Comparing floral resource maps and land cover maps to predict predators and aphid suppression on field bean

Context Predatory insects contribute to the natural control of agricultural pests, but also use plant pollen or nectar as supplementary food resources. Resource maps have been proposed as an alternative to land cover maps for prediction of beneficial insects. Objectives We aimed at predicting the abundance of crop pest predating insects and the pest control service they provide with both, detailed flower resource maps and land cover maps. Methods We selected 19 landscapes of 500 m radius and mapped them with both approaches. In the centres of the landscapes, aphid predators – hoverflies (Diptera: Syrphidae), ladybeetles (Coleoptera: Coccinellidae) and lacewings (Neuroptera: Chrysopidae) – were surveyed in experimentally established faba bean phytometers (Vicia faba L. Var. Sutton Dwarf) and their control of introduced black bean aphids (Aphis fabae Scop.) was recorded. Results Landscapes with higher proportions of forest edge as derived from land cover maps supported higher abundance of aphid predators, and high densities of aphid predators reduced aphid infestation on faba bean. Floral resource maps did not significantly predict predator abundance or aphid control services. Conclusions Land cover maps allowed to relate landscape composition with predator abundance, showing positive effects of forest edges. Floral resource maps may have failed to better predict predators because other resources such as overwintering sites or alternative prey potentially play a more important role than floral resources. More research is needed to further improve our understanding of resource requirements beyond floral resource estimations and our understanding of their role for aphid predators at the landscape scale.

High Survivorship of First-Generation Monarch Butterfly Eggs to Third Instar Associated with a Diverse Arthropod Community

Based on surveys of winter roost sites, the eastern migratory population of the monarch butterfly (Danaus plexippus) in North America appears to have declined in the last 20 years and this has prompted the implementation of numerous conservation strategies. However, there is little information on the survivorship of first-generation monarchs in the core area of occupancy in Texas, Oklahoma, and Louisiana where overwinter population recovery begins. The purpose of this study was to determine the survivorship of first-generation eggs to third instars at a site in north Texas and to evaluate host plant arthropods for their effect on survivorship. Survivorship to third instar averaged 13.4% and varied from 11.7% to 15.6% over three years. The host plants harbored 77 arthropod taxa, including 27 predatory taxa. Despite their abundance, neither predator abundance nor predator richness predicted monarch survival. However, host plants upon which monarchs survived often harbored higher numbers of non-predatory arthropod taxa and more individuals of non-predatory taxa. These results suggest that ecological processes may have buffered the effects of predators and improved monarch survival in our study. The creation of diverse functional arthropod communities should be considered for effective monarch conservation, particularly in southern latitudes.

An early Miocene extinction in pelagic sharks

Shark populations have been decimated in recent decades because of overfishing and other anthropogenic stressors; however, the long-term impacts of such changes in marine predator abundance and diversity are poorly constrained. We present evidence for a previously unknown major extinction event in sharks that occurred in the early Miocene, ~19 million years ago. During this interval, sharks virtually disappeared from open-ocean sediments, declining in abundance by >90% and morphological diversity by >70%, an event from which they never recovered. This abrupt extinction occurred independently from any known global climate event and ~2 million to 5 million years before diversifications in the highly migratory, large-bodied predators that dominate pelagic ecosystems today, indicating that the early Miocene was a period of rapid, transformative change for open-ocean ecosystems.

How effective are frogs in regulating crop pest population in a natural multi-trophic system??

Potential of frogs as important natural pest control agents has been highlighted earlier. But the effectiveness of frogs in regulating the pest load in intensive agricultural landscape in a multi-trophic system is not clear. We performed controlled field experiment in paddy field with a varying density (observed in high and low agricultural intensity (AI) areas) of a commonly found frog species and compared the pest and pest predator build-up. The consumption rate of the model amphibian was studied using enclosure experiment. The consequent trophic cascade effect of frogs on both crop pest and other arthropod pest predator was analyzed using mathematical population growth models. Although frogs consumed pests, they could not reduce crop pest abundance. Although a lesser frog density found in high AI areas significantly affected the pest predator abundance. Based on the functional response result, mathematical growth models demonstrated that with a constant harvesting factor (Holling Type II) frogs will always have a negative impact on the beneficial natural enemy population due to intraguild predation thereby limiting its potential as a pest regulator. Our study challenges the notion of frogs as an effective pest control agent and argues that increasing habitat diversity might improve overall biological pest suppression.

High Survivorship of First-generation Monarch Butterfly Eggs and Larvae Associated with a Diverse Arthropod Community

The eastern migratory population of the monarch butterfly (Danaus plexippus) in North America has declined by over 80% in the last 20 years, prompting the implementation of numerous conservation strategies. However, there is little information on the survivorship of first-generation monarchs in the core area of occupancy in Texas, Oklahoma, and Louisiana where overwinter population recovery begins. The purpose of this study was to determine the survivorship of first-generation eggs to third instars at a site in north Texas and to evaluate host plant arthropods for their effect on survivorship. Survivorship to third instar averaged 13.4% and varied from 11.7% to 15.6% over three years. The host plants harbored 77 arthropod taxa, including 27 predatory taxa. Despite their abundance, neither predator abundance nor predator richness predicted monarch survival. However, host plants upon which monarchs survived often harbored higher numbers of non-predatory arthropod taxa and more individuals of non-predatory taxa. These results indicate that indirect top-down effects improved monarch survival in our study. The creation of diverse functional arthropod communities should be considered for effective monarch conservation, particularly in southern latitudes.

Harvest and density-dependent predation drive long term population decline in a northern ungulate

The relative effect of top-down versus bottom-up forces in regulating and limiting wildlife populations is an important theme in ecology. Untangling these effects is critical for basic understanding of trophic dynamics and effective management. We examined the drivers of moose abundance by integrating two sets of observations to create one of the largest existing spatiotemporal datasets on ungulate population dynamics globally. We documented a 20% population decline. At high density, moose were regulated by intraspecific competition. Predation primarily limited population growth, except at low density, where it was regulating. Harvest was largely additive and contributed to population decline. Our results provide strong evidence for density dependent predation, highlighting that population dynamics are context dependent and vary strongly across gradients in climate, forest type and predator abundance. These results clarify longstanding questions in population ecology and highlight the complex relationships between natural and human-caused mortality in driving ungulate population dynamics.