RELATIVE STRENGTH OF TOP-DOWN, BOTTOM-UP, AND CONSUMER SPECIES RICHNESS EFFECTS ON POND ECOSYSTEMS

2005 ◽  
Vol 75 (4) ◽  
pp. 489-504 ◽  
Author(s):  
Jeremy M. Wojdak
Keyword(s):  
Species Richness ◽  
Relative Strength ◽  
Top Down ◽  
Bottom Up ◽  
Pond Ecosystems

scholarly journals State-dependent changes in olfactory cortical networks via cholinergic modulation

2018 ◽  
Author(s):  
Donald A. Wilson ◽  
Maxime Juventin ◽  
Maria Ilina ◽  
Alessandro Pizzo ◽  
Catia Teixeira
Keyword(s):  
Olfactory Bulb ◽  
Entorhinal Cortex ◽  
Synaptic Input ◽  
Piriform Cortex ◽  
Receptor Activation ◽  
Relative Strength ◽  
Top Down ◽  
Cortical Networks ◽  
Bottom Up ◽  
State Dependent

AbstractActivity in sensory cortical networks reflects both peripheral sensory input and intra‐ and inter-cortical network input. How sensory cortices balance these diverse inputs to provide relatively stable, accurate representations of the external world is not well understood. Furthermore, neuromodulation could alter the balance of these inputs in a state‐ and behavior-dependent manner. Here, we used optogenetic stimulation to directly assay the relative strength of bottom-up (olfactory bulb) and top-down (lateral entorhinal cortex) synaptic inputs to piriform cortex in freely moving rats. Optotrodes in the piriform cortex were used to test the relative strength of these two inputs, in separate animals, with extracellular, monosynaptic evoked potentials. The results suggest a rapid state-dependent shift in the balance of bottom-up and top-down inputs to PCX, with enhancement in the strength of lateral entorhinal cortex synaptic input and stability or depression of olfactory bulb synaptic input during slow-wave sleep compared to waking. The shift is in part due to a state-dependent change in cholinergic tone as assessed with fiber photometry of GCaMP6 fluorescence in basal forebrain ChAT+ neurons, and blockade of the state-dependent synaptic shift with cholinergic muscarinic receptor activation.

scholarly journals Does climate limit species richness by limiting individual species’ ranges?

2014 ◽  
Vol 281 (1776) ◽  
pp. 20132695 ◽  
Author(s):  
Véronique Boucher-Lalonde ◽  
Jeremy T. Kerr ◽  
David J. Currie
Keyword(s):  
Species Richness ◽  
Natural Experiment ◽  
Migratory Birds ◽  
Individual Species ◽  
Strongly Correlated ◽  
Top Down ◽  
Bottom Up ◽  
Species Ranges ◽  
Number Of Species ◽  
Richness Patterns

Broad-scale geographical variation in species richness is strongly correlated with climate, yet the mechanisms underlying this correlation are still unclear. We test two broad classes of hypotheses to explain this pattern. Bottom-up hypotheses propose that the environment determines individual species’ ranges. Ranges then sum up to yield species richness patterns. Top-down hypotheses propose that the environment limits the number of species that occur in a region, but not which ones. We test these two classes of hypotheses using a natural experiment: seasonal changes in environmental variables and seasonal range shifts of 625 migratory birds in the Americas. We show that richness seasonally tracks the environment. By contrast, individual species’ geographical distributions do not. Rather, species occupy different sets of environmental conditions in two seasons. Our results are inconsistent with extant bottom-up hypotheses. Instead, a top-down mechanism appears to constrain the number of species that can occur in a given region.

PREDATION RISK AFFECTS RELATIVE STRENGTH OF TOP-DOWN AND BOTTOM-UP IMPACTS ON INSECT HERBIVORES

Ecology ◽  
2003 ◽  
Vol 84 (4) ◽  
pp. 1032-1044 ◽  
Author(s):  
Robert F. Denno ◽  
Claudio Gratton ◽  
Hartmut Döbel ◽  
Deborah L. Finke
Keyword(s):  
Predation Risk ◽  
Relative Strength ◽  
Insect Herbivores ◽  
Top Down ◽  
Bottom Up

scholarly journals Does management of a top carnivore influence the response of mesopredators and prey to rainfall in arid ecosystems? Evidence for a Baseline Density theory

2021 ◽  
Author(s):  
Renee L. Brawata
Keyword(s):  
Primary Productivity ◽  
Relative Strength ◽  
Trophic Levels ◽  
Arid Ecosystems ◽  
Top Down ◽  
Down Regulation ◽  
Bottom Up ◽  
Rate Of Increase ◽  
Abundance And Diversity

ABSTRACT The removal of apex carnivores from ecosystems can impact the abundance and diversity of species in lower trophic levels. In arid ecosystems, where “bottom up” forces of primary productivity and resource availability strongly affect trophic interactions, the role of “top down” effects is still much debated. This study explored the potential role of an apex predator, the dingo, as a “top down” trophic regulator in Australian arid ecosystems under different levels of primary productivity and dingo management regimes. Consistent with the theory of top down regulation, strong relationships were found between dingo management, dingo activity and fox activity. Dingoes appeared to suppress fox activity where dingoes were uncontrolled or only opportunistically controlled. At sites where dingoes were absent or in low numbers, fox activity was higher, and this inverse relationship persisted regardless of rainfall. The activity of rabbits and small mammals was lower where dingoes were absent and fox activity was high, while the activity of macropods was higher in the absence of dingoes. Feral cat activity did not differ significantly between sites under different dingo management or between years. These results suggest that management of dingoes is a key determinant of fox activity and the activity of some prey under varying levels of productivity. Evidence from this research showed that while the strength of trophic regulation by dingoes may fluctuate, top down effects occurred both prior to and post significant rainfall events. Following this, top down regulation of fox populations during dry periods at sites where dingoes are retained may enable higher and more stable “baseline” densities of small vertebrates, from which a larger and more rapid rate of increase of these prey during the “boom” periods can occur. Understanding the relative strength and interactions of top down and bottom up forces in regulating populations, and under what ecological states the importance of each changes, is important for the long-term conservation of biodiversity in arid regions.

Bottom-up and top-down processes influence contemporary patterns of mammal species richness in Australia's monsoonal tropics

2020 ◽  
Vol 247 ◽  
pp. 108638 ◽  
Author(s):  
A.M. Stobo-Wilson ◽  
D. Stokeld ◽  
L.D. Einoder ◽  
H.F. Davies ◽  
A. Fisher ◽  
...  
Keyword(s):  
Species Richness ◽  
Top Down ◽  
Mammal Species ◽  
Bottom Up

scholarly journals Trophic interactions among vertebrate guilds and plants shape global patterns in species diversity

2018 ◽  
Vol 285 (1883) ◽  
pp. 20180949 ◽  
Author(s):  
Jian Zhang ◽  
Hong Qian ◽  
Marco Girardello ◽  
Vincent Pellissier ◽  
Scott E. Nielsen ◽  
...  
Keyword(s):  
Species Richness ◽  
Species Diversity ◽  
Trophic Interactions ◽  
Large Scale ◽  
Environmental Drivers ◽  
Top Down ◽  
Bottom Up ◽  
Diversity Patterns ◽  
Biodiversity Patterns ◽  
Global Patterns

Trophic interactions play critical roles in structuring biotic communities. Understanding variation in trophic interactions among systems provides important insights into biodiversity maintenance and conservation. However, the relative importance of bottom-up versus top-down trophic processes for broad-scale patterns in biodiversity is poorly understood. Here, we used global datasets on species richness of vascular plants, mammals and breeding birds to evaluate the role of trophic interactions in shaping large-scale diversity patterns. Specifically, we used non-recursive structural equation models to test for top-down and bottom-up forcing of global species diversity patterns among plants and trophic guilds of mammals and birds (carnivores, invertivores and herbivores), while accounting for extrinsic environmental drivers. The results show that trophic linkages emerged as being more important to explaining species richness than extrinsic environmental drivers. In particular, there were strong, positive top-down interactions between mammal herbivores and plants, and moderate to strong bottom-up and/or top-down interactions between herbivores/invertivores and carnivores. Estimated trophic interactions for separate biogeographical regions were consistent with global patterns. Our findings demonstrate that, after accounting for environmental drivers, large-scale species richness patterns in plant and vertebrate taxa consistently support trophic interactions playing a major role in shaping global patterns in biodiversity. Furthermore, these results suggest that top-down forces often play strong complementary roles relative to bottom-up drivers in structuring biodiversity patterns across trophic levels. These findings underscore the importance of integrating trophic forcing mechanisms into studies of biodiversity patterns.

Psychology and Culture: Top Down Versus Bottom Up?

PsycCRITIQUES ◽  
2005 ◽  
Vol 50 (19) ◽  
Author(s):  
Michael Cole
Keyword(s):  
Top Down ◽  
Bottom Up
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