Changes In Insect Communities Research Articles

Light and Malaise traps tell different stories about the spatial variations in arthropod biomass and method‐specific insect abundance

Abstract Conclusions reached in meta‐analyses of changes in insect communities may be influenced by method‐specific sampling biases, which may lead to inappropriate conservation measures. We argue that the contradictory conclusions regarding terrestrial insect biomass, abundance and richness patterns are, at least partly, due to methodological limitations that reflect taxon‐specific responses to environmental changes. In this study, light and Malaise traps were simultaneously deployed to sample insects at 52 plots in a temperate forest in Germany along gradients of elevation (>1000 m) and canopy openness (3%–100%). These gradients were used as predictors in models of total arthropod biomass according to the two trapping methods and in models of abundance and richness of three commonly targeted groups: nocturnal moths, sampled using light traps, and hoverflies and bees, collected with Malaise traps. A comparison of the total arthropod biomass obtained with the two methods revealed contrary results along the canopy openness gradient. Biomass in light traps showed a decreasing trend with increasing canopy openness while biomass in Malaise traps increased. The same opposing pattern was found for the abundance of selected taxa. The different patterns describing spatial variation of arthropod communities obtained using light and Malaise traps can be explained by differences in the taxa predominantly collected. Regarding the ongoing debate on insect decline, our results demonstrate that comparing different taxa from different taxon‐specific traps is inappropriate. Thus, we recommend that future meta‐analyses take into account the sampling methods and taxon‐specific responses to environmental changes.

Late Holocene anthropogenic landscape change in northwestern Europe impacted insect biodiversity as much as climate change did after the last Ice Age.

Since the last Ice Age (ca 115 000–11 700 years ago), the geographical ranges of most plants and animals have shifted, expanded or contracted. Understanding the timing, geographical patterns and drivers of past changes in insect communities is essential for evaluating the biodiversity implications of future climate changes, yet our knowledge of long-term patterns is limited. We applied a network modelling approach to the recent fossil record of northwestern European beetles to investigate how their taxonomic and trait composition changed during the past 16 000 years. We found two major changes in beetle faunas 4000–3500 and 10 000–9500 years ago, coinciding with periods of human population growth in the Late Holocene and climate warming in the Early Holocene. Our results demonstrate that humans have affected insect biodiversity since at least the introduction of agropastoralism, with landscape-scale effects that can be observed at sites away from areas of direct human impact.

Climate-induced forest dieback drives compositional changes in insect communities that are more pronounced for rare species

Species richness, abundance and biomass of insects have recently undergone marked declines in Europe. We metabarcoded 211 Malaise-trap samples to investigate whether drought-induced forest dieback and subsequent salvage logging had an impact on ca. 3000 species of flying insects in silver fir Pyrenean forests. While forest dieback had no measurable impact on species richness, there were significant changes in community composition that were consistent with those observed during natural forest succession. Importantly, most observed changes were driven by rare species. Variation was explained primarily by canopy openness at the local scale, and the tree-related microhabitat diversity and deadwood amount at landscape scales. The levels of salvage logging in our study did not explain compositional changes. We conclude that forest dieback drives changes in species assemblages that mimic natural forest succession, and markedly increases the risk of catastrophic loss of rare species through homogenization of environmental conditions.

Human-Mediated Land Use Change Drives Intraspecific Plant Trait Variation.

In the Anthropocene, more than three quarters of ice-free land has experienced some form of human-driven habitat modification, with agriculture dominating 40% of the Earth’s surface. This land use change alters the quality, availability, and configuration of habitat resources, affecting the community composition of plants and insects, as well as their interactions with each other. Landscapes dominated by agriculture are known to support a lower abundance and diversity of pollinators and frequently larger populations of key herbivore pests. In turn, insect communities subsidized by agriculture may spill into remaining natural habitats with consequences for wild plants persisting in (semi) natural habitats. Adaptive responses by wild plants may allow them to persist in highly modified landscapes; yet how landscape-mediated variation in insect communities affects wild plant traits related to reproduction and defense remains largely unknown. We synthesize the evidence for plant trait changes across land use gradients and propose potential mechanisms by which landscape-mediated changes in insect communities may be driving these trait changes. Further, we present results from a common garden experiment on three wild Brassica species demonstrating variation in both defensive and reproductive traits along an agricultural land use gradient. Our framework illustrates the potential for plant adaptation under land use change and predicts how defense and reproduction trait expression may shift in low diversity landscapes. We highlight areas of future research into plant population and community effects of land use change.

A deep convolutional neural network based classifier for passive acoustic monitoring of neotropical katydids

Insects occupy a central position in terrestrial trophic webs, consuming large amounts of vegetation and being consumed by other fauna. Changes in insect communities can have widespread effects across an ecosystem. In addition, having relatively small dispersal distances and stereotyped calls, insects make for an excellent choice as a monitoring target. Here, passive acoustic monitoring is employed for studying katydids, a relative of crickets and grasshoppers that are often charismatic mimics of leaves and sticks. In a prior study, call repertoires of over 60 species of katydids were established using individuals captured on Barro Colorado Island, Panama. These recordings are used in training a deep convolutional neural network based classifier, for subsequent analyses of long-term field recordings that are currently being collected. Coarse imbalances in the number of captured individuals per species and in their calling rates resulted in an unbalanced dataset. Furthermore, differences in recording equipment and in the recording practices posed challenges to achieving a well-rounded dataset. The measures taken to address these impediments will be discussed along with the classifier design choices. The classifier yielded >98% mean-average-precision over 60 classes on an exclusive validation split. Results of its application on field recordings will be presented.

Responses of bark beetle (Coleoptera: Curculionidae: Scolytinae) community structure to green-tree retention in pine tree forest from Korea

This study was aimed to investigate the response of bark beetle community structure to green-tree retention in a Korean pine tree forest between 2013 and 2015. Five types of retention methods were evaluated to investigate the retention effect on insect community structure at various sites in Keunjeogol, Samcheok, and Gangwon-do. Lindgren funnel traps were installed to collect insects from July to August, over a 3-year period. Overall, 690 individuals and 29 species of Scolytinae were collected, with populations of insects appearing to gradually increase by each year of the study. Results of the insect community analysis showed that most survey sites presented a higher diversity than the control site annually except in 2015. This study can be used as a baseline dataset for the long-term study of early changes in insect community in response to green-tree retention in forests.

Long‐term changes in ground beetle (Coleoptera: Carabidae) assemblages in Scotland

1. One‐way, directional changes in both plant and animal associations are likely to be occurring as a result of changing climate. Current knowledge of long‐term cycles in insect communities is scarce, and therefore it is difficult to assess whether the observed changes in insect communities are the first part of a long‐term trend or parts of normal cycles.2. In this study multivariate methods were used to describe the trends in ground beetle (Coleoptera: Carabidae) assemblages over an 18‐year (1994–2011) period at two Scottish sites. In order to have a deeper insight into the underlying processes, both environmental factors and the species driving the detected changes were investigated.3. In four out of the six sample transects, insect community compositions showed trends rather than fluctuating patterns. Hierarchical cluster analysis also revealed a clear separation, after accounting for sampling location and broad habitat, between early and later years of sampling. Decreasing annual maximum temperatures and increasing precipitation were identified as the main environmental drivers. Although increased rainfall was expected to be beneficial for hygrophilous species, in the transects in this study generalist species increased in dominance.4. The increasing importance of generalists, in the communities studied here, underlines the vulnerability of the specialist species and urges greater effort in their conservation. Assemblage changes along different trajectories at the sites in the present study could only be tracked using multivariate methods; commonly used diversity indices proved to be unsatisfactory. Therefore, the exclusive use of simple diversity indices should be discouraged and multivariate methods should be preferred in environmental assessments and conservation planning.

Restoration of Subalpine Species-Rich Grasslands: Short-TermvsLong-Term Changes in the Density and Diversity of above-Ground Insects

Due to decrease in the area of extensively managed, semi-natural grasslands, that contribute to high biodiversity level preservation, the conversion of highly productive meadows to extensively managed, species-rich grasslands is now regarded as an important task for nature conservation. The aim of this long-term study was to assess the significance of restoration measures for diversity and trophic structure of above-ground insect community. That study challenges some weaknesses of previous studies as it was conducted with the use of suction trap enabling quantitative analyses of the changes in most insect taxa, and in a long time-span (1992–2005) in a set of permanent plots. The study area was located in a subalpine zone in Bavaria, near Laufen (Germany). The restoration process was initiated in 1996 by a cessation of fertilization and reduction of number of mowing to 1–2 per year. The changes in insect density and diversity (number of families) were monitored in ten restored and two reference plots with the aid of a suction trap. The changes in the insect community recorded during 14 years support findings from other studies that response of insect community to restoration process is usually slow on average. The short-term comparison in 2004–2005 between the restored and reference plots show that the first ones were characterized by more diverse (in term of family number) insect communities (as a whole as well as in guilds of predatory and parasitic species). From the other side, the long-term trend analysis shows that since 1998–2000 insect diversity and abundance was declining. Also trophic structure is fluctuating without clearly defined trend. These findings are in line with the results of the analyses of taxonomic composition similarity. They did not support the expectations neither that difference between initial and current taxonomical composition in a restored plot increases in time (mainly because of incoming new species), nor that spatial heterogeneity of insect assemblages should increase. However, spatio-temporal insect interactions between sample plots (located close to each other), linked to high movement ability of many insect taxa, could mask the changes in insect community caused by restoration.

Colonization of a host tree by herbivorous insects under a changing climate

Climate warming has been predicted to increase the abundance of herbivorous insects. Together with concurrent poleward shifts in many insect species this may increase herbivore pressure on plants. However, the manner in which plants at higher latitudes become colonized by herbivorous insects in the future is unknown. We established a translocation experiment using 26 micropropagated silver birch Betula pendula genotypes from six populations originating from 60°N to 67°N, to study the susceptibility of the translocated birches to local herbivores. The birches were planted at three different latitudes in Finland (60°N, 62°N and 67°N). We studied the effect of source population and latitudinal translocation on herbivore density, species richness, and community composition among the genotypes growing in the same environmental conditions in two years; 2011 and 2012. The source population explained the variation in the herbivore density only in 2012, whereas latitudinal translocation did not affect herbivore density. Variation in species richness was not explained by the source population or by the latitudinal translocation. At two of the study sites, the similarity of the herbivore communities among the populations decreased with increasing latitudinal distance of the source populations, possibly because birch populations that grow geographically closer to each other are genetically more similar, and therefore support a more similar composition of the arthropod community. All birch genotypes were colonized by local herbivores, suggesting that as herbivores shift their ranges polewards, they are able to colonize novel host‐plant genotypes. This enables compositional changes in insect communities on their host plants in the future, which in turn, might affect total herbivory and eventually, plant growth.

비행간섭트랩에 포획된 속리산국립공원내의 송장벌레류 종구성 및 풍부도의 계절적 변동

곤충 군집의 변화는 서식지 환경의 변화를 파악할 수 있는 척도가 된다. 속리산국립공원에서 2003년부터 2007년까지 월별(4월-10월)로 Flight Interception Trap (FIT)을 이용하여 송장벌레류의 종 구성과 풍부도의 변화를 알아보기 위한 조사를 실시하였다. 그 결과, 6종 9,704개체가 조사되었는데, 이 중 넉점박이송장벌레(Nicrophorus quadripunctatus)가 8,763개체(90.3%)로 가장 높은 우점도를 보였다. 넉점박이송장벌레를 제외한 나머지 5종은 971개체(9.7%)에 불과하였다. 송장벌레 6종의 계절적 풍부도 변화에 따르면 7월과 8월이 최성기인 것으로 나타났다. 또한 연간 풍부도는 2004년 이후 점차 감소하는 경향을 보이고 있다. 장기간의 모니터링 결과, 환경지표종으로 활용이 가능한 송장벌레류의 종구성과 풍부도 변화는 속리산의 기후변화를 간접적으로 나타내고 있음을 시사한다. Changes in insect communities are one of the best indicators of environmental changes. A survey was conducted using the Flight Interception Trap (FIT) method to check the changes of species composition and abundance of silphids at Mt. Sokrisan National Park from April to October in 2003 to 2007. A total of 9,704 individuals of six silphid species were examined by FIT. Among them, Nicrophorus quadripunctatus was the most dominant species with 8,763 (90.3%) individuals. There were only 971 (9.7%) individuals of the other five species. The seasonal abundance of silphids peaked in July and August. The annual abundance has decreased gradually since 2004. Therefore, the changing patterns of species composition and abundance of silphids checked by long-term monitoring could be used as environmental indicators which indirectly show the environmental changes of Mt. Sokrisan National Park.

Insects in fragmented forests: a functional approach

Insects are highly susceptible to the adverse effects of forest fragmentation. It is now beyond any doubt that fragmentation-induced changes in abundance and species richness occur in many insect groups. However, the study of insects in fragmented forests is still in its infancy and lacks real direction. Simple empirical studies are not answering the questions we most want to answer about fragmented systems. Are we in the midst of a mass-extinction crisis? What is the functional significance of the immense insect biodiversity? Does biodiversity loss affect ecosystem functioning? A more focused, functional approach to the study of forest fragmentation is required to move beyond the description of pattern and to determine how changes in insect communities affect ecosystem processes in fragmented forests.