Incorporating anthropogenic effects into trophic ecology: predator-prey interactions in a human-dominated landscape

Apex predators perform important functions that regulate ecosystems worldwide. However, little is known about how ecosystem regulation by predators is influenced by human activities. In particular, how important are top-down effects of predators relative to direct and indirect human-mediated bottom-up and top-down processes? Combining data on species' occurrence from camera traps and hunting records, we aimed to quantify the relative effects of top-down and bottom-up processes in shaping predator and prey distributions in a human-dominated landscape in Transylvania, Romania. By global standards this system is diverse, including apex predators (brown bear and wolf), mesopredators (red fox) and large herbivores (roe and red deer). Humans and free-ranging dogs represent additional predators in the system. Using structural equation modelling, we found that apex predators suppress lower trophic levels, especially herbivores. However, direct and indirect top-down effects of humans affected the ecosystem more strongly, influencing species at all trophic levels. Our study highlights the need to explicitly embed humans and their influences within trophic cascade theory. This will greatly expand our understanding of species interactions in human-modified landscapes, which compose the majority of the Earth's terrestrial surface.

Rearing juvenile Australian native percichthyid fish in fertilised earthen ponds

The post-larvae and fry of Australian native species, including those of species belonging to the family Percichthyidae, are routinely reared to a fingerling size (35-55 mm in length) in fertilised earthen fry rearing ponds. The juveniles of Murray cod (Maccullochella peelii peelii\ trout cod (Maccullochella macquariensis) and Macquarie perch (Macquaria australasicd) (Percichthyidae) are grown in fry rearing ponds at the Marine and Freshwater Resources Institute, Snobs Creek (Vie. Australia) for production of fingerlings for stock enhancement and aquaculture purposes. However, no detailed studies have been undertaken of the productivity of these ponds and factors that influence fish production. An ecologically based study was undertaken to increase the knowledge of pond ecology and dynamics, particularly in relation to the rearing of juvenile Murray cod, trout cod and Macquarie perch in ponds. Over nine consecutive seasons commencing in 1991, water chemistry, plankton, macrobenthos (2 seasons only) and fish were monitored and studied in five ponds located at Snobs Creek. A total of 80 pond fillings were undertaken during the study period. Additional data collected from another 24 pond fillings undertaken at Snobs Creek collected prior to this study were included in some analyses. Water chemistry parameters monitored in the ponds included, temperature, dissolved oxygen pH, ammonia, nitrite, nitrate, orthophosphate and alkalinity. Water chemistry varied spatially (within and between ponds) and temporally (diurnally, daily and seasonally). Liming of ponds increased the total alkalinity to levels that were considered to be suitable for enhancing plankton communities and fish production. Water quality within the ponds for the most part was suitable for the rearing of juvenile Murray cod, trout cod and Macquarie perch, as reflected in overall production (growth, survival and yield) from the ponds. However, at times some parameters reached levels which may have stressed fish and reduced growth and survival, in particular, low dissolved oxygen concentrations (minimum 1.18 mg/L), high temperatures (maximum 34°C), high pH (maximum 10.38) and high unionised ammonia (maximum 0.58 mg/L). Species belonging to 37 phytoplankton, 45 zooplankton and 17 chironomid taxa were identified from the ponds during the study. In addition, an extensive checklist of aquatic flora and fauna, recorded from aquaculture ponds in south-eastern Australia, was compiled. However, plankton and benthos samples were usually numerically dominated by a few species only. Rotifers (especially Filinia, Brachionus, Polyarthra, and Asplanchnd), cladocerans (Moina and Daphnid) and copepods (Mesocyclops and Boeckelld) were most abundant and common in the plankton, while chironomids (Chironomus, Polypedilum, and Prodadius) and oligochaetes were most common and abundant in the benthos. Both abundance and species composition of the plankton and macrobenthos varied spatially (within and between ponds) and temporally (diurnally, daily and seasonally). Chlorophyll a concentrations, which ranged from 1.8 to 184 \ig/L (mean 29.37 ng/L), initially peaked within two weeks of filling and fertilising the ponds. Zooplankton peaked in abundance 2-4 weeks after filling the ponds. The maximum zooplankton density recorded in the ponds was 6,621 ind./L (mean 721 ind./L). Typically, amongst the zooplankton, rotifers were first to develop high densities (2nd-3rd week after filling), followed by cladocerans (2nd-4th week after filling) then copepods (2nd-5th week after filling). Chironomid abundance on average peaked later (during the 5th week after filling). The maximum chironomid density recorded in the ponds was 27,470 ind./m2 (mean 4,379 ind./m2). Length-weight, age-weight and age-length relationships were determined for juvenile Murray cod, trout cod and Macquarie perch reared in ponds. These relationships were most similar for Murray cod and trout cod, which are more closely related phylogenetically and similar morphologically than Macquarie perch. Growth of fish was negatively correlated with both size at stocking and stocking biomass. Stocking density experiments showed that, at higher densities, growth offish was significantly reduced, but survival was not affected. The diets of juvenile Murray cod trout cod and Macquarie perch reared in fry ponds were similar. The cladocerans Moina and Daphnia, adult calanoid and cyclopoid copepods and the chironomids, Chironomus, Polypedilum and Procladius were the most commonly occurring and abundant prey. Selection for rotifers and copepod nauplii was strongly negative for all three species of fish. Size range of prey consumed was positively correlated with fish size for trout cod and Macquarie perch, but not for Murray cod. Diet composition changed as the fish grew. Early after stocking the fish into the ponds, Moina was generally the more common prey consumed, while in latter weeks, copepods and chironomids became more abundant and common in the diet. On a dry weight basis, chironomid larvae were the most important component in the diets of these fish species. Selective feeding by fish on larger planktonic species such as adult copepods and cladocerans, may have influenced the plankton community structure as proposed by the trophic cascade or top -down hypothesis. The proximate composition and energy content of Murray cod, trout cod and Macquarie perch, reared in the ponds did not vary significantly between the species, and few significant changes were observed as the fish grew. These results suggested that the nutrient requirements of these species might not vary over the size range of fish examined. Significant differences in the proximate composition of prey were observed between species, size of species and time of season. The energy content of prey (cladocerans, copepods and chironomids) on a pond basis, was closely related to the abundance of these taxa in the ponds. Data collected from all pond fillings during the present study, along with historical data from pond fillings undertaken prior to this study, were combined in a data matrix and analysed for interactions between pairs of parameters. In particular, interactions between selected water chemistry parameters, zooplankton and chironomid abundance indicators were analysed to identify key factors that influence fish production (growth, survival, condition and yield). Significant correlations were detected between fish production indicators and several water chemistry and biota (zooplankton and chironomids) parameters. However, these were not consistent across all three species of fish. These results indicated that the interactions between water chemistry, biota and fish were complex, and that combinations of these parameters, along with other factors not included in the present study, may influence fish production in these ponds. The present study, showed that more stringent monitoring of fry rearing ponds, especially water quality, zooplankton and benthos communities and fish, combined with an associated increase in understanding of the pond ecosystem, can lead to substantial improvements in pond productivity and associated fish production. In the present study this has resulted in a general increase in fish survival rates, which became less variable or more predictable in nature. The value of such knowledge can provide managers with a more predicative capacity to estimate production of ponds in support of stock enhancement programs and provision of juvenile for aquaculture grow-out.

Predator interactions, mesopredator release and biodiversity conservation

There is growing recognition of the important roles played by predators in regulating ecosystems and sustaining biodiversity. Much attention has focused on the consequences of predator-regulation of herbivore populations, and associated trophic cascades. However apex predators may also control smaller ‘mesopredators’ through intraguild interactions. Removal of apex predators can result in changes to intraguild interactions and outbreaks of mesopredators (‘mesopredator release’), leading in turn to increased predation on smaller prey. Here we provide a review and synthesis of studies of predator interactions, mesopredator release and their impacts on biodiversity. Mesopredator suppression by apex predators is widespread geographically and taxonomically. Apex predators suppress mesopredators both by killing them, or instilling fear, which motivates changes in behaviour and habitat use that limit mesopredator distribution and abundance. Changes in the abundance of apex predators may have disproportionate (up to fourfold) effects on mesopredator abundance. Outcomes of interactions between predators may however vary with resource availability, habitat complexity and the complexity of predator communities. There is potential for the restoration of apex predators to have benefits for biodiversity conservation through moderation of the impacts of mesopredators on their prey, but this requires a whole-ecosystem view to avoid unforeseen negative effects.

‘Nothing has changed since I began.

My eye has permitted no change.

I am going to keep things like this.’

From ‘Hawk Roosting’, by Ted Hughes.

Demonising the dingo : how much wild dogma is enough?

The roles that top predators play in regulating the structure and function of ecosystems have long been controversial. This is particularly the case when predators pose adverse risks for human life and/or economic interests. The critique of literature on dingoes and their ecological roles in Australia provided by Allen et al. (2011) shows that top predators remain a potentially polarising issue. In opposition to Allen et al. we argue that these widespread patterns of species’ abundances, attributed to the effects of dingoes and evident at scales ranging from the foraging behaviour of individuals through to continental scale patterns of species abundances, constitute strong support for the mesopredator release hypothesis and provide evidence that dingoes benefit biodiversity conservation by inducing community wide trophic cascades. Harnessing the positive ecological effects of dingoes while at the same time minimising their impacts on agriculture is a major socio-political challenge in Australia [Current Zoology 57 (5): 668-670].

Top predators as biodiversity regulators : the dingo Canis lupus dingo as a case study

Top-order predators often have positive effects on biological diversity owing to their key functional roles in regulating trophic cascades and other ecological processes. Their loss has been identified as a major factor contributing to the decline of biodiversity in both aquatic and terrestrial systems. Consequently, restoring and maintaining the ecological function of top predators is a critical global imperative. Here we review studies of the ecological effects of the dingo Canis lupus dingo, Australia's largest land predator, using this as a case study to explore the influence of a top predator on biodiversity at a continental scale. The dingo was introduced to Australia by people at least 3500 years ago and has an ambiguous status owing to its brief history on the continent, its adverse impacts on livestock production and its role as an ecosystem architect. A large body of research now indicates that dingoes regulate ecological cascades, particularly in arid Australia, and that the removal of dingoes results in an increase in the abundances and impacts of herbivores and invasive mesopredators, most notably the red fox Vulpes vulpes. The loss of dingoes has been linked to widespread losses of small and medium-sized native mammals, the depletion of plant biomass due to the effects of irrupting herbivore populations and increased predation rates by red foxes. We outline a suite of conceptual models to describe the effects of dingoes on vertebrate populations across different Australian environments. Finally, we discuss key issues that require consideration or warrant research before the ecological effects of dingoes can be incorporated formally into biodiversity conservation programs.

The dingo and biodiversity conservation : response to Fleming et al. (2012)

Several authors have recently argued that dingoes could be used to help conserve biodiversity in Australia. Fleming et al. (2012) [Australian Mammalogy 34, 119–131] offer the alternative view that restoration of dingo predation is unlikely to help native species, and is more likely to do harm. We think many of the arguments used by Fleming et al. to reach that conclusion are either unsound or beside the point, and we explain why.

Multiple threats, or multiplying the threats? Interactions between invasive predators and other ecological disturbances

Invasive species have reshaped the composition of biomes across the globe, and considerable cost is now associated with minimising their ecological, social and economic impacts. Mammalian predators are among the most damaging invaders, having caused numerous species extinctions. Here, we review evidence of interactions between invasive predators and six key threats that together have strong potential to influence both the impacts of the predators, and their management. We show that impacts of invasive predators can be classified as either functional or numerical, and that they interact with other threats through both habitat- and community-mediated pathways. Ecosystem context and invasive predator identity are central in shaping variability in these relationships and their outcomes. Greater recognition of the ecological complexities between major processes that threaten biodiversity, including changing spatial and temporal relationships among species, is required to both advance ecological theory and improve conservation actions and outcomes. We discuss how novel approaches to conservation management can be used to address interactions between threatening processes and ameliorate invasive predator impacts.

Preference for feeding at habitat edges declines among juvenile blue crabs as oyster reef patchiness increases and predation risk grows

Both habitat patchiness and behaviorally-mediated indirect effects (BMIEs; predator- induced changes in prey behavior that affect the prey's resources) are important in many food webs, but the relationships between these 2 factors have yet to be investigated. To explore effects of habitat patchiness and variation in perceived risk of predation on food-web dynamics, we conducted a factorial experiment in a model aquatic food chain of predator-prey-resource using 2 contrasting predators (adult blue crab Callinectes sapidus and toad fish Opsanus tau), juvenile blue crab as prey, and mussel Geukensia demissa as resource. Both predator presence and habitat patchiness influenced the prey's preference for consuming resources at patch edges instead of interiors. The preference of prey for consuming resources at habitat edges was 4 times stronger in continuous oyster reef habitat than in smaller habitat patches. This suggests that interior resources in continuous habitat experience a refuge from consumption, but this refuge is largely lost in patchy habitat. The mere presence of predators reduced the prey's preference for consuming resources at habitat edges. This BMIE was significant for the ambush predator (toadfish) and the treatment containing both predators, but not for the actively hunting predator (adult blue crab). We conclude that habitat patchiness and predator presence can jointly affect resource distribution by inducing shifts in prey foraging behavior, revealing a need to incorporate BMIEs into habitat fragmentation studies. This conclusion has broad and growing relevance as anthropogenic factors increasingly modify predator abundances and fragment coastal habitats. © Inter-Research 2012.

Stop jumping the gun : a call for evidence-based invasive predator management

Invasive mammalian predators are major drivers of species extinctions globally. To protect native prey, lethal control is often used with the aim of reducing or exterminating invasive predator populations. The efficacy of this practice, however, is often not considered despite multiple practical and ecological factors that can limit success. Here, we summarize contemporary knowledge regarding the use and challenges of both lethal control and alternative approaches for reducing invasive predator impacts. As the prevailing management approach, we outline four key issues that can compromise the effectiveness of lethal control: release of herbivore and mesopredator populations, disruption of predator social systems, compensatory predator immigration, and ethical concerns. We then discuss the relative merits and limitations of four alternative approaches that may enhance conservation practitioner's ability to effectively manage invasive predators: top-predator conservation or reintroduction, maintaining habitat complexity, exclusion fencing, and behavioral and evolutionary ecology. Considerable uncertainty remains regarding the effectiveness of management approaches in different environmental contexts. We propose that the deficiencies and uncertainties outlined here can be addressed through a combination of adaptive management, expert elicitation, and cost-benefit analyses. Improved management of invasive predators requires greater consideration and assessment of the full range of management approaches available.

Invasive predators and global biodiversity loss.

Invasive species threaten biodiversity globally, and invasive mammalian predators are particularly damaging, having contributed to considerable species decline and extinction. We provide a global metaanalysis of these impacts and reveal their full extent. Invasive predators are implicated in 87 bird, 45 mammal, and 10 reptile species extinctions-58% of these groups' contemporary extinctions worldwide. These figures are likely underestimated because 23 critically endangered species that we assessed are classed as "possibly extinct." Invasive mammalian predators endanger a further 596 species at risk of extinction, with cats, rodents, dogs, and pigs threatening the most species overall. Species most at risk from predators have high evolutionary distinctiveness and inhabit insular environments. Invasive mammalian predators are therefore important drivers of irreversible loss of phylogenetic diversity worldwide. That most impacted species are insular indicates that management of invasive predators on islands should be a global conservation priority. Understanding and mitigating the impact of invasive mammalian predators is essential for reducing the rate of global biodiversity loss.

Trophic responses to nutrient enrichment in a temperate seagrass food chain

Simple ecological models that predict trophic responses to bottom-up forcing are valuable tools for ecosystem managers. Traditionally, theoretical ecologists have used resource-dependent functional responses to explain the modification of food chains exposed to bottom-up perturbations. These models predict alternating positive, negative and zero responses at each trophic level. More recently, ratio-dependent functional response models that predict proportional increases at each level have challenged this paradigm. The present study tested the predictions of the 2 hypotheses empirically by comparing the relative biomasses of 4 trophic levels of an estuarine seagrass food chain in relatively undisturbed, low-nutrient catchments and ‘developed’ catchments subjected to a prolonged period of nutrient enrichment. We found that nutrient-enriched sites had significantly greater biomass of both epiphytic algae and grazing invertebrates; however, the bottom-up forcing of nutrients was attenuated at higher trophic levels (occupied by juvenile and piscivorous fish), with no significant effect of catchment development. This disconnect in the upward cascade of energy may be due to a number of possible reasons including high levels of diversity and omnivory, trophic subsidy within the system or the strength or nature of perturbations. Although the predictions of both hypotheses failed to hold across all trophic groups, ratio dependence was prevalent at the lower levels of the food chain, which has implications for catchment management.

Cold rolling mill thickness control using the cascade-correlation neural network

The improvements in thickness accuracy of a steel strip produced by a tandem cold-roIling mill are of substantial interest to the steel industry. In this paper, we designed a direct model-reference adaptive control (MRAC)  scheme that exploits the natural level of excitation existing in the closed-loop with a dynamically constructed cascade-correlation neural network (CCNN) as a controller for cold roIling mill thickness control. Simulation results show that the combination of a such a direct MRAC scheme and the dynamically constructed CCNN significantly improves the thickness accuracy in the presence of disturbances and noise in comparison with to the conventional PID controllers.

Trophic classification of non-perennial reservoirs utilized for the development of culture-based fisheries, Sri Lanka

The aim of this study was to check the suitability of some trophic models developed for temperate regions to classify the non-perennial reservoirs of Sri Lanka in order to manage culture-based fisheries of those reservoirs. A limnological study was carried out in 45 non-perennial reservoirs, which have been randomly selected for stocking of fish fingerlings for the development of culture-based fisheries. High total phosphorous (TP) content in relation to algal biomass indicates high non-algal turbidity in all reservoirs. Carlson's trophic state indices (TSI) measured on the basis of Secchi disc depth [TSI (SDD)], TP [TSI (TP)] and chlorophyll a [TSI (Chl-a)] show that the 45 reservoirs studied are characterized by TSI (TP) = TSI (SDD) > TSI (Chl-a), indicating that non-algal particulate matter or colour dominates underwater light attenuation. As TSI (Chl-a) is positively correlated to culture-based fisheries yield, it is useful for planning culture-based fisheries development strategies in non-perennial reservoirs of Sri Lanka, and has the potential to be used elsewhere in the tropics for comparable developments.

Algebraic attacks on clock-controlled cascade ciphers

In this paper, we mount the first algebraic attacks against clock controlled cascade stream ciphers. We first show how to obtain relations between the internal state bits and the output bits of the Gollmann clock controlled cascade stream ciphers. We demonstrate that the initial states of the last two shift registers can be determined by the initial states of the others. An alternative attack on the Gollmann cascade is also described, which requires solving quadratic equations. We then present an algebraic analysis of Pomaranch, one of the phase two proposals to eSTREAM. A system of equations of maximum degree four that describes the full cipher is derived. We also present weaknesses in the filter functions of Pomaranch by successfully computing annihilators and low degree multiples of the functions.