Influence Population Size Research Articles

Large-scale fence modifications increase nest survival in sage-grouse

Livestock grazing is the most common land-use practice in aridland ecosystems of the American West. Widespread and long-term declines of greater sage-grouse (Centrocercus urophasianus), an umbrella species for other sagebrush-associated vertebrates, has challenged land managers to find solutions to help bolster populations. Livestock grazing infrastructure (e.g., fences) among western rangelands are one potential factor impacting sage-grouse populations as nest survival – a key demographic rate that influences population size – can be 4x higher when placed >100 m away from the nearest fence. We implemented the first-ever long-term (8 years) and large-scale (70 km in length) management action designed to evaluate changes in nest survival related to fence modifications in the Centennial Valley of Montana, USA. Fence modifications included perch deterrents placed atop fence posts to reduce perching by avian nest predators. Additionally, the bottom fence wire was raised to 45 cm from the ground to reduce the funneling of mammalian predators along fences who are in search of carcasses from collisions and/or nests placed near fences. Using a Bayesian statistical framework, we found that fence modifications increased 28-day nest survival within 100 m of mitigated fences by an average of 10.6 % (85 % CRI: 3.7–24.9 %). The difference in survival between fence types was most pronounced for modified fences in low elevations, while modified fences resulted in higher survival rates throughout the nesting season. Our findings suggest that modifying fences designed to reduce the search efficiency of sage-grouse nest predators appear to benefit nest survival in sage-grouse. The highlighted fence modification technique offers practitioners a tool to advance grazing systems that reduce the impacts of grazing infrastructure on greater sage-grouse.

Rising above the noise: the influence of population dynamics on the evolution of acoustic signaling

Acoustic signaling is employed by many sexually reproducing species to select for mates and enhance fitness. However, signaling in dense populations can create an auditory background, or chorus, which may interfere with a signal receiver’s phonotactic selectivity, or the ability to distinguish individual signals. Feedback between the strength of an individual’s signal, phonotactic selectivity, and population size, may interact in complex ways to impact the evolution of signaling within a population, potentially leading to the emergence of silence. Here we formulate a general model that captures the dynamic feedback between individual acoustic signalers, phonotactic selectivity, and the population-level chorus to explore the eco-evolutionary dynamics of an acoustic trait within a population. We find that population dynamics have a significant influence on the evolutionary dynamics of the signaling trait, and that very sharp transitions separate conspicuous from silent populations. Our framework also reveals that increased phonotactic selectivity promotes the stability of signaling populations, and that transitions from signaling to silence are prone to hysteresis. We suggest that understanding the relationship between factors influencing population size, such as environmental productivity, as well as factors influencing phonotactic selectivity, such as anthropogenic noise, are central to understanding the complex mosaic of acoustically signaling and silent populations.

The possible impact of escaped captive American mink (Neogale vison) on the population of feral mink in Denmark.

The Danish feral mink (Neogale vison) population can be divided into wild-born and captive-born mink newly escaped from a farm. The impact of the captive-born mink on the population of feral population is unknown. Captive-born mink has lately been estimated to make up 25-30% of the feral mink population. In December 2020 Danish mink farms were decommissioned until January 2023. The aim of this study was to: 1) Examine whether a supplementation of farmed mink into the feral mink population influence the population growth and extinction rate of the feral mink, 2) Investigate which parameters affect the viability in feral mink populations the most. The age and mortality of 351 mink and the reproduction of 85 adult females culled by hunters from 2019-2022 were determined in three distinct geographic areas of Denmark (Jutland, Zealand, and Bornholm). VORTEX simulations were used to model the population viability and to simulate the impact of a supplementation of captive-born mink into the wild population. Simulations show that changes by 30% in the parameters: fecundity, percentages of breeding females and mortality influenced population size influenced the final population size significantly. The initial population size and inbreeding did not affect the population growth significantly. The simulations showed that the mink population in the regions of Jutland and Zealand could go extinct within 15 to 30 years without any supplementation of captive-born mink to the feral population. The population on Bornholm will however remain stable with current levels of mortality and reproduction even without supplementation of captive mink.

Effects of different diets on thermal tolerance in the silkworm, Bombyx mori

AbstractThe survival of species is negatively impacted by the increased frequency and intensity of high‐temperature episodes caused by increased global warming. Thermal tolerance can influence population size and the geographic distribution of species, which translates into species‐wide responses to climate and affects interactions between communities of species. The silkworm, Bombyx mori (L.) (Lepidoptera: Bombycidae), is an ectotherm and an internationally recognized model insect for studying sensitivity to the environment. In the present study, we investigated the effects of different diets on the thermal tolerance of silkworm. As such, it was identified that silkworms reared on an artificial diet in instars I–III and mulberry leaves in instar IV (referred as the AM group) exhibited faster weight gain and higher antioxidant enzyme activity at 35 °C, whereas silkworms reared only on mulberry leaves (referred as the ML group) exhibited upregulated transcript levels of key genes regulating antioxidant enzyme signaling pathways including Akt, CncC, and keap1, significantly increased reactive oxygen species (ROS) levels, and severely impaired midgut activity at 35 °C. Thus, the AM group presented stronger thermal tolerance. These findings suggest that diet can affect the thermal tolerance of silkworm. This research improved our understanding of the molecular, biochemical, and physiological changes caused by thermal stress and laid the groundwork for future research regarding the mechanism underlying thermal tolerance. Furthermore, this study provides an important reference for the conservation of biodiversity in the context of global warming.

Movement drives population dynamics of one of the most mobile ungulates on Earth: Insights from a mechanistic model.

Long-distance movements are hypothesized to positively influence population size and stability of mobile species. We tested this hypothesis with a novel modeling approach in which moving herbivores interact with the environment created by a dynamic global vegetation model using highly mobile Mongolian gazelles in the eastern Mongolian grasslands as a case study. Gazelle population dynamics were modeled from 1901 to 2018 under two scenarios, one allowing free movement and one restricting movement. Gazelles were 2.2 times more abundant when they could move freely and were extirpated in 71% of the study area when mobility was restricted. Mobility resulted in greater population increases during times of abundant forage and smaller population decreases during drought. Reduced thermoregulatory costs associated with climate change, combined with an increase in vegetation biomass, increased gazelle abundance. Since high abundances often resulted in overgrazing and, thus, extirpation when movement was restricted, mobility had an important role in maintaining higher densities. The novel modeling approach shows how accounting for not just herbivore but also plant ecophysiology can improve our understanding of the population dynamics of highly mobile herbivores, in particular when examining the effects of habitat and climate change. Since the model simulates herbivores based on general physiological mechanisms that apply across large herbivores and the vegetation model can be applied globally, it is possible to adapt the model to other large-herbivore systems.

A comparison of foraging‐range sizes, flight distances and foraging habitat preferences in urban and rural House Sparrow (Passer domesticus) populations

Lack of food for nestlings is a crucial factor influencing population size and dynamics in birds. It is one of the most cited reasons for recent House Sparrow Passer domesticus population declines in cities and rural settlements. However, a detailed comparative study of habitat use by parents delivering food to offspring in different environments is still missing. To obtain the most detailed information on fine‐scale foraging habitat selection, foraging‐range size, flight distance and foraging duration in typical Central European urban and rural environments, we conducted systematic observations of colour‐ringed focal individuals feeding their offspring. We found that urban House Sparrows had larger foraging‐range sizes and longer foraging distances than rural birds. Additionally, some preferred habitats, such as ruderal and woody vegetation, occurred less frequently in the urban area and consequently increased flight distance to key sources of invertebrate prey. In both environments, the most selected habitats – bin storage areas and poultry holdings – offered a stable and rich but probably lower quality ‘fast food’ source. Birds were willing to fly a longer distance to forage at bin storage areas, tall ruderal vegetation and poultry holdings. Our findings imply that natural food sources in the urban environment are scarce and scattered. Due to the improvement of socio‐economic status associated with better handling of waste products in both urban and rural environments, sprawl of highly urbanized areas and intensification of farming, important foraging habitats have thus decreased. We highlight the importance of maintaining suitable small‐ and medium‐scale farms in rural areas and suggest improvements in the management of green spaces in all types of human settlements that may support House Sparrow populations.

Warmer water increases early body growth of northern pike (Esox lucius), but mortality has larger impact on decreasing body sizes

Large fish species often display truncated size distributions related to harvest. In addition, temperature, food availability and density dependence affect body growth and together with natural mortality influence population size structure. Here we study changes in body growth, size distributions and mortality in both harvested and nonharvested populations of northern pike (Esox lucius) over 50 years along the Baltic Sea coast and in Lake Mälaren, Sweden. For coastal pike, body growth has increased coincidentally with increasing water temperatures, yet in the last two decades there has been a decrease of larger individuals. In Lake Mälaren, in contrast, size distributions and body growth were stationary despite similar increases in water temperature. A dominance of slow-growing individuals in older age classes was evident in all studied populations, also in the no-take zone, suggesting other factors than fishing contribute to the mortality pattern. We propose that increasing temperatures have favoured body growth in coastal areas, but this has been counteracted by increased mortality, causing pike sizes to decline. To regain larger coastal pike, managers need to consider multiple measures that reduce mortality.

A Three-Pronged Approach to Studying Sublethal Insecticide Doses: Characterising Mosquito Fitness, Mosquito Biting Behaviour, and Human/Environmental Health Risks.

Simple SummaryExtensive research has been carried out to assess the effects of sublethal pyrethroid doses on mosquito fitness and behaviour. Although pyrethroids are mainly used as insecticides, they can also act as repellents, depending on the dosage and/or exposure time. Females and males of two laboratory-reared mosquito species (Culex pipiens and Aedes albopictus) were exposed to five treatments in the laboratory: three doses of the pyrethroid prallethrin, as well as an untreated and a negative control. Effects on mosquito fitness, mosquito biting behaviour, and human and environmental health were evaluated. Sublethal prallethrin doses were found to decrease mosquito population size, longevity, and biting rate while posing low risks to human and environmental health. Such changes in adult mosquito fitness and behaviour could reduce the ability of mosquitoes to transmit diseases and, consequently, help limit public health risks. Although these promising results suggest sublethal insecticide doses could offer a new approach to controlling species that transmit diseases, more work is needed to identify the proper balance among regulatory requirements, contexts of usage, and human and environmental health benefits.Worldwide, pyrethroids are one of the most widely used insecticide classes. In addition to serving as personal protection products, they are also a key line of defence in integrated vector management programmes. Many studies have assessed the effects of sublethal pyrethroid doses on mosquito fitness and behaviour. However, much remains unknown about the biological, physiological, demographic, and behavioural effects on individual mosquitoes or mosquito populations when exposure occurs via spatial treatments. Here, females and males of two laboratory-reared mosquito species, Culex pipiens and Aedes albopictus, were exposed to five different treatments: three doses of the pyrethroid prallethrin, as well as an untreated and a negative control. The effects of each treatment on mosquito species, sex, adult mortality, fertility, F1 population size, and biting behaviour were also evaluated. To compare knockdown and mortality among treatments, Mantel–Cox log-rank tests were used. The results showed that sublethal doses reduced mosquito survival, influencing population size in the next generation. They also provided 100% protection to human hosts and presented relatively low risks to human and environmental health. These findings emphasise the need for additional studies that assess the benefits of using sublethal doses as part of mosquito management strategies.

Intensity of grass invasion negatively correlated with population density and age structure of an endangered dune plant across its range

Invasive species are a global threat to ecosystem biodiversity and function; non-native grass invasion has been particularly problematic in sparsely vegetated ecosystems such as open dunes. Native plant population responses to invasion, however, are infrequently translated to landscape scales, limiting the effectiveness of these data for addressing conservation issues. We quantified population density, total population size, and age class distribution of the federally-endangered plant species Antioch Dunes evening primrose (Oenothera deltoides subsp. howellii), at sites along a non-native grass invasion gradient in California, USA. We then scaled relationships between invasion and plant density across the species’ range using spatial models and remote sensing data. Adult and juvenile O. deltoides subsp. howellii densities were more than 10 times higher in non-invaded areas (grids with 10% total plant cover) when compared to highly-invaded areas (grids with 80% total plant cover). The ratio of O. deltoides subsp. howellii juveniles to adults decreased to less than 1 at 54% total cover, highlighting sensitivity of the regeneration niche to invasion. Spatial models mapped hotspots of O. deltoides subsp. howellii abundance and population structure across the landscape at sub-meter scales. Scaling the impacts of increasing invasion on plant species of conservation concern holds promise when coupled with remote sensing approaches, especially in naturally low-cover ecosystems where readily available metrics (e.g., Normalized Difference Vegetation Index) can be used to quantify invasion. These spatial models inform how future invasive species management may influence population size and spatial distribution of species of conservation concern.

Isolation promotes abundance and species richness of fishes recruiting to coral reef patches

Habitat area and fragmentation are recognised as important factors that influence population size, community structure and extinction risk. Abundance and species richness universally increase with habitat area. However, the effects of different aspects of habitat fragmentation, including variation in patch size, number and isolation are often not distinguished from each other or the overall effects of habitat amount. Here we experimentally tested predictions concerning the effects of isolation on abundance, species richness and community structure of coral reef fishes colonising patch reefs by constructing clusters of patches of the same number and size, but manipulating reef spacing. Hexagonal clusters of 7 experimental patch reefs (6 edge and 1 central) with 3 levels of isolation (1 m, 5 m, and 15 m spacing) were established at Kavieng, Papua New Guinea and colonisation was recorded after 6 weeks in 2014. We also deployed video cameras to test whether isolation affected the activity of transient predatory fishes. As predicted, isolation had a positive effect on both mean abundance and species richness at both the cluster and patch scale. The cumulative abundance and species richness exhibited linear increases in relation to habitat area within clusters (from 1 to 7 patch reefs), but the slope increased with the degree of isolation. There was some evidence that transient predators remained longer and were more successful when patches were close together, which may explain the lower abundance and richness of juvenile fish assemblages on more aggregated patch reefs. This study demonstrates that while habitat amount is fundamentally important, isolation has significant effects that will need to be distinguished from other aspects of fragmentation when examining the processes structuring reef fish communities.

Implications of Sea Level Rise for Bee Communities in Rural Eastern Virginia Coastal Habitats

In the coastal mid-Atlantic region of the USA, landscapes are a mosaic of upland habitats (woodland, grassland, old fields and farmland) and low-lying coastal salt marsh. Flooding and salinization of coastal areas due to sea-level rise result in the conversion of upland habitats to salt marsh, and change the relative proportion of habitat types surrounding coastal farmland. This has the potential to influence population sizes of organisms living in this area and could alter the ecosystem services, such as pollination, that these habitats provide. To examine the potential outcome of these habitat conversions, we used blue vane traps at 14 sites along the Eastern Shore of Virginia (USA) to compare the bee communities of salt marsh, old fields and agricultural fields. Although there was no difference among habitat types for total bee abundance per site, we found that the coastal marsh is depauperate in bee species relative to old fields and agricultural fields, and that the bee species using the marsh habitat tend to be specialists of plant families that are common in the marsh (Asteraceae and Malvaceae) but are relatively uncommon in local agriculture. Thus, the transition of upland areas to marsh not only has the potential to impact agricultural productivity directly through salt water intrusion, ultimately it may also reduce the species richness of native bees available to provide pollination services to coastal agriculture.

From individuals to populations: How intraspecific competition shapes thermal reaction norms

Abstract Most ectotherms follow the temperature‐size rule (TSR): in cold environments individuals grow slowly but reach a large asymptotic length. Intraspecific competition can induce plastic changes of growth rate and asymptotic length and competition may itself be modulated by temperature. Our aim was to disentangle the joint effects of temperature and intraspecific competition on growth rate and asymptotic length. We used two distinct clonal lineages of the Collembola Folsomia candida, to describe thermal reaction norms of growth rate, asymptotic length and reproduction over six temperatures between 6 and 29°C. In parallel, we measured the long‐term size structure and dynamics of springtail populations reared under the same temperatures to measure growth rates and asymptotic lengths in populations and to quantify the joint effects of competition and temperature on these traits. We show that intraspecific competition modulates the temperature‐size rule. In dense populations there is a direct negative effect of temperature on asymptotic length, but there is no temperature dependence of the growth rate, the dominant factor regulating growth being competition. The two lineages responded differently to the joint effects of temperature and competition on growth and asymptotic size and these genetic differences have marked effects on population structure along our temperature gradient. Our results reinforce the idea that the TSR of ectotherms can be modulated by biotic and abiotic stressors when studied in non‐optimal laboratory experiments. Untangling complex interactions between the environment and demography will help to understand how growth trajectories respond to environmental change and how climate change may influence population size structure. A free Plain Language Summary can be found within the Supporting Information of this article.

Influence of cisco (Coregonus artedi, Lesueur) on muskellunge (Esox masquinongy, Mitchill) mean length, population size structure, and maximum size in northern Wisconsin lakes

Population size structure and maximum size of managed sportfish populations are dictated by abiotic, biotic, ecosystem, and anthropogenic influences. In their native ranges of northern Wisconsin, muskellunge (Esox masquinongy) and cisco (Coregonus artedi) are co-adapted cool- and cold-water species where cisco presence may influence population size structure and maximum size of muskellunge. We tested whether muskellunge size structure indices (length-frequency distributions, proportional size distribution), mean length, and mean maximum length of muskellunge differed when cisco were present or absent in Ceded Territory of Wisconsin (CTWI) lakes during 2015–2018. Cisco presence had a positive influence on size structure and mean length of individual muskellunge within populations. In contrast, cisco presence had no influence on the mean maximum length of muskellunge observed in CTWI populations suggesting that other factors may be better predictors of this metric than cisco presence. In cisco lakes, mean muskellunge length was negatively correlated with mean cisco length suggesting that gape limitation may be a factor influencing population size structure and individual growth rates. Therefore, cisco populations with primarily large individuals may be unavailable to muskellunge as forage. Our results suggest that cisco are an important forage species for some aspects of muskellunge population ecology; however, other factors may also contribute to muskellunge population size structure and maximum size outcomes. As such, conservation of remaining cisco populations in Wisconsin is critical because they influence muskellunge population ecology in lakes where the species coexist. Future research is needed to better understand the interactions of cisco, abiotic and biotic factors, and anthropogenic influences on muskellunge growth dynamics.

Effects of grazing intensity, habitat area and connectivity on snail-shell nesting bees

The effects of habitat loss and fragmentation on wild bee populations are still not fully understood. Availability of resources, parasitism and habitat connectivity might influence population sizes of bees. Whereas floral resources for wild bees have been considered in research and conservation, nesting resources have been largely neglected as these are challenging to investigate. Snail shells are the exclusive nesting cavities for several Osmia species and provide a good - but so far unused - tool to study factors driving bee population dynamics. We investigated the effects of habitat area, connectivity and management of semi-natural grasslands on populations of snail-shell nesting bees. On 23 calcareous grasslands, we monitored snail shell colonization by providing empty snail shells as nesting resources, and recorded flower-visitor interactions.Five snail-shell nesting Osmia species were found on the grasslands, which made almost a quarter of recorded bee flower visits. Three species colonized the offered snail shells with high variation between study sites, Osmia species, and snail shell size. Habitat area had a positive effect on the population size of the habitat specialist Osmia aurulenta, whereas the more generalist species Osmia bicolor was positively influenced by habitat connectivity. Destruction rates of snail shells increased with sheep grazing intensity, leading to an estimated loss of more than a third of all bee nests. We conclude that large and connected habitats benefit bee populations in fragmented landscapes, while conservation management regimes should take into account potential negative effects of grazing on specific nesting resources of specialized bee species.

The implications of rapid eco‐evolutionary processes for biological control ‐ a review

AbstractNovel environmental conditions experienced by introduced species can drive rapid evolution of diverse traits. In turn, rapid evolution, both adaptive and non‐adaptive, can influence population size, growth rate, and other important ecological characteristics of populations. In addition, spatial evolutionary processes that arise from a combination of assortative mating between highly dispersive individuals at the expanding edge of populations and altered reproductive rates of those individuals can accelerate expansion speed. Growing experimental evidence shows that the effects of rapid evolution on ecological dynamics can be quite large, and thus it can affect establishment, persistence, and the distribution of populations. We review the experimental and theoretical literature on such eco‐evolutionary feedbacks and evaluate the implications of these processes for biological control. Experiments show that evolving populations can establish at higher rates and grow larger than non‐evolving populations. However, non‐adaptive processes, such as genetic drift and inbreeding depression can also lead to reduced fitness and declines in population size. Spatial evolutionary processes can increase spread rates and change the fitness of individuals at the expansion front. These examples demonstrate the power of eco‐evolutionary dynamics and indicate that evolution is likely more important in biocontrol programs than previously realized. We discuss how this knowledge can be used to enhance efficacy of biological control.

Jinggangmycin-Induced UDP-Glycosyltransferase 1-2-Like Is a Positive Modulator of Fecundity and Population Growth in Nilaparvata lugens (Stål) (Hemiptera: Delphacidae).

The antibiotic jinggangmycin (JGM) is broadly applied in Chinese rice producing regions to control rice blight, a fungal disease. Aside from protecting rice plants from the disease, JGM leads to the unexpected action of stimulating brown planthopper (BPH; Nilaparvata lugens; Hemiptera: Delphacidae) reproduction to the extent it can influence population sizes. The JGM-induced BPH population growth has potential for severe agricultural problems and we are working to understand and mitigate the mechanisms of the enhanced reproduction. UDP-glucuronosyltransferases (UGTs) are multifunctional detoxification enzymes responsible for biotransformation of diverse lipophilic compounds. The biological significance of this enzyme family in insect fecundity is not fully understood, however, upregulated UGT12 in JGM-treated BPH, may influence fecundity through metabolism of developmental hormones. This idea prompted our hypothesis that NlUGT12 is a positive modulator of BPH reproductive biology. JGM treatment led to significant increases in accumulations of mRNA encoding NlUGT12, numbers of eggs laid, oviposition period, juvenile hormone III titers, and fat body, and ovarian protein contents. dsUGT12 treatment suppressed NlUGT12 expression and reversed JGM-enhanced effects, resulting in under-developed ovaries and reduced expression of juvenile hormone acid methyltransferase and the JH receptor, methoprene tolerant. Application of the JH analog, methoprene, on dsUGT12 treated-females partially reversed the dsUTG12 influence on vitellogenin synthesis and on NlUGT12 expression. These results represent an important support for our hypothesis.

Water Availability Coincides with Population Declines for an Endangered Butterfly

As global climate change causes population declines across numerous taxa, it becomes critical to understand the specific pathway by which climatic and anthropogenic factors influence population size. Water availability is a key environmental condition that links climate and humans to species response, especially for rare or threatened butterflies that are highly sensitive to changes in climate and the surrounding landscape. We use the wetland-dependent endangered St. Francis’ satyr butterfly (Neonympha mitchellii francisci) to test how changes in water availability affect population size via changes in host plant growth. We show that long-term declines in water availability are directly linked to a decline in host plant growth and contributed to a population decrease of 95% for St. Francis’ satyrs in the past decade, threatening the persistence of the species. Recent restoration work, which includes efforts to increase water availability via hardwood removal, has been successful in increasing population numbers. Many butterflies are broadly dependent on water availability and flow, and only by understanding the specific pathway that directly links water availability to species response can we make effective conservation plans to prepare for the altered water conditions of the future.

The importance of core habitat for a threatened species in changing landscapes

Abstract Habitat loss, fragmentation, and alteration of the landscape matrix are interdependent processes, collectively responsible for most recent species extinctions. Thus, determining the extent to which these landscape processes affect animals is critical for conservation. However, researchers have often assumed that interdependent effects are independently related to animals’ responses, underestimating the importance of one or several landscape processes in driving species declines. We demonstrate how to disentangle the interdependent effects of habitat amount, fragmentation, and edge context on population size by assessing abundance of a rapidly declining grassland songbird species (grasshopper sparrow Ammodramus savannarum) in eastern Kansas (USA). We conducted >7,000 point count surveys at >2,000 sites over two breeding seasons, then modelled the direct, interactive, and indirect effects of landscape factors on abundance within spatial scales (200‐, 400‐, 800‐, and 1,600‐m radii) relevant to our focal species’ dispersal behaviour. Sparrow abundance correlated most strongly with landscape structure within 400‐m radii, increasing nonlinearly with grassland area and decreasing with the proportion of grassland near cropland or woody edges. Sparrows’ negative response to cropland edges was mostly an added, indirect consequence of reduced grassland area, whereas sparrows’ stronger negative response to woody edges was not attributable to variation in grassland area. Fragmentation and edge context mattered most in landscapes comprising c. 50%–80% grassland. Synthesis and applications. In our research, abundance of a threatened grassland songbird was influenced more by core grassland area (a function of total grassland area, fragmentation, and edge context) than total grassland area per se. Moreover, a local extinction threshold of c. 50% grassland indicated that small amounts of habitat were unsuitable for our focal species regardless of habitat configuration or matrix type. Local extinction thresholds in response to habitat area provide clear baseline targets for land managers; above those thresholds, configuration and the matrix can be modified to increase abundance of edge‐sensitive animals. Conflicting evidence in the literature regarding the importance of fragmentation and matrix features could be partially explained by species‐level traits, or methodological issues such as defining landscapes at ecologically arbitrary spatial scales, assessing landscape quality using species richness, and ignoring interactive and indirect effects.

Male contributions during mating increase female survival in the disease vector mosquito Aedes aegypti

Aedes aegypti is a vector of medically important viruses including those causing Zika, dengue, and chikungunya. During mating, males transfer a number of proteins and other molecules to the female and these components of the male ejaculate are essential in shifting female post-mating behaviors in a number of insect species. Because these molecules are highly variable by species, and female post-mating behavior by species is also varied, behavioral assays testing the function of the ejaculate are necessary before we can develop control strategies targeting the mating system to reduce mosquito populations. Because increased survival in mosquitoes strongly increases vectorial capacity and can influence population sizes and potential risk we tested the effect of mating on female survival. The ejaculate can either promote or reduce female survival, as both have been shown in multiple insect species, yet this effect has not been directly assessed in mosquitoes. We compared survival of females in four treatment groups: mated females, virgin females, and virgin females injected with either an extract from the male reproductive glands or a saline control. Survival, blood feeding frequency, fecundity and cumulative net reproductive rate (R0) were determined after multiple feedings from a human host. Our results confirm that male reproductive gland substances increase female fecundity and blood feeding frequency, resulting in dramatic increases in fitness (R0). We also demonstrate, for the first time, an effect of male reproductive gland extracts alone on female survival, regardless of whether or not the female ingested a vertebrate blood meal. Thus, the effects of MAG extract on survival are not secondary effects from altered blood feeding. Collectively, we demonstrate a direct role for Ae. aegypti male-derived molecules on increasing female fitness, reproductive success and, ultimately, transmission potential for vector borne pathogens.

Biotic interactions enhance survival and fitness in the caddisfly Micropterna sequax (Trichoptera: Limnephilidae)

Patches of coarse particulate organic matter in lowland streams are inhabited by many different macroinvertebrate species, yet knowledge of interactions among the members of these assemblages is scarce. In a mesocosm experiment we aimed to determine the effect of interspecific interactions on species survival and fitness of two caddisfly species. It was hypothesized that, as a result of positive interactions, mixed species populations would yield higher survival and fitness than single species populations. Larvae of two caddisfly species, Micropterna sequax and Potamophylax rotundipennis, were reared in single species and mixed species populations. Emergence rate was recorded and adult fitness was measured in terms of wingspan and biomass. We found that in mixed populations, emergence rate, wing length and biomass of M. sequax were higher than in single species populations. P. rotundipennis was only significantly, yet negatively, affected in terms of biomass of the male individuals. This study showed that occurring together with other species holds advantages for M. sequax, and emphasizes the importance of species diversity in streams. Furthermore, the observed positive effects on survival and fecundity might influence population sizes of the interacting species, in turn affecting macroinvertebrate-mediated ecosystem processes such as leaf litter decomposition.