Abstract Insect population dynamics are the result of an interplay between intraspecific competition, trophic interactions and external forces such as weather conditions, but studying how these processes combine to determine population change is challenging. We investigate mechanisms of population dynamics in a natural, low density insect population. Eggs and larvae of the noctuid moth, Abrostola asclepiadis, develop on its host plant during summer. The population density, and mortality, was closely monitored throughout this period during 15 years. Densities fluctuated between one and two orders of magnitude. Egg -- larval developmental time varied substantially among years, with lower survival in cool summers with slower development. This was presumably due to the prolonged exposure to a large guild of polyphagous arthropod enemies. We also found a density dependent component during this period, that could be a result of intraspecific competition for food among old larvae. Dynamics during the long period from pupation in late summer through winter survival in the ground to adult emergence and oviposition the next year displayed few clear patterns and more unexplained variability, thus giving a more random appearance. The population hence shows more unexplained or unpredictable variation during the long wintering period, but seems more predictable over the summer egg-larval period. Our study illustrates how weather - via a window of exposure to enemies and in combination with density-dependent processes - can determine the course of population change through the insect life cycle.
We measured the content of nitrogen and phosphorus, as well as nitrogen stable isotopes in plant biomass and marmot faeces in a distance gradient up to 20 meters from marmot burrows in an extremely arid glacier valley in Eastern Pamir, Tajikistan. The goal of this study was to test well-known mechanisms of ecosystem engineering by burrowing animals in previously unstudied conditions. We captured aerial images of the area inhabited by marmots to study the spatial distribution of vegetation. There was no relationship between the presence of burrows and vegetation cover. Burrow mounds were not colonised by plants, as opposed to other ecosystems, where mounds are often microhabitats that enhance plant diversity. A significant increase in N and P in aboveground green plant biomass in the proximity of burrows was found in one out of six studied species. Stable N isotopes did not give further insight into N routing, contrary to our expectations. We assume that plant growth is strongly limited by water availability, which prevents them from utilizing the local increase in nutrients, certainly provided by marmot activity. The results are contrary to numerous studies which showed that the role of burrowing animals as ecosystem engineers increases with increasing abiotic stress, including aridity. This shows a lack of this type of study in the end of the gradient of abiotic factors.
1 Understanding the effect of ground types on foraging movements of ground-dwelling arthropods is a key step to managing their spatial distribution as required for successful conservation biological control. Indeed, fine movements at the centimetre scale can strongly influence the foraging ability of pest predators. However, because RFID or harmonic tracking techniques are not yet suitable for small species and video tracking focuses on uniform and light backgrounds, foraging movements have rarely been studied in relation to ground types. 2 We present a method to track a ground-dwelling arthropod (the earwig Euborellia caraibea) at night, walking on two contrasted ground types : bare soil and soil partly covered with a stratum of banana plant residues allowing individuals to hide periodically. 3 The tracking of individuals within these ground types was achieved by infrared light, tagging individuals, video treatments and semi-automatic cleaning of trajectories. We tested different procedures to obtain segments with identical durations to quantify speeds and sinuosities. These procedures were characterised by the junction time gap between trajectory fragments, the rediscretisation time of trajectories, and whether or not to use interpolation to fill in missing points in the trajectories. 4 Earwigs exhibited significantly slower and more sinuous movements on soil with banana plant residues than on bare soil. Long time gaps for trajectory junction, extended rediscretisation times and interpolation were complementary means to integrate concealed movements in the trajectories. The highest slowdown in plant residues was detected when the procedure could account for longer periods under the residues. 5 These results suggest that earwigs spent a significant amount of time concealed by the residues. Additionally, the residues strongly decreased the earwigs’ movement. Since the technical solutions presented in this study are inexpensive, easy to set up and replicate, they represent valuable contributions to the emerging field of video monitoring.
1. This study is the first to quantitatively measure of the courtship flights of Latham’s snipe (Gallinago hardwickii), a migratory shorebird on the East Asian-Australasian Flyway, which is nearly threatened in their major breeding ground in Japan. 2. We localised the fine-scale movements of their display flights performed at high altitude and high speed, using a 16-channel microphone array, and assessed the direction from which each sound arrived using robot audition. 3. Preliminary analyses of the azimuthal and elevation angles of the display flights partially revealed a fine-scale flight trajectory, in which a male Latham’s snipe gradually gained elevation while vocalising sharp and harsh repeating calls until it reached the flight peak elevation and then dove down to the ground with a winnowing along wetland zones without tall vegetation. 4. Not only is this observation methodologically useful for better understanding Latham’s snipe display flight site selection, but can also be extended to investigate other rare nocturnal or crepuscular birds, that are too timid to risk ringing or tagging.
1. The recovery of terrestrial carnivores in Europe is a conservation success story. Initiatives focused on restoring top predators, require information on how resident species may interact with the re-introduced species as their interactions have the potential to alter food webs, yet such data are scarce for Europe. 2. In this study, we assessed patterns of occupancy and interactions between three carnivore species in the Romanian Carpathians. Romania houses one of the few intact carnivore guilds in Europe, making it an ideal system to assess intraguild interactions, and serve as a guide for reintroductions elsewhere. 3. We used camera trap data from two seasons in Transylvanian forests to assess occupancy and co-occurrence of carnivores using multispecies occupancy models. 4. Mean occupancy in the study area was highest for lynx ( winter= 0.76 95% CI: 0.42-0.92; autumn= 0.71 CI: 0.38-0.84) and wolf (winter= 0.60 CI: 0.34-0.78; autumn= 0.81 CI: 0.25-0.95) and lowest for wildcat (winter= 0.40 CI: 0.19-0.63; autumn= 0.52 CI: 0.17-0.78) 5. We found that marginal occupancy predictors for carnivores varied between seasons. We also found differences in predictors of co-occupancy between seasons for both lynx-wolf and wildcat-wolf co-occupancy. For both seasons, we found that conditional occupancy probabilities of all three species were higher when another species was present. 6. Our results indicate that while there are seasonal differences in predictors of occupancy and co-occupancy of the three species, co-occurrence in our study area is high, and is dependent on the existence of continuous, relatively undisturbed forests. 7. Terrestrial carnivore recovery efforts are ongoing worldwide. Insights into interspecific relations between carnivore species are critical when considering the depauperate communities they are introduced in. Our work showcases that apex carnivore coexistence is possible, but dependent on protection afforded to forest habitats and their prey base.
Explaining food web dynamics, stability, and functioning depend substantially on understanding of feeding relations within a community. Bulk stable isotope ratios (SIRs) in natural abundance are well-established tools to express direct and indirect feeding relations as continuous variables across time and space. Along with bulk SIRs, the SIRs of individual amino acids (AAs) are now emerging as a promising and complementary method to characterize the flow and transformation of resources across a diversity of organisms, from microbial domains to macroscopic consumers. This significant AA-SIR capacity is based on empirical evidence that a consumer’s SIR, specific to an individual AA, reflects its diet SIR coupled with a certain degree of isotopic differences between the consumer and its diet. However, many empirical ecologists are still unfamiliar with the scope of applicability and the interpretative power of AA-SIR. To fill these knowledge gaps, we here describe a comprehensive approach to both carbon and nitrogen AA-SIR assessment focusing on two key topics: pattern in AA-isotope composition across spatial and temporal scales, and a certain variability of AA-specific isotope differences between the diet and the consumer. On this basis we review the versatile applicability of AA-SIR to improve our understanding of physiological processes as well as food web functioning, allowing us to reconstruct dominant basal dietary sources and trace their trophic transfers at the specimen and community levels. Given the insightful and opportunities of AA-SIR, we suggest future applications for the dual use of carbon and nitrogen AA-SIR to study more realistic food web structures and robust consumer niches, which are often very difficult to explain in nature.
1. Evergreen dwarf shrubs respond swiftly to warming in the cool and dry High Arctic, but their response in the warmer Low Arctic, where they are expected to be outcompeted by taller species under future warming, remains to be clarified. 2. Here, 12,528 annual growth increments, covering 122 years (1893-2014), were measured of 764 branches from 25 individuals of the evergreen dwarf shrub Cassiope tetragona from a Low-Arctic erect dwarf-shrub tundra site in western Greenland. In addition, branch initiation and mortality frequency time-series were developed. The influence of seasonal climate and correspondence with fluctuations in regional normalized difference vegetation index (NDVI), a satellite-proxy for vegetation productivity, were studied. 3. Winter temperatures were an important co-driver, summer temperatures the main driver of growth. During past and recent warm episodes, shrub growth diverged from summer temperatures. In recent decades, early summer precipitation has become the main growth-limiting factor for some individuals, likely through micro-topography-determined soil moisture availability, and more than half of the shrubs studied became irresponsive to summer temperatures. There was correspondence between climatic drivers, C. tetragona growth and branch initiation frequency, and satellite-observed vegetation productivity, suggesting the area’s shrub-dominated tundra vegetation is limited by similar climatic factors. Winter warming events were likely the predominant cause of branch mortality, while branching increased after years with poor growth and cooler-than-average summers. 4. Synthesis These findings show that the erect dwarf-shrub tundra in the Low Arctic has and will likely become less temperature- and increasingly moisture-limited and that winter warming supports shrub growth, but increased extreme winter warming event-frequency may increase branch mortality and vegetation damage. Such counter-acting mechanisms could offer an explanation for the vegetation stability observed over large parts of the Arctic.
Research on among individual variation in behavior has increased rapidly in recent years. It is intuitively appealing that among individual variation in behavior has ecological consequences and among the most likely to be affected is trophic niche. Bold individuals, with the tendency to be explorative and risk tolerant, can be less likely to alter their foraging behavior across contexts and therefore forage more consistently. Stable isotopes are a useful tool to retrospectively estimate ecological niche and have been found to correlate to foraging behavior in the wild. It is now pressing to extent studies to further examine the ecological or evolutionary relevance of personality. We examined if common behavioral traits were correlated to ecological niche in the wild using a rapid behavioral assay and δ13C and δ15N stable isotopes from fin and muscle reflecting ecological niche for the previous weeks and months. We found that latency to explore, as a proxy for boldness, correlated to values of δ13C with bolder fish having lower δ13C values. Moreover, latency to explore also explained variation in the change in individual stable isotope niche over time. These results highlight the long-term ecological importance of among individual variation in behavior and are among the first to support a correlation of laboratory measures of behavior and ecological niche in the wild.
Heterogeneity in riverine habitats acts as a template for species evolution that influences river communities at different spatio-temporal scales. Although birds are conspicuous elements of these communities, the roles of phylogeny, functional traits and habitat character in their niche-use or species’ assembly have seldom been investigated. We explored these themes by surveying multiple headwaters over 3000 m of elevation in the Himalayan Mountains of India where specialist river birds reach their greatest diversity on Earth. After ordinating community composition, species traits and habitat character, we investigated whether river-bird traits varied with elevation in ways that were constrained or independent of phylogeny, hypothesising that trait patterns reflect environmental filtering. Community composition and trait representation varied strongly with elevation and river naturalness as species that foraged in the river/riparian ecotone gave way to small insectivores with obligate links to the river channel. These trends were influenced strongly by phylogeny as communities became more clustered by functional traits at higher elevation. Phylogenetic signals varied among traits, however, and were reflected in body mass, bill size and tarsus length more than in body size, tail length and breeding strategy. These variations imply that community assembly in high altitude river birds reflects a blend of phylogenetic constraint and habitat filtering coupled with some proximate niche-based moulding of trait character. We suggest that the regional co-existence of river birds in the Himalaya is facilitated by the same array of factors that together reflect the highly heterogeneous template of river habitats provided by these mountain headwaters.
Human activities can degrade the quality of coral reefs, cause a decline in fish species richness and functional diversity and an erosion of the ecosystem services provided. Environmental DNA metabarcoding (eDNA) has been proposed as an alternative to Underwater Visual Census (UVC) to offer more rapid assessment of marine biodiversity to meet management demands for ecosystem health indices. Taxonomic information derived from sequenced eDNA can be combined with functional traits and phylogenetic positions to generate a variety of ecological indices describing ecosystem functioning. Here, we inventoried reef fish assemblages of two contrasted coastal areas of Curaçao, (i) in close proximity to the island’s capital city and (ii) in a more remote area under more limited anthropogenic pressure. We sampled eDNA by filtering large volumes of sea water (2 x 30L) along 2km boat transects, which we coupled with species ecological properties related to habitat use, trophic level and body size to investigate the difference in fish taxonomic composition, functional and phylogenetic indices recovered from eDNA metabarcoding between these two distinct coastal areas. Despite no marked difference in species richness, we found a higher phylogenetic diversity in proximity to the city, but a higher functional diversity on the more isolated reef. Composition differences between coastal areas were associated with different frequencies of reef fish families. Because of a partial reference database, eDNA only partly matched those detected with UVC, but eDNA surveys nevertheless provided rapid and robust species occupancy responses to contrasted environments. eDNA metabarcoding coupled with functional and phylogenetic diversity assessment can serve the management of coastal habitats under increasing threat from global changes.
High-throughput DNA sequencing technologies make it possible now to sequence entire genomes relatively easily. Complete genomic information obtained by whole genome resequencing (WGS) can aid in identifying and delineating species even if they are extremely young, cryptic or morphologically difficult to discern and closely related. Yet for taxonomic or conservation biology purposes WGS can remain cost-prohibitive, too time-consuming, and often constitute a “data overkill”. Rapid and reliable identification of species (and populations) that is also cost-effective is possible based on species-specific markers that can be discovered by WGS. Based on WGS data we designed a PCR restriction fragment length polymorphism (PCR-RFLP) assay for 19 Neotropical Midas cichlid populations (Amphilophus cf. citrinellus), that includes all 13 described species of this species complex. Our work illustrates that identification of species and populations (i.e., fish from different lakes) can be greatly improved by designing genetic markers using available “high resolution” genomic information. Yet, our work also shows that even in the best-case scenario, when whole-genome resequencing information is available, unequivocal assignments remain challenging when species or populations diverged very recently, or gene flow persists. In summary, we provide a comprehensive workflow on how to design RFPL markers based on genome re-sequencing data, how to test and evaluate their reliability, and discuss the benefits and pitfalls of our approach.
Crustaceans comprise an ecologically and morphologically diverse taxonomic group. They are typically considered resilient to many environmental perturbations found in marine and coastal environments, due to effective physiological regulation of ions and hemolymph pH, and a robust exoskeleton. Ocean acidification can affect the ability of marine calcifying organisms to build and maintain mineralized tissue and poses a threat for all marine calcifying taxa. Currently, there is no consensus on how ocean acidification will alter the ecologically-relevant exoskeletal properties of crustaceans. Here, we present a systematic review and meta-analysis on the effects of ocean acidification on the crustacean exoskeleton, assessing both exoskeletal ion content (calcium and magnesium) and functional properties (biomechanical resistance and cuticle thickness). Our results suggest that the effect of ocean acidification on crustacean exoskeletal properties varies based upon seawater pCO2 and species identity, with significant levels of heterogeneity for all analyses. Calcium and magnesium content were significantly lower in animals held at pCO2 levels of 1500-1999 μatm as compared to those under ambient pCO2. At lower pCO2 levels, however, statistically significant relationships between changes in calcium and magnesium content within the same experiment were observed: a negative relationship between calcium and magnesium content at pCO2 of 500-999 μatm and a positive relationship at 1000-1499 μatm. Exoskeleton biomechanics, such as resistance to deformation (microhardness) and shell strength, also significantly decreased under pCO2 regimes of 500-999 μatm and 1500-1999 μatm, indicating functional exoskeletal change coincident with decreases in calcification. Overall, these results suggest that the crustacean exoskeleton can be susceptible to ocean acidification at the biomechanical level, potentially predicated on changes in ion content, when exposed to high influxes of CO2. Future studies will need to accommodate the high variability of crustacean responses to ocean acidification, as well as ecologically-relevant ranges of pCO2 conditions, when designing experiments with conservation-level endpoints.
1. Prairie dogs (Cynomys sp.) are considered keystone species and ecosystem engineers for their grazing and burrowing activities (summarized here as disturbances). As climate changes and its variability increases, the mechanisms underlying organisms’ interactions with their habitat will likely shift. Understanding the mediating role of prairie dog disturbance on vegetation structure, and its interaction with environmental conditions through time, will increase knowledge on the risks and vulnerability of grasslands. 2. Here, we compared how plant taxonomic and functional diversity metrics, along with community-weighted trait means (CWM), respond to prairie dog disturbance across grassland types and seasons in a conservation priority, semiarid grassland of Northeast Mexico. 3. Our findings suggest that functional metrics and CWM analyses responded to interactions between prairie dog disturbance, grassland type and season, whilst species diversity and cover measures were less sensitive to the role of prairie dog disturbance. Contrary to previous studies, we found weak evidence that prairie dog disturbance has a negative effect on vegetation structure, except for minimal effects on C4 and graminoid cover, which depend mainly on season. Grassland type and season explained most of the effects on plant functional and taxonomic diversity as well as CWM traits. Furthermore, we found that leaf area as well as forb and annual cover increased during the wet season, independent of prairie dog disturbance. 4. Our results provide evidence that prairie dog disturbance is less important than grassland type and that environmental effects have a stronger role than grazing and animal disturbances on vegetation. We argue that a focus on disturbance and grazing effects is misleading, and instead attention is needed on the relationships between vegetation and environmental conditions which will be critical to understand semi-arid grassland dynamics in the region. In addition, explicit management strategies to mitigate climate change would need to consider these relationships
Conservation of wide-ranging species is a challenge owing to their movement in an increasingly fragmented world. Long-distance dispersal has significant implications for ecosystem functioning, and such movement becomes challenging while navigating through a heterogeneous and human-dominated landscape. Here, we describe one of the longest dispersal journey by a sub-adult male tiger through GPS telemetry in Central India. We analyzed movement metrics, directionality, and space use during three behavioural stages of dispersal. We also used the clustering method to identify resting and kill sites (n = 89). T1-C1 dispersed a straight-line distance of 315 km over 225 days, moving an average 8.4 km/day and covering a cumulative displacement of ̵̴ 3000 km. Movement during post-dispersal was higher (mean = 465.6 m/h) than those during dispersal (mean = 376.6 m/h) and pre-dispersal (mean = 132.2 m/h), respectively. Moreover, movement during the night was significantly faster than during the day in all three phases. Likewise, during dispersal, the movement was faster (mean = 518.2 m/h) and more directional (knight = 0.19) at night than day. The average size of clusters was 1.68 ha and primarily away from human habitation (mean = 1875.6 m). The mean cluster duration (46.31 hr) was higher in the non-forested area but was smaller in size than inside the forest (p< 0.05). The individual crossed roads faster (mean= 1880.9 m/hr) than it travelled during other times. During the post-dispersal phase, T1-C1 established its home range with an area of 319.48 sq. km. (95% dBBMM). The dispersal event highlights the long-distance and multiscale movement behaviour in a heterogeneous landscape. Moreover, small forest patches play a key role in maintaining large carnivore connectivity while dispersing through a human-dominated landscape. Our study underlines how documenting the long-distance movement and integrating it with modern technology can improve conservation management decisions.
1. Global climate change affects many aspects of biology and has been shown to cause body size changes in animals. However, suitable datasets allowing the analysis of long-term relationships between body size and climate are rare. 2. The size of the skull, often used as a proxy for body size, does not change much in fully grown vertebrates, but some soricine shrews shrink their skull and brain in winter and regrow it in spring. This is thought to be a winter adaptation in these high-metabolic, nonhibernating animals, as a smaller brain size reduces energy requirements. 3. Climate could thus affect not only the overall size but also the pattern of the size change, i.e., Dehnel’s Phenomenon, in these shrews. 4. We assessed the impact of the changes in climate on the overall skull size and the different stages of Dehnel’s phenomenon in skulls of the common shrew, Sorex araneus, collected over 50 years in the Białowieża Forest, NE Poland. 5. Overall skull size decreased, along with increasingly mild winters and decreasing soil moisture, which determined the availability of the shrews’ main food source, earthworms. The magnitude of Dehnel’s phenomenon increased over time, indicating an increasing selection pressure on animals in winter. Overall, climate clearly affected the common shrew’s overall size as well as its seasonal size changes. With the current acceleration in climate change, the effects on the distribution range of this cold-adapted species may be quite severe.
In heterogeneous landscapes, habitat preference constitutes a crucial link between landscape and population-level processes such as density and sex ratios. We conducted a non-invasive genetic study of white-tailed deer in southern Finland using fecal samples. We estimated deer density as a function of landcover type using a Spatial Capture-Recapture (SCR) model. Second-order habitat selection of white-tailed deer revealed particularly high densities in fields and mixed forest, and third-order selection was related to distance to fields and transitional woodlands (clearcuts). Including landscape heterogeneity improved model fit compared with assuming a homogenous landscape. Our findings underline the importance of including habitat covariates when estimating density.
The nocturnal activities of predators and prey are influenced by several factors, including physiological adaptations, habitat quality and, we suspect, corresponds to changes in brightness of moonlight according to moon phase. In this study, we used a dataset from 102 camera traps to explore which factors are related with the activity pattern of North China leopards (Panthera pardus japonensis) in Shanxi Tieqiaoshan Provincial Nature Reserve (TPNR), China. We found that nocturnal activities of leopards were irregular during four different lunar phases, and while not strictly lunar philic or lunar phobic, their temporal activity was highest during the brighter moon phases (especially the last quarter) and lower during the new moon phase. On the contrary, roe deer (Capreolus pygargus) exhibited lunar philic activity, while wild boar (Sus scrofa) and Tolai hare (Lepus tolai) were evidently lunar phobic, with high and low temporal activity during the full moon, respectively. In terms of temporal overlap, that there was positive overlap between leopards and their prey species, including roe deer (Capreolus pygargus) and Tolai hare (Lepus tolai), while leopard activity did not dip to the same low level of wild boar during the full moon phase. Generally, our results suggested that besides moonlight risk index (MRI), cloud cover and season have diverse effects on leopard and prey nocturnal activity. Finally, distinct daytime and nighttime habitats were identified, with leopards, wild boar and Tolai hare all using lower elevations at night and higher elevations during the day, while leopards and roe deer were closer to secondary roads during the day than at night.
The neurotransmitter dopamine has been shown to play an important role in modulating behavioural, morphological and life-history responses to food abundance. However, costs of expressing high dopamine levels remain poorly studied and are essential for understanding the evolution of the dopamine system. Negative maternal effects on offspring size from enhanced maternal dopamine levels have previously been documented in Daphnia. Here, we tested whether this translates into fitness costs in terms of lower starvation resistance in offspring. We exposed Daphnia magna mothers to aqueous dopamine (2.3 mg/L or 0 mg/L for the control) at two food levels (ad libitum versus 30% ad libitum) and recorded a range of maternal life history traits. The longevity of their offspring was then quantified in the absence of food. In both control and dopamine treatments, mothers that experienced restricted food ration had lower somatic growth rates and higher age at maturation. Maternal food restriction also resulted in production of larger offspring that had a superior starvation resistance, compared to ad libitum groups. However, although dopamine exposed mothers produced smaller offspring than controls at restricted food ration, these smaller offspring survived longer under starvation. Hence, maternal dopamine exposure provided an improved offspring starvation resistance. We discuss the relative importance of proximate and ultimate causes for why D. magna may not evolve towards higher endogenous dopamine levels despite the fitness benefits this appears to have.