TREE SPECIES SUSCEPTIBILITY TO LEAF-CUTTING ANTS ATTACK IN CARBON NEUTRALIZATION PLANTATIONS

Greenhouse gas (GHG) emissions neutralize planting are one of the options for climate changes mitigating. Leaf-cutter ants attack is a threat to the plantations proper development. Ants have selective foraging, which makes it important to know this selectivity and, thus, choose more suitable species to neutralization planting compose. Thus, the goal of the present study was to evaluate the tree species susceptibility to be attacked by leaf-cutter ants in carbon neutralization plantations. The study was carried out in mixed plantations in Viçosa-MG and a classification was created for the present species. The Damage Index (DI) was created by multiplying the Mean of Severity (MS) and the Frequency of Attacks (FA). The species were classified according to the indication for neutralization plantations (indicated, moderately indicated, and not indicated) and potential species for the extraction of natural insecticides. From the 59 species evaluated, 22 were classified as suitable for neutralization plantations, 6 as moderately indicated, 24 as not indicated, and 7 as potential species for extracting natural insecticides. Keywords: forest carbon; pest control; carbon offset; mixed plantings.

The diet of greater crested terns off southeast Australia varies with breeding stage and sea surface temperature

Monitoring seabird diet can provide insights into marine ecosystems that are logistically difficult or costly to observe with traditional fisheries survey methods. Using digital photography, we described the diet of greater crested terns (Thalasseus bergii) breeding on Montague Island (36°15′ S, 150°13′ E), a colony located in an oceanographically dynamic region of southeast Australia. We investigated how the type and size of prey brought back to the colony changed in relation to both breeding stage and variation in local environmental conditions. 2469 prey items were identified to species or family level over 35 consecutive days of photo-sampling in 2018. Australian anchovy (Engraulis australis), a surface-schooling clupeid fish, was the most abundant prey returned to the colony during all breeding stages (84.5%). The proportion of anchovy increased from 77.0% when birds were provisioning their adult partners during incubation, to 92.4% when they were provisioning chicks, suggesting selective foraging behaviour on this energy-rich species to facilitate rapid chick growth. Anchovy size was significantly larger during incubation (91.1 ± 14.9 mm), smaller during early chick provisioning (71.8 ± 11.0 mm), and increased slightly during mid provisioning (79.6 ± 11.9 mm), indicating adaptive prey selection that is matched to the physical requirements of different breeding stages. The proportion of anchovy prey was also influenced by sea surface temperature (SST), with anchovy becoming more dominant with increasing local SSTs, up to ~ 17.5 °C. This study gives new insight into the types of prey that are seasonally available to predators in this region. The strong specialisation by greater crested terns for one energy-rich species of schooling fish (anchovy) suggests that variation in the size and composition of their prey may serve as an indicator of change in the pelagic ecosystem off southeast Australia.

Cross-Ecosystem Linkages: Transfer of Polyunsaturated Fatty Acids From Streams to Riparian Spiders via Emergent Insects

Polyunsaturated fatty acids (PUFAs) are essential resources unequally distributed throughout landscapes. Certain PUFAs, such as eicosapentaenoic acid (EPA), are common in aquatic but scarce in terrestrial ecosystems. In environments with low PUFA availability, meeting nutritional needs requires either adaptations in metabolism to PUFA-poor resources or selective foraging for PUFA-rich resources. Amphibiotic organisms that emerge from aquatic ecosystems represent important resources that can be exploited by predators in adjacent terrestrial habitats. Here, we traced PUFA transfer from streams to terrestrial ecosystems, considering benthic algae as the initial PUFA source, through emergent aquatic insects to riparian spiders. We combined carbon stable isotope and fatty acid analyses to follow food web linkages across the ecosystem boundary and investigated the influence of spider lifestyle (web building vs. ground dwelling), season, and ecosystem degradation on PUFA relations. Our data revealed that riparian spiders consumed considerable amounts of aquatic-derived resources. EPA represented on average 15 % of the total fatty acids in riparian spiders. Season had a strong influence on spider PUFA profiles, with highest EPA contents in spring. Isotope data revealed that web-building spiders contain more aquatic-derived carbon than ground dwelling spiders in spring, although both spider types had similarly high EPA levels. Comparing a natural with an anthropogenically degraded fluvial system revealed higher stearidonic acid (SDA) contents and Σω3/Σω6 ratios in spiders collected along the more natural river in spring but no difference in spider EPA content between systems. PUFA profiles of riparian spiders where distinct from other terrestrial organism and more closely resembled that of emergent aquatic insects (higher Σω3/Σω6 ratio). We show here that the extent to which riparian spiders draw on aquatic PUFA subsidies can vary seasonally and depends on the spider’s lifestyle, highlighting the complexity of aquatic-terrestrial linkages.

As the prey thickens: rainbow trout select prey based upon width not length

Drift-feeding fish are typically considered size-selective predators. Yet, few studies have explicitly tested which aspect of prey “size” best explains size selection by drift-foraging fish. Here, we develop a Bayesian discrete choice model to evaluate how attributes of both prey and predator simultaneously influence size-selective foraging. We apply the model to a large dataset of paired invertebrate drift (n = 784) and rainbow trout (Oncorhynchus mykiss) diets (n = 1028). We characterized prey “size” using six metrics (length, width, area, hemispherical area, volume, mass) and used pseudo-R2 to determine which metric best explained observed prey selection across seven taxa. We found that rainbow trout are positively size-selective, they are selecting prey based upon differences in prey width, and size-selectivity increases with fish length. Rainbow trout demonstrated strong selection for the adult and pupae stages of aquatic insects relative to their larval stages. Our study provides strong empirical evidence for size-selective foraging in rainbow trout and demonstrates prey selection is based primarily upon width, not length or area as has been widely reported.

Breeding Stage and Environmental Factors Affect Prey Selection by Greater Crested Terns Off Southeast Australia

Variation in the diet of marine predators such as seabirds can be used to track environmentally-driven changes in ocean ecosystems. However, studies of predator diet must account for intrinsic influences on prey selection, such as changing nutritional requirements during breeding. Using digital photography, we investigated how the type and size of prey brought back to the colony by greater crested terns (Thalasseus bergii) changed in relation to breeding stage, and to variation in oceanographic conditions around Montague Island, Australia (36°15’S, 150°13’E). 2469 prey items were identified to species or family level over 35 consecutive days of photo-sampling in 2018. Australian anchovy (Engraulis australis), a surface-schooling clupeid fish, was the most abundant prey returned to the colony during all breeding stages (84.5%). The proportion of anchovy increased from 77.0% when birds were provisioning their adult partners during incubation, to 92.4% when they were provisioning chicks, suggesting selective foraging behaviour on this energy-dense species as a means to facilitate rapid chick growth. Anchovy size was largest during incubation (91.1 ± 14.9 mm), smallest during early chick provisioning (71.8 ± 11.0 mm), and increased slightly during mid-provisioning (79.6 ± 11.9 mm), indicating adaptive prey selection that is matched to the physical requirements of different breeding stages. The proportion of anchovy prey was also influenced by extrinsic environmental factors, with anchovy becoming more dominant with increasing local sea surface temperatures, up to ~17.5°C. Our findings highlight the importance of examining both intrinsic and extrinsic determinants of diet composition across breeding stages in seabird populations.

Macropods, feral goats, sheep and cattle: 1. Equivalency in how much they eat

The extent to which goats and cattle eat equivalent amounts of forage as sheep has been based on their maintenance energy requirements (MERs) relative to a 50kg wether or dry ewe, known as a dry sheep equivalent (DSE). As such, a 50kg goat was considered 1 DSE and a 450kg steer as 7–8 DSE. In comparison, the DSE of macropods has been based on their basal metabolic rate (BMR) or energy expenditure of grazing (EEg) relative to those of sheep, with a 50kg macropod thought to be 0.7 and 0.45 DSE respectively. Based on published energy requirements of goats, macropods and cattle relative to sheep, their DSE values are estimated to be 1.2, 1.0 and 7.6 respectively. However, relative energy requirements may not be the same as relative dry matter intakes (DMIs), due to differences in forage quality, the structure of digestive tracts and selective foraging capabilities. Allometric equations that predict DMI were developed from published liveweights and intakes of sheep, goats, macropods and cattle. Given DMIs when fed high-quality forage, a 50kg goat was 1 DSE, a 50kg macropod was 0.7 DSE and a 450kg steer was 7.6 DSE. Their DMIs were depressed by 35–50% when fed low-quality forage, but a goat remained as 1 DSE, macropods increased to 1.0 DSE and cattle increased to 8.3 DSE. The capacity of macropods to maintain relatively higher DMIs of low-quality forage than sheep is probably due of their faster digesta passage rates and more expandable stomachs. These DMIs of animals provided ad-libitum quantities of similar forages in small pens are likely to differ from their DMIs when selectively grazing heterogeneous rangeland pastures. Under these conditions, sheep select higher-quality diets than cattle, and kangaroos select higher-quality diets than sheep, which increase the relative DMIs of the smaller herbivores. For this reason, a 50kg macropod is likely to be 1 DSE and consume twice as much forage than previously assumed.