scholarly journals Functional responses of a cosmopolitan invader demonstrate intraspecific variability in consumer-resource dynamics

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e5634 ◽  
Author(s):  
Brett R. Howard ◽  
Daniel Barrios-O’Neill ◽  
Mhairi E. Alexander ◽  
Jaimie T.A. Dick ◽  
Thomas W. Therriault ◽  
...  
Keyword(s):  
South Africa ◽  
Northern Ireland ◽  
Functional Response ◽  
Ecological Impacts ◽  
Green Crab ◽  
Response Analysis ◽  
Feeding Rates ◽  
Functional Responses ◽  
Resource Dynamics ◽  
Consumer Resource

Background Variability in the ecological impacts of invasive species across their geographical ranges may decrease the accuracy of risk assessments. Comparative functional response analysis can be used to estimate invasive consumer-resource dynamics, explain impact variability, and thus potentially inform impact predictions. The European green crab (Carcinus maenas) has been introduced on multiple continents beyond its native range, although its ecological impacts appear to vary among populations and regions. Our aim was to test whether consumer-resource dynamics under standardized conditions are similarly variable across the current geographic distribution of green crab, and to identify correlated morphological features. Methods Crabs were collected from multiple populations within both native (Northern Ireland) and invasive regions (South Africa and Canada). Their functional responses to local mussels (Mytilus spp.) were tested. Attack rates and handling times were compared among green crab populations within each region, and among regions (Pacific Canada, Atlantic Canada, South Africa, and Northern Ireland). The effect of predator and prey morphology on prey consumption was investigated. Results Across regions, green crabs consumed prey according to a Type II (hyperbolic) functional response curve. Attack rates (i.e., the rate at which a predator finds and attacks prey), handling times and maximum feeding rates differed among regions. There was a trend toward higher attack rates in invasive than in native populations. Green crabs from Canada had lower handling times and thus higher maximum feeding rates than those from South Africa and Northern Ireland. Canadian and Northern Ireland crabs had significantly larger claws than South African crabs. Claw size was a more important predictor of the proportion of mussels killed than prey shell strength. Discussion The differences in functional response between regions reflect observed impacts of green crabs in the wild. This suggests that an understanding of consumer–resource dynamics (e.g., the per capita measure of predation), derived from simple, standardized experiments, might yield useful predictions of invader impacts across geographical ranges.

scholarly journals Pushing the switch: functional responses and prey switching by invasive lionfish may mediate their ecological impact

2021 ◽  
Author(s):  
Monica McCard ◽  
Josie South ◽  
Ross N. Cuthbert ◽  
James W. E. Dickey ◽  
Nathan McCard ◽  
...  
Keyword(s):  
Functional Response ◽  
Prey Species ◽  
Effective Means ◽  
Ecological Impact ◽  
Artemia Salina ◽  
Ecological Impacts ◽  
Feeding Rates ◽  
Functional Responses ◽  
Prey Switching ◽  
Frequency Dependent

AbstractBiodiversity is declining on a global scale and the spread of invasive alien species (IAS) is a major driver, particularly through predatory impacts. Thus, effective means of assessing and predicting the consequences of IAS predation on native prey population stability remains a vital goal for conservation. Here, we applied two classic ecological concepts, consumer functional response (FR) and prey switching, to predict and understand the ecological impacts of juveniles of the lionfish (Pterois volitans), a notorious and widespread marine invader. Functional responses and prey switching propensities were quantified towards three representative prey species: Artemia salina, Palaemonetes varians, and Gammarus oceanicus. Lionfish exhibited potentially destabilising Type II FRs towards individual prey species, owing to high consumption rates at low prey densities, whilst FR magnitudes differed among prey species. Functional response attack rates (a) were highest, and handling times (h) lowest, towards A. salina, followed by P. varians and then G. oceanicus. Maximum feeding rates (1/h) and functional response ratios (FRR; a/h) also followed this impact gradient for the three prey species. Lionfish, however, displayed a potentially population stabilising prey switching propensity (i.e. frequency-dependent predation) when multiple prey species were presented simultaneously, where disproportionately less of rare prey, and more of abundant prey, were consumed. Whilst FR and FRR magnitudes indicate marked per capita lionfish predatory impacts towards prey species, a strong prey switching propensity may reduce in-field impacts by offering low density prey refuge in biodiverse communities. Our results thus corroborate field patterns documenting variable impacts of lionfish, with prey extirpations less likely in diverse communities owing to frequency-dependent predation.

scholarly journals Impacts of non-native fishes under a seasonal temperature gradient are forecasted using functional responses and abundances

NeoBiota ◽  
2019 ◽  
Vol 49 ◽  
pp. 57-75 ◽  
Author(s):  
Lubabalo Mofu ◽  
Ross N. Cuthbert ◽  
Tatenda Dalu ◽  
Darragh J. Woodford ◽  
Ryan J. Wasserman ◽  
...  
Keyword(s):  
Functional Response ◽  
Fish Species ◽  
Ecological Impacts ◽  
Seasonal Temperature ◽  
Relative Impact ◽  
Feeding Rates ◽  
Functional Responses ◽  
Mozambique Tilapia ◽  
Western Mosquitofish ◽  
Native Fishes

Developing predictive methods to forecast the impacts of existing and emerging invasive species is of critical importance to biodiversity conservation. However, invader impacts are context-dependent, making reliable and robust predictions challenging. In particular, it is unclear how temporal variabilities in relation to temperature regime shifts influence invader ecological impacts. In the present study, we quantify the functional responses of three coexisting freshwater fishes: the native freshwater River Goby Glossogobiuscallidus, and the non-native Mozambique Tilapia Oreochromismossambicus and Western Mosquitofish Gambusiaaffinis, under two temperature treatments using chironomid larvae as prey. This was used along with fish abundance data to determine temporal differences in ecological impacts of each fish species between seasons (i.e. at two corresponding temperatures). All three fish species exhibited potentially population-destabilizing Type II functional responses. Their maximum feeding rates were consistently higher in the warm temperature treatment, whereas attack rates tended to be reduced. Non-native Mozambique Tilapia had the highest maximum feeding rate under both temperature treatments (18 °C and 25 °C), followed by the non-native Western Mosquitofish and lastly the native River Goby, suggesting greater per capita impacts on native prey by non-native fishes. The predatory fish abundances differed significantly according to season, with native River Goby and non-native Mozambique Tilapia generally more abundant than non-native Western Mosquitofish. By multiplying functional response maximum feeding rates with abundances of each fish species across the seasonal gradient, the relative impact potential of non-native Mozambique Tilapia was consistently higher compared to that of native gobies. Western Mosquitofish impacts were less apparent, owing to their low abundances. We demonstrate how seasonal temperature fluctuations affect the relative impact capacities of introduced species and the utility of consumer functional response and the relative impact potential metric in impact forecasting.

scholarly journals A cascade of evolutionary change alters consumer-resource dynamics and ecosystem function

2012 ◽  
Vol 279 (1741) ◽  
pp. 3184-3192 ◽  
Author(s):  
Matthew R. Walsh ◽  
John P. DeLong ◽  
Torrance C. Hanley ◽  
David M. Post
Keyword(s):  
Life History ◽  
Ecosystem Function ◽  
Life History Evolution ◽  
Evolutionary Change ◽  
Ecological Impacts ◽  
Trophic Levels ◽  
Natural Setting ◽  
Resource Dynamics ◽  
History Evolution ◽  
Consumer Resource

It is becoming increasingly clear that intraspecific evolutionary divergence influences the properties of populations, communities and ecosystems. The different ecological impacts of phenotypes and genotypes may alter selection on many species and promote a cascade of ecological and evolutionary change throughout the food web. Theory predicts that evolutionary interactions across trophic levels may contribute to hypothesized feedbacks between ecology and evolution. However, the importance of ‘cascading evolutionary change’ in a natural setting is unknown. In lakes in Connecticut, USA, variation in migratory behaviour and feeding morphology of a fish predator, the alewife ( Alosa pseudoharengus ), drives life-history evolution in a species of zooplankton prey ( Daphnia ambigua ). Here we evaluated the reciprocal impacts of Daphnia evolution on ecological processes in laboratory mesocosms. We show that life-history evolution in Daphnia facilitates divergence in rates of population growth, which in turn significantly alters consumer-resource dynamics and ecosystem function. These experimental results parallel trends observed in lakes. Such results argue that a cascade of evolutionary change, which has occurred over contemporary timescales, alters community and ecosystem processes.

Functional responses of optimal consumers and the potential for regulation of resource populations

1995 ◽  
Vol 22 (1) ◽  
pp. 101 ◽  
Author(s):  
OJ Schmitz
Keyword(s):  
Functional Response ◽  
Optimal Foraging Theory ◽  
Optimal Choice ◽  
Adaptive Behaviour ◽  
Positive Density ◽  
Functional Responses ◽  
Density Dependent ◽  
Time Period ◽  
Resource Interactions ◽  
Resource Dynamics

A central issue in studies of consumer-resource interactions is whether consumers regulate resource dynamics. One condition for regulation is that consumption rate of a resource increases positively with increasing resource density, that is, that the consumer's functional response must be positively density dependent. Many mammalian consumers exhibit density-independent or inversely density-dependent functional responses, suggesting that regulation will not occur. However, most studies measure functional responses for a single consumer and resource species in specific feeding trials. Many real-world consumers use more than one resource and resource choices depend on the distribution and nutritional quality of resources as well as abundances. Foragers also actively choose resources in ways that match predictions of optimal foraging theory, that is, they exhibit adaptive behaviour. This paper explores the variety of functional responses of adaptive consumers that arises from optimal choice of resources in a simple, singleconsumer- two-resource system to determine the potential for consumer regulation of resource populations. Optimal consumer behaviour can generate four types of functional responses: (1) density independent, (2) increasing, inverse density dependent, (3) increasing, positively density dependent, and (4) decreasing. A positive density-dependent functional response arises in 3 of 22 possible cases. Moreover, consumers may not exhibit the same functional response to all resources included in the diet, that is, they exhibit mixed responses to resource densities. This suggests that studies that examine the potential for consumer regulation of resources must go beyond the traditional focus (interactions between a consumer and the most dominant or abundant prey) and consider the variety of resource species selected by a consumer in a specified time period.

scholarly journals Existing and emerging high impact invasive species are characterized by higher functional responses than natives

2014 ◽  
Vol 10 (2) ◽  
pp. 20130946 ◽  
Author(s):  
Mhairi E. Alexander ◽  
Jaimie T. A. Dick ◽  
Olaf L. F. Weyl ◽  
Tamara B. Robinson ◽  
David M. Richardson
Keyword(s):  
Invasive Species ◽  
Micropterus Salmoides ◽  
Clarias Gariepinus ◽  
Research Priorities ◽  
Ecological Impacts ◽  
Feeding Rates ◽  
Functional Responses ◽  
Native Communities ◽  
Prey Handling ◽  
Invader Impact

Predicting ecological impacts of invasive species and identifying potentially damaging future invaders are research priorities. Since damage by invaders is characterized by their depletion of resources, comparisons of the ‘functional response’ (FR; resource uptake rate as a function of resource density) of invaders and natives might predict invader impact. We tested this by comparing FRs of the ecologically damaging ‘world's worst’ invasive fish, the largemouth bass ( Micropterus salmoides ), with a native equivalent, the Cape kurper ( Sandelia capensis ), and an emerging invader, the sharptooth catfish ( Clarias gariepinus ), with the native river goby ( Glossogobius callidus ), in South Africa, a global invasion hotspot . Using tadpoles ( Hyperolius marmoratus ) as prey, we found that the invaders consumed significantly more than natives. Attack rates at low prey densities within invader/native comparisons reflected similarities in predatory strategies; however, both invasive species displayed significantly higher Type II FRs than the native comparators. This was driven by significantly lower prey handling times by invaders, resulting in significantly higher maximum feeding rates. The higher FRs of these invaders are thus congruent with, and can predict, their impacts on native communities. Comparative FRs may be a rapid and reliable method for predicting ecological impacts of emerging and future invasive species.

scholarly journals Warming mediates intraspecific multiple predator effects from an invasive crustacean

2021 ◽  
Vol 168 (3) ◽  
Author(s):  
Ross N. Cuthbert ◽  
Ryan J. Wasserman ◽  
Tatenda Dalu ◽  
Elizabeta Briski
Keyword(s):  
Alien Species ◽  
Trophic Interactions ◽  
Invasive Alien Species ◽  
Ecological Impacts ◽  
Feeding Rates ◽  
Functional Responses ◽  
Multiple Predator Effects ◽  
Predator Interactions ◽  
The Impact ◽  
Predator Effects

AbstractInvasive alien species impacts might be mediated by environmental factors such as climatic warming. For invasive predators, multiple predator interactions could also exacerbate or dampen ecological impacts. These effects may be especially pronounced in highly diverse coastal ecosystems that are prone to profound and rapid regime shifts. We examine emergent effects of warming on the strength of intraspecific multiple predator effects from a highly successful invasive gammarid Gammarus tigrinus, using a functional response approach towards larval chironomids (feeding rates under different prey densities). Single predator maximum feeding rates were three-times higher at 24 °C compared to 18 °C overall, with potentially prey destabilising type II functional responses exhibited. However, pairs of gammarids exhibited intraspecific multiple predator effects that were in turn mediated by temperature regime, whereby synergisms were found at the lower temperature (i.e. positive non-trophic interactions) and antagonisms detected at the higher temperature (i.e. negative non-trophic interactions) under high prey densities. Accordingly, warming scenarios may worsen the impact of this invasive alien species, yet implications of temperature change are dependent on predator–predator interactions. Emergent effects between abiotic and biotic factors should be considered in ecological impact predictions across habitat types for invasive alien species.

scholarly journals The Stochastic Nature of Functional Responses

Entropy ◽  
2021 ◽  
Vol 23 (5) ◽  
pp. 575
Author(s):  
Gian Marco Palamara ◽  
José A. Capitán ◽  
David Alonso
Keyword(s):  
Stochastic Systems ◽  
Empirical Studies ◽  
Spatial Dynamics ◽  
Stochastic Approach ◽  
Linear Functions ◽  
Functional Responses ◽  
Ecological Processes ◽  
Feeding Experiments ◽  
Resource Dynamics ◽  
Consumer Resource

Functional responses are non-linear functions commonly used to describe the variation in the rate of consumption of resources by a consumer. They have been widely used in both theoretical and empirical studies, but a comprehensive understanding of their parameters at different levels of description remains elusive. Here, by depicting consumers and resources as stochastic systems of interacting particles, we present a minimal set of reactions for consumer resource dynamics. We rigorously derived the corresponding system of ODEs, from which we obtained via asymptotic expansions classical 2D consumer-resource dynamics, characterized by different functional responses. We also derived functional responses by focusing on the subset of reactions describing only the feeding process. This involves fixing the total number of consumers and resources, which we call chemostatic conditions. By comparing these two ways of deriving functional responses, we showed that classical functional response parameters in effective 2D consumer-resource dynamics differ from the same parameters obtained by measuring (or deriving) functional responses for typical feeding experiments under chemostatic conditions, which points to potential errors in interpreting empirical data. We finally discuss possible generalizations of our models to systems with multiple consumers and more complex population structures, including spatial dynamics. Our stochastic approach builds on fundamental ecological processes and has natural connections to basic ecological theory.

scholarly journals Nonlinear functional responses and ecological pleiotropy alter the strength of disruptive selection in consumers

2018 ◽  
Author(s):  
Kyle E. Coblentz
Keyword(s):  
Functional Response ◽  
Intraspecific Competition ◽  
Ecological Effects ◽  
Disruptive Selection ◽  
Feeding Rates ◽  
Functional Responses ◽  
Resource Model ◽  
Ecological Opportunity ◽  
Nonlinear Functional ◽  
Consumer Dependence

AbstractMuch of the theory on disruptive selection has focused on selection in generalist consumers caused by ecological opportunity through the availability of alternative resources and intraspecific competition for those resources. This theory, however, makes several ecologically unrealistic assumptions. First, this theory assumes that consumers have a linear, resource-dependent functional response, ignoring well-documented effects of resource handling times and consumer dependence. Second, this theory assumes that the trait under selection only influences the percapita attack rates of the consumer, ignoring other effects of the trait that may influence feeding rates and hence fitness. Here, I develop a one consumer-two resource model to investigate how nonlinear functional responses and ecological pleiotropy (traits that have multiple simultaneous ecological effects) influence the strength of disruptive selection. I find that handling times and interference among consumers are capable of altering disruptive selection by changing feeding rates differentially across consumer phenotypes. In particular, handling times cause a decrease in the strength of disruptive selection while the effects of interference depend on the mechanism through which interference occurs. The effects of handling times and interference, however, are dependent on whether and how ecological pleiotropy causes correlations between handling times or interference rates and attack rates. Overall, my results suggest that features defining the functional responses of consumers and the relationships among those features determine the likelihood and strength of disruptive selection. In particular, disruptive selection should be strongest in generalist populations composed of individual diet specialists who experience lower handling times and interference rates on the resources for which their attack rates are highest.

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