Ungulate migrations are assumed to stem from learning and cultural transmission of information regarding seasonal distribution of forage, but this hypothesis has not been tested empirically. We ...compared the migratory propensities of bighorn sheep and moose translocated into novel habitats with those of historical populations that had persisted for hundreds of years. Whereas individuals from historical populations were largely migratory, translocated individuals initially were not. After multiple decades, however, translocated populations gained knowledge about surfing green waves of forage (tracking plant phenology) and increased their propensity to migrate. Our findings indicate that learning and cultural transmission are the primary mechanisms by which ungulate migrations evolve. Loss of migration will therefore expunge generations of knowledge about the locations of high-quality forage and likely suppress population abundance.
Studies on trophic cascades involving large carnivores typically are limited by a lack of replication and control, giving rise to a spirited debate over the ecological role of these iconic species. ...We argue that much of this debate can be resolved by decomposing the trophic cascade hypothesis into three constituent interactions, quantifying each interaction individually, and accommodating alternative hypotheses. We advocate for a novel approach that couples the rigor characterizing foundational work on trophic cascades (i.e., from studies carried out in mesocosm and whole lake systems) with the conservation relevance of large carnivore-dominated food webs. Because of their iconic status, it is crucial that inferences about the ecological role of large carnivores rise to meet the same rigorous standards to which other studies in community ecology are held.
Large carnivores are believed to play a key role in determining ecosystem properties via trophic cascades. While the recovery of large carnivore populations is generally heralded as a conservation success story, the common assertion that such recoveries alter plant communities and other ecosystem properties is currently not supported by the standards of evidence expected in other scientific disciplines.
There have been very few replicated and controlled experiments documenting evidence for trophic cascades involving large carnivores, leaving a knowledge gap with crucial implications for ecology and wildlife conservation.
The absence of a mechanistic understanding of food web dynamics and weak inference in many studies combine to obfuscate the mechanisms underlying if and how large carnivores affect ecosystems.
Human-wildlife conflicts restrict conservation efforts, especially for wide-ranging animals whose home ranges overlap with human activities. We conducted a study to understand conflicts with, and ...factors influencing the perceived value of an expanding population of onagers (Equus hemionus onager) in local communities in southern Iran. We asked about locals' perceptions of six potential management strategies intended to lessen human-onager conflict. We found that human-onager conflict was restricted to 45% of respondents within the Bahram-e-Goor Protected Area, all of whom were involved in farming or herding activities. Locals within the protected area were more knowledgeable about onagers and valued onagers more than those living outside the protected area. The perceived value of onagers increased with level of education, total annual income, and perceptions of onager population trends; the perceived value of onagers decreased with the magnitude of conflict between onagers and locals. To tolerate or avoid conflicts with onagers, locals were supportive of monetary compensation and changing from a traditional lifestyle to industrialized farming (for farmers) or livestock production (for herders) with the help of government; locals did not support selling land to the government. Our study is among the first in human-wildlife conflict and local attitudes towards an endangered species and its recovery in Iran. We conclude that current levels of human-onager conflict are relatively low and perceived value of onagers is still relatively high. Therefore, wildlife authorities should consider the development of mitigation strategies with local communities before conflicts intensify.
The search for predictions of species diversity across environmental gradients has challenged ecologists for decades. The humped-back model (HBM) suggests that plant diversity peaks at intermediate ...productivity; at low productivity few species can tolerate the environmental stresses, and at high productivity a few highly competitive species dominate. Over time the HBM has become increasingly controversial, and recent studies claim to have refuted it. Here, by using data from coordinated surveys conducted throughout grasslands worldwide and comprising a wide range of site productivities, we provide evidence in support of the HBM pattern at both global and regional extents. The relationships described here provide a foundation for further research into the local, landscape, and historical factors that maintain biodiversity.
Understanding how predation risk and plant defenses interactively shape plant distributions is a core challenge in ecology. By combining global positioning system telemetry of an abundant antelope ...(impala) and its main predators (leopards and wild dogs) with a series of manipulative field experiments, we showed that herbivores’ risk-avoidance behavior and plants’ antiherbivore defenses interact to determine tree distributions in an African savanna.Well-defended thorny Acacia trees (A. etbaica) were abundant in low-risk areas where impala aggregated but rare in high-risk areas that impala avoided. In contrast, poorly defended trees (A. brevispica) were more abundant in high- than in low-risk areas. Our results suggest that plants can persist in landscapes characterized by intense herbivory, either by defending themselves or by thriving in risky areas where carnivores hunt.
The forage maturation hypothesis (FMH) states that energy intake for ungulates is maximised when forage biomass is at intermediate levels. Nevertheless, metabolic allometry and different digestive ...systems suggest that resource selection should vary across ungulate species. By combining GPS relocations with remotely sensed data on forage characteristics and surface water, we quantified the effect of body size and digestive system in determining movements of 30 populations of hindgut fermenters (equids) and ruminants across biomes. Selection for intermediate forage biomass was negatively related to body size, regardless of digestive system. Selection for proximity to surface water was stronger for equids relative to ruminants, regardless of body size. To be more generalisable, we suggest that the FMH explicitly incorporate contingencies in body size and digestive system, with small‐bodied ruminants selecting more strongly for potential energy intake, and hindgut fermenters selecting more strongly for surface water.
The forage maturation hypothesis (FMH) states that energy intake for ungulates is maximised when forage biomass is at intermediate levels. To be more generalisable, we suggest that the FMH state that energy intake for ungulates is maximised at different phenological stages, depending on body size and digestive system.
Evolutionary modification has produced a spectrum of animal defence traits to escape predation, including the ability to autotomize body parts to elude capture. After autotomy, the missing part is ...either replaced through regeneration (for example, in urodeles, lizards, arthropods and crustaceans) or permanently lost (such as in mammals). Although most autotomy involves the loss of appendages (legs, chelipeds, antennae or tails, for example), skin autotomy can occur in certain taxa of scincid and gekkonid lizards. Here we report the first demonstration of skin autotomy in Mammalia (African spiny mice, Acomys). Mechanical testing showed a propensity for skin to tear under very low tension and the absence of a fracture plane. After skin loss, rapid wound contraction was followed by hair follicle regeneration in dorsal skin wounds. Notably, we found that regenerative capacity in Acomys was extended to ear holes, where the mice exhibited complete regeneration of hair follicles, sebaceous glands, dermis and cartilage. Salamanders capable of limb regeneration form a blastema (a mass of lineage-restricted progenitor cells) after limb loss, and our findings suggest that ear tissue regeneration in Acomys may proceed through the assembly of a similar structure. This study underscores the importance of investigating regenerative phenomena outside of conventional model organisms, and suggests that mammals may retain a higher capacity for regeneration than was previously believed. As re-emergent interest in regenerative medicine seeks to isolate molecular pathways controlling tissue regeneration in mammals, Acomys may prove useful in identifying mechanisms to promote regeneration in lieu of fibrosis and scarring.
Good neighbors make good defenses Coverdale, Tyler C.; Goheen, Jacob R.; Palmer, Todd M. ...
Ecology (Durham),
August 2018, Volume:
99, Issue:
8
Journal Article
Peer reviewed
Intraspecific variation in plant defense phenotype is common and has wide-ranging ecological consequences. Yet prevailing theories of plant defense allocation, which primarily account for ...interspecific differences in defense phenotype, often fail to predict intraspecific patterns. Furthermore, although individual variation in defense phenotype is often attributed to ecological interactions, few general mechanisms have been proposed to explain the ubiquity of variable defense phenotype within species. Here, we show experimentally that associational refuges and induced resistance interact to create predictable intraspecific variation in defense phenotype in African savanna plants. Physically defended species from four families (Acanthaceae, Asparagaceae, Cactaceae, and Solanaceae) growing in close association with spinescent Acacia trees had 39–78% fewer spines and thorns than did isolated conspecifics. For a subset of these species, we used a series of manipulative experiments to show that this variability is maintained primarily by a reduction in induced responses among individuals that seldom experience mammalian herbivory, whether due to association with Acacia trees or to experimental herbivore exclusion. Unassociated plants incurred 4- to 16-fold more browsing damage than did associated individuals and increased spine density by 16–38% within one month following simulated browsing. In contrast, experimental clipping induced no net change in spine density among plants growing beneath Acacia canopies or inside long-term herbivore exclosures. Associated and unassociated individuals produced similar numbers of flowers and seeds, but seedling recruitment and survival were vastly greater in refuge habitats, suggesting a net fitness benefit of association. We conclude that plant-plant associations consistently decrease defense investment in this system by reducing both the frequency of herbivory and the intensity of induced responses, and that inducible responses enable plants to capitalize on such associations in heterogeneous environments. Given the prevalence of associational and induced defenses in plant communities worldwide, our results suggest a potentially general mechanism by which biotic interactions might predictably shape intraspecific variation in plant defense phenotype.
Understanding cooperation is a central challenge in biology, because natural selection should favor "free-loaders" that reap benefits without reciprocating. For interspecific cooperation (mutualism), ...most approaches to this paradox focus on costs and benefits of individual partners and the strategies mutualists use to associate with beneficial partners. However, natural selection acts on lifetime fitness, and most mutualists, particularly longer-lived species interacting with shorter-lived partners (e.g., corals and zooxanthellae, tropical trees and mycorrhizae) interact with multiple partner species throughout ontogeny. Determining how multiple partnerships might interactively affect lifetime fitness is a crucial unexplored link in understanding the evolution and maintenance of cooperation. The tropical tree Acacia drepanolobium associates with four symbiotic ant species whose short-term individual effects range from mutualistic to parasitic. Using a long-term dataset, we show that tree fitness is enhanced by partnering sequentially with sets of different ant symbionts over the ontogeny of a tree. These sets include a "sterilization parasite" that prevents reproduction and another that reduces tree survivorship. Trees associating with partner sets that include these "parasites" enhance lifetime fitness by trading off survivorship and fecundity at different life stages. Our results demonstrate the importance of evaluating mutualism within a community context and suggest that lifespan inequalities among mutualists may help cooperation persist in the face of exploitation.
Despite the shared prediction that the width of a population's dietary niche expands as food becomes limiting, the Niche Variation Hypothesis (NVH) and Optimal Foraging Theory (OFT) offer contrasting ...views about how individuals alter diet selection when food is limited.
Classical OFT predicts that dietary preferences do not change as food becomes limiting, so individuals expand their diets as they compensate for a lack of preferred foods. In contrast, the NVH predicts that among‐individual variation in cognition, physiology or morphology create functional trade‐offs in foraging efficiency, thereby causing individuals to specialize on different subsets of food as food becomes limiting.
To evaluate (a) the predictions of the NVH and OFT and (b) evidence for physiological and cognitive‐based functional trade‐offs, we used DNA microsatellites and metabarcoding to quantify the diet, microbiome and genetic relatedness (a proxy for social learning) of 218 moose Alces alces across six populations that varied in their degree of food limitation.
Consistent with both the NVH and OFT, dietary niche breadth increased with food limitation. Increased diet breadth of individuals—rather than increased diet specialization—was strongly correlated with both food limitation and dietary niche breadth of populations, indicating that moose foraged in accordance with OFT. Diets were not constrained by inheritance of the microbiome or inheritance of diet selection, offering support for the little‐tested hypothesis that functional trade‐offs in food use (or lack thereof) determine whether populations adhere to the predictions of the NVH or OFT.
Our results indicate that both the absence of strong functional trade‐offs and the digestive physiology of ruminants provide contexts under which populations should forage in accordance with OFT rather than the NVH. Also, because dietary niche width increased with increased food limitation, OFT and the NVH provide theoretical support for the notion that plant–herbivore interaction networks are plastic rather than static, which has important implications for understanding interspecific niche partitioning. Lastly, because population‐level dietary niche breadth and calf recruitment are correlated, and because calf recruitment can be a proxy for food limitation, our work demonstrates how diet data can be employed to understand a populations' proximity to carrying capacity.
The Niche Variation Hypothesis and Optimal Foraging Theory offer contrasting views about how individuals alter diet selection when food is limited. In accordance with Optimal Foraging Theory, the niche breadth of moose increased with increased food limitation because of increased individual niche breadth rather than increased individual specialization.
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