underreported. We identify vulnerable orders of native birds, which may require conservation interventions; characteristics of native birds that increase their vulnerability, which may be used to inform risk assessments; and regions where native birds are most vulnerable, which may direct management interventions. The impacts sustained by native birds may be going unnoticed in many regions of the world: there is a clear need to identify and manage them.
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United Kingdom Sully Offline
Ecology & Rewilding
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#48

The presence of a larger carnivore, regardless of how much of a threat they actually pose, elicits a uniform avoidance response in pine martens.

The best defence is not being there: avoidance of larger carnivores is not driven by risk intensity

Abstract

Species interactions are key factors determining the distribution and structure of species assemblages. Owing to their central positions, mid-ranking mammalian carnivores are involved in interactions with numerous species, including competition for resources and instances of killing by higher ranking predators. Lethal interactions can directly influence species’ demography. However, the fear of lethal interactions, competition or both may also affect when and where individuals are active (i.e. non-lethal interactions). Although differences in body–size and trophic overlap are known predictors of the frequency of lethal interactions, their influence on non-lethal interactions is uncertain. Through camera trapping, we studied non-lethal interactions between a small mesocarnivore (pine marten), a potential killer and intense competitor (red fox) and a moderate competitor and unlikely killer (Eurasian badger). We determined overlap and differences in their diel activity patterns and the degree of spatial overlap in two seasons with contrasting resource availability. Additionally, we estimated the effect of larger carnivore detection rates on pine marten detection rates. We also compared time intervals between pine marten visits to baited stations in the absence and presence of either or both larger carnivores. Our results are consistent with pine martens distributing their daily activity to maximize overlap with prey and to minimize competition and risk of aggression over the spatial scale. Pine martens also responded to the immediate threat of larger carnivores irrespective of the threat they pose by taking 4–7 days longer to re-visit a station. Small-scale non-lethal interactions such as these may enable pine martens to coexist closely with two larger carnivores, yet it remains uncertain whether their population incurs a demographic cost through restricted access to resources. Carnivore's risk-avoidance strategies could be harnessed to protect prey species of interest. However, our results suggest avoidance is short-lived and recurrent stimuli would be necessary.
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United Kingdom Sully Offline
Ecology & Rewilding
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#49

"Even in the Serengeti, where megaherbivores would seemingly overwhelm any impact by insect herbivores, the amount of tissue eaten by the two classes is essentially equal (Sinclair 1975)."

From the book:
Trophic Cascades: Predators, Prey, and the Changing Dynamics of Nature
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United Kingdom Sully Offline
Ecology & Rewilding
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#50

Outsized effect of predation: Wolves alter wetland creation and recolonization by killing ecosystem engineers

Abstract

Gray wolves are a premier example of how predators can transform ecosystems through trophic cascades. However, whether wolves change ecosystems as drastically as previously suggested has been increasingly questioned. We demonstrate how wolves alter wetland creation and recolonization by killing dispersing beavers. Beavers are ecosystem engineers that generate most wetland creation throughout boreal ecosystems. By studying beaver pond creation and recolonization patterns coupled with wolf predation on beavers, we determined that 84% of newly created and recolonized beaver ponds remained occupied until the fall, whereas 0% of newly created and recolonized ponds remained active after a wolf killed the dispersing beaver that colonized that pond. By affecting where and when beavers engineer ecosystems, wolves alter all of the ecological processes (e.g., water storage, nutrient cycling, and forest succession) that occur due to beaver-created impoundments. Our study demonstrates how predators have an outsized effect on ecosystems when they kill ecosystem engineers.
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United Kingdom Sully Offline
Ecology & Rewilding
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#51

Biotic interactions are more often important at species’ warm versus cool range edges

Abstract

Predicting which ecological factors constrain species distributions is a fundamental ecological question and critical to forecasting geographic responses to global change. Darwin hypothesised that abiotic factors generally impose species’ high-latitude and high-elevation (typically cool) range limits, whereas biotic interactions more often impose species’ low-latitude/low-elevation (typically warm) limits, but empirical support has been mixed. Here, we clarify three predictions arising from Darwin's hypothesis and show that previously mixed support is partially due to researchers testing different predictions. Using a comprehensive literature review (885 range limits), we find that biotic interactions, including competition, predation and parasitism, contributed to >60% of range limits and influenced species’ warm limits more often than cool limits. Abiotic factors contributed more often than biotic interactions to cool range limits, but temperature contributed frequently to both cool and warm limits. Our results suggest that most range limits will be sensitive to climate warming, but warm-limit responses in particular will depend strongly on biotic interactions.
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United Kingdom Sully Offline
Ecology & Rewilding
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#52

Large wild herbivores slow down the rapid decline of plant diversity in a tropical forest biodiversity hotspot

Abstract

  1. The UN declaration of the Decade of Ecosystem Restoration 2021–2030 emphasizes the need for effective measures to restore ecosystems and safeguard biodiversity. Large herbivores regulate many ecosystem processes and functions; yet, their potential as a nature-based solution to buffer against long-term temporal declines in biodiversity associated with global change and restore diversity in secondary forests remains unknown.
  2. By means of an exclusion experiment, we tested experimentally the buffering effects of large wild herbivores to avert against long-term biodiversity collapse in old-growth and secondary tropical forests in the Atlantic Forest of Brazil where sapling abundance and species richness declined c. 20% over the course of 10 years. The experiment comprised 50 large herbivore exclosure-open control plot pairs (25 at the old-growth forest and 25 at the secondary forest), where 2 m2 were monitored in every plot during a 10-year period.
  3. Large herbivores were able to decelerate diversity declines and compositional change in the species-rich old-growth forest, but only decelerated compositional change in the secondary forest. In contrast, declines in species richness and abundance were unaffected by large herbivores on either forest.
  4. The buffering effects of large herbivores were strongly nonlinear and contingent on the initial level of diversity at the patch scale: highly diverse communities suffered the strongest collapse in the absence of large herbivores. Thus, larger buffering effects of large herbivores on the old-growth forest are the logical consequence of large herbivores buffering the many high diversity plant communities found in this forest. Conversely, as the secondary forest held fewer high diversity patches, buffering effects on the secondary forest were weak.
  5. Synthesis and applications. Our study indicates that large herbivores have moderate yet critical effects on slowing down community change and diversity loss of highly diverse plant communities, thus suggesting that the conservation of (and potentially trophic rewilding with) large herbivores is a fundamental nature-based solution for averting the global collapse of the strongholds of biodiversity. Its buffering effects on biodiversity loss operate at very small spatial scales, are likely contingent on successional stage and are most effective in old-growth or high diversity secondary forests.
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United Kingdom Sully Offline
Ecology & Rewilding
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#53

Interesting paper which has been used to argue that there isn't actually an unnaturally high population of deer in the UK, due to the biomass-productivity relationship. Flawed however as there is a marked ecological difference in the spatial organisation between grazers and browsers. Still, worth thinking about, and true that any amount of deer without predation will supress woody growth. and it wasn't a deer overpopulation which originally felled all the trees. 

Exploring a natural baseline for large-herbivore biomass in ecological restoration

Abstract


  1. Large herbivores provide key ecosystem processes, but have experienced massive historical losses and are under intense pressure, leaving current ecosystems with dramatically simplified faunas relative to the long-term evolutionary norm. Hampered by a shifting baseline, natural levels of large-herbivore biomass are poorly understood and seldom targeted. This ‘Decade of ecosystem restoration’ calls for evidence-based targets for restoring the natural diversity and biomass of large herbivores.
  2. We apply the scaling of the consumer–producer relationship to a global dataset of large-herbivore density in natural areas. The analyses reveal that African ecosystems generally have much higher large-herbivore biomass and also the strongest consumer–producer relationship. For Europe, Asia and South America, there are no significant relationships with primary productivity indicative of impoverished faunas. Compared to expectations from the African scaling relation, large-herbivore biomass in ecosystems outside Africa is considerably lower than expected.
  3. Synthesis and applications. Ecological restoration and rewilding entail restoration of a natural grazing process. Our findings indicate that many nature reserves are depleted in large-herbivore biomass, judged from their primary productivity. Meanwhile, overexploitation by seasonal livestock grazing takes place in other areas. It is thus difficult, but urgent, to reach scientific consensus regarding a natural baseline for large-herbivore biomass. Until such agreement has been reached, we recommend to manage, or rewild, large herbivores in year-round near-natural grazing and without predefined density targets, but following natural and fluctuating resource availability with minimal management intervention. The establishment of experimental rewilding sites with reactive herbivore management is needed to further advance our understanding of natural grazing density.
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United Kingdom Sully Offline
Ecology & Rewilding
*****
#54

Landscapes shaped from the top down: predicting cascading predator effects on spatial biogeochemistry

Abstract

Spatial heterogeneity in ecological systems can result from animal-driven top–down processes, but despite some theoretical attention, the emergence of spatial heterogeneity from feedbacks caused by animals is not well understood empirically. Interactions between predators and prey influence animal movement and associated nutrient transport and release, generating spatial heterogeneity that cascades throughout ecological systems. Here, we synthesize the existing literature to evaluate the mechanisms by which terrestrial predators can generate spatial heterogeneity in biogeochemical processes through consumptive and non-consumptive effects. Overall, we propose that predators increase heterogeneity in ecosystems whenever predation is intense and spatially variable, whereas predator–prey interactions homogenize ecosystems whenever predation is weak or diffuse in space. This leads to several testable hypotheses: 1) that predation and carcass deposition at high-predation risk sites stimulate positive feedbacks between predation risk and nutrient availability; 2) that prey generate nutrient hotspots when they concentrate activity in safe habitats, but instead generate nutrient subsidies when they migrate daily between safe and risky habitats; 3) that herbivore body size mediates risk effects, such that megaherbivores are more likely to homogenize ecosystems and predator loss in general will tend to homogenize ecosystems. Testing these hypotheses will advance our understanding of whether predators amplify landscape heterogeneity in ecological systems.
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United Kingdom Sully Offline
Ecology & Rewilding
*****
#55

Experimental evidence that effects of megaherbivores on mesoherbivore space use are influenced by species' traits

Abstract

  1. The extinction of 80% of megaherbivore (>1,000 kg) species towards the end of the Pleistocene altered vegetation structure, fire dynamics and nutrient cycling world-wide. Ecologists have proposed (re)introducing megaherbivores or their ecological analogues to restore lost ecosystem functions and reinforce extant but declining megaherbivore populations. However, the effects of megaherbivores on smaller herbivores are poorly understood.
  2. We used long-term exclusion experiments and multispecies hierarchical models fitted to dung counts to test (a) the effect of megaherbivores (elephant and giraffe) on the occurrence (dung presence) and use intensity (dung pile density) of mesoherbivores (2–1,000 kg), and (b) the extent to which the responses of each mesoherbivore species was predictable based on their traits (diet and shoulder height) and phylogenetic relatedness.
  3. Megaherbivores increased the predicted occurrence and use intensity of zebras but reduced the occurrence and use intensity of several other mesoherbivore species. The negative effect of megaherbivores on mesoherbivore occurrence was stronger for shorter species, regardless of diet or relatedness.
  4. Megaherbivores substantially reduced the expected total use intensity (i.e. cumulative dung density of all species) of mesoherbivores, but only minimally reduced the expected species richness (i.e. cumulative predicted occurrence probabilities of all species) of mesoherbivores (by <1 species).
  5. Simulated extirpation of megaherbivores altered use intensity by mesoherbivores, which should be considered during (re)introductions of megaherbivores or their ecological proxies. Species' traits (in this case shoulder height) may be more reliable predictors of mesoherbivores' responses to megaherbivores than phylogenetic relatedness, and may be useful for predicting responses of data-limited species.
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United Kingdom Sully Offline
Ecology & Rewilding
*****
#56

Species distribution models rarely predict the biology of real populations

Abstract

Species distribution models (SDMs) are widely used in ecology. In theory, SDMs capture (at least part of) species' ecological niches and can be used to make inferences about the distribution of suitable habitat for species of interest. Because habitat suitability is expected to influence population demography, SDMs have been used to estimate a variety of population parameters, from occurrence to genetic diversity. However, a critical look at the ability of SDMs to predict independent data across different aspects of population biology is lacking. Here, we systematically reviewed the literature, retrieving 201 studies that tested predictions from SDMs against independent assessments of occurrence, abundance, population performance, and genetic diversity. Although there is some support for the ability of SDMs to predict occurrence (~53% of studies depending on how support was assessed), the predictive performance of these models declines progressively from occurrence to abundance, to population mean fitness, to genetic diversity. At the same time, we observed higher success among studies that evaluated performance for single versus multiple species, pointing to a possible publication bias. Thus, the limited accuracy of SDMs reported here may reflect the best-case scenario. We discuss the limitations of these models and provide specific recommendations for their use for different applications going forward. However, we emphasize that predictions from SDMs, especially when used to inform conservation decisions, should be treated as hypotheses to be tested with independent data rather than as stand-ins for the population parameters we seek to know.
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United Kingdom Sully Offline
Ecology & Rewilding
*****
#57

No pervasive relationship between species size and local abundance trends


Abstract

Although there is some evidence that larger species could be more prone to population declines, the potential role of size traits in determining changes in community composition has been underexplored in global-scale analyses. Here, we combine a large cross-taxon assemblage time series database (BioTIME) with multiple trait databases to show that there is no clear correlation within communities between size traits and changes in abundance over time, suggesting that there is no consistent tendency for larger species to be doing proportionally better or worse than smaller species at local scales.
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United Kingdom Sully Offline
Ecology & Rewilding
*****
#58

As expected

"Small body size, fossorial behaviour and herbivorous diets were associated with the highest population densities, whereas large size, aerial behaviour and carnivorous diets were related to the lowest densities."

Population density estimates for terrestrial mammal species
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