Top–down limits on prey populations may be more severe in larger prey species, despite having fewer predators

The dependency of mustelid demographic rates on prey abundance has the potential to cause a strong coupling between predator-prey populations. Data on mustelid dynamics show that such strong reciprocal interactions only materialise in some restricted conditions. Bite-size mustelid predators searching for scarce, depleted prey expose themselves to increased risk of predation by larger predators of small mammal that are themselves searching for similar prey species. As voles or muskrats become scarcer, weasels and mink searching for prey over larger areas become increasingly exposed to intra-guild predation, unless they operate in a habitat refuge such as the sub-nivean space. Where larger predators are sufficiently abundant or exert year-round predation pressure on small mustelids, their impact on mustelids may impose biological barrier to dispersal that are sufficient to weaken the coupling between small mustelids and their rodent prey, and thus impose a degree of top down limitation on mustelids.

Using BAD for good: how best available data facilitated a precautionary policy change to improve protection of the prey of the tiger Panthera tigris in Malaysia

Oryx ◽

10.1017/s0030605312000294 ◽

2013 ◽

Vol 47 (3) ◽

pp. 420-426 ◽

Cited By ~ 8

Author(s):

Kae Kawanishi ◽

Gopalasamy Reuben Clements ◽

Melvin Gumal ◽

Gareth Goldthorpe ◽

Mohd Nawayai Yasak ◽

...

Keyword(s):

Prey Species ◽

Action Plan ◽

Legal Protection ◽

Camera Trapping ◽

Panthera Tigris ◽

Policy Changes ◽

Illegal Hunting ◽

Tapirus Indicus ◽

Prey Populations

AbstractTiger Panthera tigris populations are under threat from poaching and depletion of their prey populations. The National Tiger Action Plan for Malaysia contains several actions addressing the threat of legal and illegal hunting of tiger prey species. One action in this plan required an investigation of whether urgent policy changes were needed to improve the protection of the prey of tigers, based on existing data. As the lack of reliable baseline data prevented us from determining population trends accurately, we compiled camera-trapping data from 23 studies conducted between 1997 and 2008 on four principal tiger prey species (sambar Rusa unicolor, barking deer Muntiacus muntjac, wild boar Sus scrofa and bearded pig S. barbatus) and two potential prey species (gaur Bos gaurus and Malayan tapir Tapirus indicus) and compared their distributions and relative abundances. From 10,145 wildlife photographs spanning 40,303 trap-nights, sambar, bearded pig and gaur appeared to be most threatened given their restricted distribution and low relative abundance. Among these, the gaur has full legal protection and has received more conservation attention than the other two species. Following our assessment and advocacy a 6-year moratorium on hunting both sambar and barking deer was imposed by the Malaysian government and the highest protection status possible was afforded the bearded pig. This case study illustrates how best available data (BAD), in this case from camera-trapping studies, can be harnessed to effect precautionary policy changes to curb the impacts of hunting on threatened predator and prey populations that could crash well before resources would otherwise be available for rigorous scientific assessments.

Raptor Prey Remains

10.53061/njzi5339 ◽

2020 ◽

Author(s):

Ed Drewitt

Keyword(s):

Feeding Ecology ◽

Prey Species ◽

Local Level ◽

Body Parts ◽

Change Over Time ◽

The Common ◽

Prey Remains ◽

Over Time ◽

Prey Populations

Are you curious about the remains of an animal you have found? This compilation of the most likely found body parts of animals eaten by raptors will help you identify your discovery. Including over 100 species of bird and mammal prey of raptors such as sparrowhawks, peregrines and hen harriers, this photographic guide highlights the common feathers, fur and other body parts found at raptor nests, roosts, plucking posts and other opportunistic spots. Discovering what raptors eat is an important part of confirming their feeding ecology and how this might change over time, vary on a local level or in response to changing prey populations, as well as dispelling myths and assumptions about what certain raptor species eat. Diet studies are vital for the conservation of raptor species; the more we know about what they need for survival the more we can predict and plan long-term for the protection and survival of raptors that may be vulnerable and in decline. This is the first book to show in detail the actual parts of a bird, mammal or other animal that you are likely to find in a garden, woodland or beneath a raptor roost. As more people take an interest in raptors and watch species such as peregrines via webcams and through watch groups, there is greater opportunity for finding prey remains. This book provides the first and most important step in identifying a prey species.

Evidence that population increase and range expansion by Eurasian Sparrowhawks has impacted avian prey populations

10.1101/491522 ◽

2018 ◽

Cited By ~ 1

Author(s):

Christopher Paul Bell

Keyword(s):

Range Expansion ◽

Census Data ◽

Prey Species ◽

Site Occupancy ◽

Population Increase ◽

Substantial Impact ◽

Bird Populations ◽

General Decline ◽

The Impact ◽

Prey Populations

AbstractThe role of increased predator numbers in the general decline of bird populations in the late 20th century remains controversial, particularly in the case of the Eurasian Sparrowhawk, for which there are contradictory results concerning its effect on the abundance of potential prey species. Previous studies of breeding season census data for Sparrowhawks and prey species in Britain have measured predator abundance either as raw presence-absence data or as an estimate derived from spatially explicit modelling, and have found little evidence of association between predator and prey populations. Here, a predator index derived from site-level binary logistic modelling was used in a regression analysis of breeding census data on 42 prey species, with significant effects emerging in 27 species (16 positive, 11 negative). The frequency of significant positive associations may indicate the tracking of prey abundance by Sparrowhawks, which would tend to cancel out any negative predation effect on prey populations, rendering it difficult to detect using census data. If so, the negative effects that have emerged for some species may underestimate the impact of increased Sparrowhawk numbers on the prey populations concerned. Nevertheless, estimates of the effect on national populations of prey species, obtained by combining effect sizes with a measure of the increase in site occupancy by the predator, suggest the possibility of a substantial impact. It cannot, therefore, be ruled out that the increase in abundance and range expansion of Sparrowhawks made a significant contribution to contemporaneous declines in the populations of many of its prey species.

Intraguild predation and competition: an analysis of net growth shifts in larval amphibian prey

Canadian Journal of Zoology ◽

10.1139/z88-262 ◽

1988 ◽

Vol 66 (8) ◽

pp. 1813-1821 ◽

Cited By ~ 16

Author(s):

Spencer A. Cortwright

Keyword(s):

Intraguild Predation ◽

Prey Species ◽

Negative Impact ◽

Growth Responses ◽

Ambystoma Jeffersonianum ◽

Natural Pond ◽

Resource Levels ◽

Experimental Treatments ◽

Salamander Larvae ◽

Prey Populations

This study examines the net shift in prey growth among species of aquatic salamander larvae (Ambystoma) that engage in intraguild prédation and competition with their predators. Larval salamander and frog species were studied in a pen experiment in a natural pond. A 2 × 3 factorial experimental design was used. The factors were (i) the presence (11 per pen) or absence of Ambystoma opacum predators, and (ii) three levels of Ambystoma jeffersonianum (42, 84, and 168 per pen), a prey species that also shares resources with A. opacum. All other species were stocked at constant levels. Mass at metamorphosis of A. jeffersonianum was not affected by predator presence. The larval period of A. jeffersonianum (prey) decreased by 20 d in the presence of A. opacum (predators), suggesting enhanced differentiation rate when predators reduced prey populations. Ambystoma maculatum (another prey species) showed no growth responses across experimental treatments, probably because it faced predation from both A. opacum and A. jeffersonianum. A previous study showed that in the absence of both A. opacum and A. jeffersonianum predators, A. maculatum prey manifested reduced mass at metamorphosis. Thus, among these predators and prey, which share resources, the enhanced differentiation rate or larger metamorphic size that prey experienced in reduced prey populations was more important than any negative impact of depressed shared resource levels among predators and prey.

High moon brightness and low ambient temperatures affect sloth predation by harpy eagles

PeerJ ◽

10.7717/peerj.9756 ◽

2020 ◽

Vol 8 ◽

pp. e9756 ◽

Cited By ~ 1

Author(s):

Everton B.P. de Miranda ◽

Caio F. Kenup ◽

Edwin Campbell-Thompson ◽

Felix H. Vargas ◽

Angel Muela ◽

...

Keyword(s):

Body Temperature ◽

Tropical Forests ◽

Life Histories ◽

Prey Species ◽

Core Body Temperature ◽

Climatic Conditions ◽

Seasonal Effects ◽

Top Down ◽

Predator Prey ◽

Ambient Temperatures

Background Climate plays a key role in the life histories of tropical vertebrates. However, tropical forests are only weakly seasonal compared with temperate and boreal regions. For species with limited ability to control core body temperature, even mild climatic variation can determine major behavioural outcomes, such as foraging and predator avoidance. In tropical forests, sloths are the arboreal vertebrate attaining the greatest biomass density, but their capacity to regulate body temperature is limited, relying on behavioural adaptations to thermoregulate. Sloths are largely or strictly nocturnal, and depend on crypsis to avoid predation. The harpy eagle (Harpia harpyja) is a sloth-specialist and exerts strong top-down control over its prey species. Yet the role of environmental variables on the regulation of predator–prey interactions between sloths and harpy eagles are unknown. The harpy eagle is considered Near Threatened. This motivated a comprehensive eﬀort to reintroduce this species into parts of Mesoamerica. This eﬀort incidentally enabled us to understand the prey profile of harpy eagles over multiple seasons. Methods Our study was conducted between 2003 and 2009 at Soberanía National Park, Panamá. Telemetered harpy eagles were seen hunting and feeding on individual prey species. For each predation event, field assistants systematically recorded the species killed. We analysed the effects of climatic conditions and vegetation phenology on the prey species profile of harpy eagles using generalised linear mixed models. Results Here we show that sloth predation by harpy eagles was negatively aﬀected by nocturnal ambient light (i.e. bright moonshine) and positively aﬀected by seasonally cool temperatures. We suggest that the first ensured low detectability conditions for sloths foraging at night and the second posed a thermally unsuitable climate that forced sloths to forage under riskier daylight. We showed that even moderate seasonal variation in temperature can influence the relationship between a keystone tropical forest predator and a dominant prey item. Therefore, predator–prey ecology in the tropics can be modulated by subtle changes in environmental conditions. The seasonal eﬀects shown here suggest important demographic consequences for sloths, which are under top-down regulation from harpy eagle predation, perhaps limiting their geographic distribution at higher latitudes.

Inter-specific competition influences apex predator–prey populations

Wildlife Research ◽

10.1071/wr19011 ◽

2019 ◽

Vol 46 (7) ◽

pp. 628

Author(s):

Chidanand S. Reddy ◽

Reuven Yosef ◽

Gianpiero Calvi ◽

Lorenzo Fornasari

Keyword(s):

Growth Rate ◽

Species Interactions ◽

Prey Species ◽

Predation Pressure ◽

Panthera Tigris ◽

Predator Prey ◽

Cuon Alpinus ◽

Prey System ◽

Tiger Reserve ◽

Prey Populations

Abstract ContextTiger (Panthera tigris), leopard (Panthera pardus) and dhole (Cuon alpinus) represent a typical multi-predator system of species of conservation concern. Several studies have addressed this system, with heterogeneous results, and there’s a lack of information on population dynamics of multi-species assemblages. We studied a time series (1998–2009) of abundance indices for three predators and five prey species in Bor Wildlife Sanctuary (BWS), Maharashtra, India, before it was declared as Bor Tiger Reserve (BTR) in 2009. AimsTo analyse the complex relationships within a predator–prey system in a dynamic fashion, to analyse data collected in a stable and undisturbed area and to form a comparison basis for future studies within the sanctuary after its declaration as a Tiger Reserve. MethodsA 24-h effort was made annually to census the BWS. Predators were counted at waterholes from arboreal hideouts. The prey populations were censused along 353-km line-transects. For each species, we analysed the yearly growth rate, testing the effect of inter-species abundance. Key resultsTiger growth rate did not depend on any particular prey, whereas mesopredators seemed to depend on medium-sized prey. A die-out of dholes in 2001 was followed by an increase in tiger populations (from 4 to 11), which, in turn, negatively affected leopard numbers (from 6 to 2).We found no direct evidence of top-down effect, but the density dependence for three of five prey species could be linked to predation pressure. We found some evidence of interspecific competition among prey species, especially among ungulates, potentially being mediated by predation pressure. ConclusionsThe relationships among species in a predator–prey system are very complex and often could be explained only by more-than-two-species interactions. The disappearance of one predator, not necessarily the top predator, could bring multiple effects, for which it could be difficult to detect causal relationships. ImplicationsAll subsequent changes in human activities in the sanctuary, as a consequence of its designation as the BTR in 2009, should be evaluated with respect to the results of the present study. The conservation of large predators should rely on the maintenance of a rich and abundant prey base, in which different-sized prey could lessen interactive-competition among the predators.

Top-Down Processing and Visual Reorientation Illusions in a Virtual Reality Environment

Swiss Journal of Psychology ◽

10.1024/1421-0185.63.3.143 ◽

2004 ◽

Vol 63 (3) ◽

pp. 143-149 ◽

Cited By ~ 3

Author(s):

Fred W. Mast ◽

Charles M. Oman

Keyword(s):

Virtual Reality ◽

Visual Processing ◽

Line Length ◽

Perceptual Cues ◽

Virtual Reality Environment ◽

Top Down ◽

Test Conditions ◽

The Subject ◽

Processing Mechanisms

The role of top-down processing on the horizontal-vertical line length illusion was examined by means of an ambiguous room with dual visual verticals. In one of the test conditions, the subjects were cued to one of the two verticals and were instructed to cognitively reassign the apparent vertical to the cued orientation. When they have mentally adjusted their perception, two lines in a plus sign configuration appeared and the subjects had to evaluate which line was longer. The results showed that the line length appeared longer when it was aligned with the direction of the vertical currently perceived by the subject. This study provides a demonstration that top-down processing influences lower level visual processing mechanisms. In another test condition, the subjects had all perceptual cues available and the influence was even stronger.

Functional Anatomy of Intensity Aspects of Attention

Zeitschrift für Neuropsychologie ◽

10.1024/1016-264x.14.3.181 ◽

2003 ◽

Vol 14 (3) ◽

pp. 181-190 ◽

Cited By ~ 2

Author(s):

Walter Sturm

Keyword(s):

Right Hemisphere ◽

Functional Anatomy ◽

Fmri Data ◽

Functional Networks ◽

Top Down ◽

Stimulus Modality ◽

Spatial Orienting ◽

Phasic Alertness ◽

Co Activation ◽

Attention System

Abstract: Behavioral and PET/fMRI-data are presented to delineate the functional networks subserving alertness, sustained attention, and vigilance as different aspects of attention intensity. The data suggest that a mostly right-hemisphere frontal, parietal, thalamic, and brainstem network plays an important role in the regulation of attention intensity, irrespective of stimulus modality. Under conditions of phasic alertness there is less right frontal activation reflecting a diminished need for top-down regulation with phasic extrinsic stimulation. Furthermore, a high overlap between the functional networks for alerting and spatial orienting of attention is demonstrated. These findings support the hypothesis of a co-activation of the posterior attention system involved in spatial orienting by the anterior alerting network. Possible implications of these findings for the therapy of neglect are proposed.

Auswirkungen eines Aufmerksamkeitstrainings auf die aphasische Symptomatik bei Schlaganfallpatienten

Zeitschrift für Neuropsychologie ◽

10.1024/1016-264x/a000027 ◽

2011 ◽

Vol 22 (1) ◽

pp. 21-32 ◽

Cited By ~ 2

Author(s):

Julia Graf ◽

Hartwig Kulke ◽

Christa Sous-Kulke ◽

Wilfried Schupp ◽

Stefan Lautenbacher

Keyword(s):

Top Down

Aufmerksamkeit kann als Kontrollsystem neuronaler Aktivität verstanden werden, welches Neuroplastizität top-down modulieren hilft. Bisher wurde selten versucht, durch deren gezielte Förderung Funktionswiederherstellungen nach Hirnschädigung zu begünstigen. In vorliegender Studie wurde dies am Beispiel der Aphasie erprobt. 15 Schlaganfallpatienten erhielten ein dreiwöchiges Training der selektiven Aufmerksamkeit mit den PC-Programmen CogniPlus und „Konzentration“ bei fünf Sitzungen pro Woche zusätzlich zur Standardtherapie, 13 weitere bildeten eine Kontrollgruppe ohne Aufmerksamkeitstraining. Zur Effektivitätskontrolle dienten zwei Versionen des Untertests Go/Nogo (Testbatterie zur Aufmerksamkeitsprüfung) und die Kurze Aphasieprüfung. Nach dem Training manifestierte sich zwischen den Untersuchungsgruppen kein Unterschied in Aufmerksamkeits- und Sprachfunktionen; das zusätzliche Aufmerksamkeitstraining war also wirkungslos. Allerdings zeigten Patienten mit deutlichen Aufmerksamkeitsverbesserungen tendenziell weniger Aphasie-Symptome, was die Hypothese aufmerksamkeitsvermittelter Plastizitätsmodulation nach Hirnschädigung partiell stützt.