The paper by Hallmann et. al. studied insect biomass in nature-protected areas in Germany over a period of 27 years. They didn't refer to "habitat loss" in thei

The paper by Hallmann et. al. studied insect biomass in nature-protected areas in Germany over a period of 27 years. They didn't refer to "habitat loss" in their paper, but do refer to "land use" as a broader generalization describing the overall biodiversity of foliage in areas surrounding the insect traps. They measured a number of variables during the study (different aspects of weather and climate and land use), but failed to find a single explanatory variable to match the trend they were seeing. They proposed that the cause was something they weren't measuring. Abstract: "We show that this decline is apparent regardless of habitat type, while changes in weather, land use, and habitat characteristics cannot explain this overall decline." Results: "There was substantial variation in trapped insect biomass between habitat clusters (see Materials and methods), with nutrient-rich grasslands, margins and wasteland containing 43% more insect biomass than nutrient-poor heathland, sandy grassland, and dunes. Yet, the annual rate of decline was similar, suggesting that the decline is not specific to certain habitat types (S5 Fig)." "On average, cover of arable land decreased, coverage of forests increased, while grassland and surface water did not change much in extent over the last three decades (S3 Fig). Overall, adding land use variables alone did not lead to a substantial improvement of the model fit..." "These interactions, which were retained in our final model (Table 4), revealed higher rates of decline where coverage of grassland was higher, while lower declines where forest and arable land coverage was higher." Discussion: "In light of previously suggested driving mechanisms, our analysis renders two of the prime suspects, i.e. landscape [9, 18, 20] and climate change [15, 18, 21, 37], as unlikely explanatory factors for this major decline in aerial insect biomass in the investigated protected areas." "Agricultural intensification [17, 20] (e.g. pesticide usage, yearround tillage, increased use of fertilizers and frequency of agronomic measures) that we could not incorporate in our analyses, may form a plausible cause. The reserves in which the traps were placed are of limited size in this typical fragmented West-European landscape, and almost all locations (94%) are enclosed by agricultural fields. Part of the explanation could therefore be that the protected areas (serving as insect sources) are affected and drained by the agricultural fields in the broader surroundings (serving as sinks or even as ecological traps)." i.e., they're finding that habitat type is insufficiently correlated with the observed effects, and suggesting that some other effect related to nearby agriculture is the predominant cause. The paper is free to download and very readable: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0185809 http://journals.plos.org/plosone/article?id=10.1371/journal....