scholarly journals How optimal foragers should respond to habitat changes? On the consequences of habitat conversion

2018 ◽  
Author(s):  
Vincent Calcagno ◽  
Frédéric Hamelin ◽  
Ludovic Mailleret ◽  
Frédéric Grognard
Keyword(s):  
Average Rate ◽  
Habitat Modification ◽  
Alternative Form ◽  
Residence Times ◽  
Marginal Value ◽  
Distribution Of Resources ◽  
Habitat Conversion ◽  
Qualitative Responses ◽  
Patch Exploitation ◽  
Rate Of Movement

AbstractThe Marginal Value Theorem (MVT) provides a framework to predict how habitat modifications related to the distribution of resources over patches should impact the realized fitness of individuals and their optimal rate of movement (or patch residence times) across the habitat. Most MVT theory has focused on the consequences of changing the shape of the gain functions in some patches, describing for instance patch enrichment. However an alternative form of habitat modification is habitat conversion, whereby patches are converted from one existing type to another (e.g. closed habitat to open habitat). In such a case the set of gain functions existing in the habitat does not change, only their relative frequencies does. This has received comparatively very little attention in the context of the MVT. Here we analyze mathematically the consequences of habitat conversion under the MVT. We study how realized fitness and the average rate of movement should respond to changes in the frequency distribution of patch-types, and how they should covary. We further compare the response of optimal and non-plastic foragers. We find that the initial pattern of patch-exploitation in a habitat, characterized by the regression slope of patch yields over residence times, can help predict the qualitative responses of fitness and movement rate following habitat conversion. We also find that for some habitat conversion patterns, optimal and non-plastic foragers exhibit qualitatively different responses, and that adaptive foragers can have opposite responses in the early and late phases following habitat conversion. We suggest taking into account behavioral responses may help better understand the ecological consequences of habitat conversion.

scholarly journals Foraging as an evidence accumulation process

2018 ◽  
Author(s):  
Jacob D. Davidson ◽  
Ahmed El Hady
Keyword(s):  
Decision Making ◽  
Diffusion Processes ◽  
Optimal Strategies ◽  
Theoretical Work ◽  
Decision Threshold ◽  
Residence Times ◽  
Marginal Value ◽  
Evidence Accumulation ◽  
Current Resource ◽  
Noisy Measurements

AbstractA canonical foraging task is the patch-leaving problem, in which a forager must decide to leave a current resource in search for another. Theoretical work has derived optimal strategies for when to leave a patch, and experiments have tested for conditions where animals do or do not follow an optimal strategy. Nevertheless, models of patch-leaving decisions do not consider the imperfect and noisy sampling process through which an animal gathers information, and how this process is constrained by neurobiological mechanisms. In this theoretical study, we formulate an evidence accumulation model of patch-leaving decisions where the animal averages over noisy measurements to estimate the state of the current patch and the overall environment. Evidence accumulation models belong to the class of drift diffusion processes and have been used to model decision making in different contexts especially in cognitive and systems neuroscience. We solve the model for conditions where foraging decisions are optimal and equivalent to the marginal value theorem, and perform simulations to analyze deviations from optimal when these conditions are not met. By adjusting the drift rate and decision threshold, the model can represent different “strategies”, for example an increment-decrement or counting strategy. These strategies yield identical decisions in the limiting case but differ in how patch residence times adapt when the foraging environment is uncertain. To account for sub-optimal decisions, we introduce an energy-dependent utility function that predicts longer than optimal patch residence times when food is plentiful. Our model provides a quantitative connection between ecological models of foraging behavior and evidence accumulation models of decision making. Moreover, it provides a theoretical framework for potential experiments which seek to identify neural circuits underlying patch leaving decisions.

scholarly journals AUTOMATIC EXTRACTION OF DUNES FROM GOOGLE EARTH IMAGES NEW APPROACH TO STUDY THE DUNES MIGRATION IN THE LAÂYOUNE CITY OF MOROCCO

2016 ◽  
Vol XLII-2/W1 ◽  
pp. 53-59 ◽  
Author(s):  
D. Dakir ◽  
H. Rhinane ◽  
O. Saddiqi ◽  
E. El Arabi ◽  
L. Baidder
Keyword(s):  
Large Scale ◽  
Average Rate ◽  
Google Earth ◽  
Automatic Extraction ◽  
New Approach ◽  
Analysis Techniques ◽  
North East ◽  
South West ◽  
Barchan Dunes ◽  
Rate Of Movement

In desert environments, the sandy dune movements are considered as the main threat to the livelihoods and productivity of people living in Laâyoune city, South of Morocco. Studying dunes at a large scale requires intensive fieldwork and a huge dataset. But this task is not always easy because of the high cost and the limited availability of data. In this paper we present a new approach to study and evaluate the dune dynamic using Google earth archive image acquired from 2005, 2011, 2012, and 2013. To achieve this goal, an area with 3577 meter square including 40 barchan dunes, were selected, and the barchan dunes were automatically extracted from these images using Geographic Information System (GIS) and spatial analysis techniques provided by image processing software. The result shows not only the dune shape but also direction of dunes movements, and distance separating dunes. The obtained direction is ranging from North east to South west. The average rate of movement of the extracted dunes between 2005 and 2013 was calculated and is estimated at 32m per year. Validation of these dunes movement of the Laâyoune city was confirmed by the field data and previous studies.

scholarly journals Movement of the Ross Ice Shelf Near Scott Base

1961 ◽  
Vol 3 (29) ◽  
pp. 859-866 ◽  
Author(s):  
W. J. P. Macdonald ◽  
T. Hatherton
Keyword(s):  
Ross Sea ◽  
Average Rate ◽  
The South ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
Ross Ice Shelf ◽  
Rate Of Movement

Abstract The rate of movement of the Ross Ice Shelf has been determined at its terminal face to the south-east of Scott Base. An average rate of movement of 23 cm./day in a direction 270° True was determined for the period March 1957 to October 1958. The terminating face of the ice shelf in McMurdo Sound is only about 3 metres thick compared with a thickness of several hundred metres in the Ross Sea. Altimeter heights are used to demonstrate a thinning of the shelf which is attributed to melting from below.

scholarly journals Movement of the Ross Ice Shelf Near Scott Base

1961 ◽  
Vol 3 (29) ◽  
pp. 859-866
Author(s):  
W. J. P. Macdonald ◽  
T. Hatherton
Keyword(s):  
Ross Sea ◽  
Average Rate ◽  
The South ◽  
Ice Shelf ◽  
Mcmurdo Sound ◽  
Ross Ice Shelf ◽  
Rate Of Movement

AbstractThe rate of movement of the Ross Ice Shelf has been determined at its terminal face to the south-east of Scott Base. An average rate of movement of 23 cm./day in a direction 270° True was determined for the period March 1957 to October 1958. The terminating face of the ice shelf in McMurdo Sound is only about 3 metres thick compared with a thickness of several hundred metres in the Ross Sea. Altimeter heights are used to demonstrate a thinning of the shelf which is attributed to melting from below.

Spatial dimension and exploitation dynamics of local fishing grounds by fishers targeting several flatfish species

2011 ◽  
Vol 68 (6) ◽  
pp. 1064-1076 ◽  
Author(s):  
Adriaan D. Rijnsdorp ◽  
Jan Jaap Poos ◽  
Floor J. Quirijns
Keyword(s):  
Search Time ◽  
Threshold Level ◽  
Spatial Dimension ◽  
Catch Rate ◽  
Fishing Ground ◽  
Marginal Value Theorem ◽  
Marginal Value ◽  
Individual Transferable Quota ◽  
Fishing Behavior ◽  
Patch Exploitation

Patch exploitation dynamics, based on individual tow data, provided new insights into the fishing behavior of mixed fisheries. Fishing grounds were determined and their geometry quantified based on the proximity of tow positions. Tows were classified as being part of either searching, sampling, or exploitation behavior based on the intertow distance. Fishers can detect patches of flatfish on a scale of ∼25 nautical miles2. Catch rate during exploitation was 24%–36% above the catch rate while searching, and decreased at a rate of 20%·day–1. Once a patch was found, exploitation occurred until the catch rate dropped below a threshold level. The optimal giving-up catch rate was estimated based on the observed search time, catch rate decline, and range of fishing ground quality. The observed giving-up catch rate was 6%–11% higher than predicted by the marginal value theorem. The discrepancy between the observed and predicted patch leaving decision was consistent with the bias expected in an individual transferable quota (ITQ) management system. Our results provide a basis for interpreting vessel monitoring system (VMS) data and studying the interaction among fishers and between fishers and their resources at the appropriate time and spatial scale.

Instrumental measurement of slippage on the Hayward fault

1966 ◽  
Vol 56 (2) ◽  
pp. 305-316
Author(s):  
Bruce A. Bolt ◽  
Walter C. Marion
Keyword(s):  
Physical Model ◽  
Fault Zone ◽  
Average Rate ◽  
Crystalline Basement ◽  
Local Earthquakes ◽  
Shallow Earthquakes ◽  
Instrumental Measurement ◽  
Strain Release ◽  
Measured Displacement ◽  
Rate Of Movement

abstract A differential transformer has been used as a displacementmeter across a crack in a culvert under the Memorial Stadium, UC Berkeley. The crack is believed to be the result of progressive right-lateral slippage in recent years along the Hayward fault which traverses the stadium. The displacementmeter recorded continuous right-lateral slippage from October 7, 1965 to January 9, 1966. The average rate of movement would amount to about 0.21 inches per year. Variations in the measured displacement show no significant correlation with the present occurrence of small local earthquakes. A physical model of the observed fault slippage is outlined, based on the strain-release-by-rupture theory for the origin of shallow earthquakes. The model predicts that strain in the crystalline basement along the fault zone may be accumulating.

Movements and associated observations of bait-attracted White Sharks, Carcharodon carcharias: A preliminary report

1992 ◽  
Vol 43 (1) ◽  
pp. 13 ◽  
Author(s):  
WR Strong ◽  
RC Murphy ◽  
BD Bruce ◽  
DR Nelson
Keyword(s):  
Preliminary Report ◽  
Average Rate ◽  
South Australia ◽  
Movement Patterns ◽  
Population Parameters ◽  
Time Intervals ◽  
Horizontal Movement ◽  
Carcharodon Carcharias ◽  
Rate Of Movement

Basic population parameters and behaviours of great white sharks, Carcharodon carcharias, were studied during four expeditions to Spencer Gulf, South Australia. In all, 58 white sharks were observed, ranging in length from about 2.2 to 5.5 m TL (X= 3.7 m TL � 0.7 s.d.); of these sharks, 32 were subsequently tagged. Many sharks were observed repeatedly, the most frequently resighted individual being seen on 22 days over a 197-day period spanning two expeditions. Sharks in the study area were segregated by sex but not by size. Females were most abundant at 'inshore' islands, whereas males occurred mainly at 'offshore' islands. Further, there were no marked differences in abundance between summer and winter. Nine ultrasonic trackings, lasting a maximum of 27.5 h, revealed three general horizontal movement patterns: downstream circling, island patrolling, and inter-island cruising. Average rate of movement was 3.2 km h-1 (n = 145 time intervals of 15 min each). Sharks generally remained near the surface or along the bottom (about 20 m), spending relatively little time in midwater. Daytime swimming depths were significantly shallower than those at night.

Post 3.9 Ma fault activity within the West Antarctic rift system: onshore evidence from Gandalf Ridge, Mount Morning eruptive centre, southern Victoria Land, Antarctica

2010 ◽  
Vol 22 (5) ◽  
pp. 513-521 ◽  
Author(s):  
Adam P. Martin ◽  
Alan F. Cooper
Keyword(s):  
Ross Sea ◽  
Average Rate ◽  
Rift System ◽  
The West ◽  
West Antarctic ◽  
Eruptive Centre ◽  
Victoria Land ◽  
West Antarctic Rift System ◽  
West Antarctic Rift ◽  
Rate Of Movement

AbstractA hawaiite dyke dated at 3.88 ± 0.05 Ma from the Mount Morning eruptive centre intrudes a diamictite deposit at Gandalf Ridge in the southern Ross Sea. The dyke has been dextrally offset up to 6 m horizontally by faults interpreted as the onshore continuation of the West Antarctic rift system (WARS) fault array. Felsic dykes emplaced during the Miocene are also present at Gandalf Ridge. The offset of the Miocene dykes is equivalent to the offset on the hawaiite dyke, suggesting that at this locality movement on faults within WARS has been restricted to a period more recent than c. 3.88 Ma. Over this period the minimum average rate of movement on these faults within WARS is 0.0015 mm yr-1.

Random isn't real: How the patchy distribution of ecological rewards may generate “incentive hope”

2019 ◽  
Vol 42 ◽  
Author(s):  
Laurel Symes ◽  
Thalia Wheatley
Keyword(s):  
Natural Environment ◽  
Random Distribution ◽  
Spatiotemporal Distribution ◽  
Patchy Distribution ◽  
Distribution Of Resources

AbstractAnselme & Güntürkün generate exciting new insights by integrating two disparate fields to explain why uncertain rewards produce strong motivational effects. Their conclusions are developed in a framework that assumes a random distribution of resources, uncommon in the natural environment. We argue that, by considering a realistically clumped spatiotemporal distribution of resources, their conclusions will be stronger and more complete.

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