Advancing impact prediction and hypothesis testing in invasion ecology using a comparative functional response approach

Invasion ecology urgently requires predictive methodologies that can forecast the ecological impacts of existing, emerging and potential invasive species. We argue that many ecologically damaging invaders are characterised by their more efficient use of resources. Consequently, comparison of the classical ‘functional response’ (relationship between resource use and availability) between invasive and trophically analogous native species may allow prediction of invader ecological impact. We review the utility of species trait comparisons and the history and context of the use of functional responses in invasion ecology, then present our framework for the use of comparative functional responses. We show that functional response analyses, by describing the resource use of species over a range of resource availabilities, avoids many pitfalls of ‘snapshot’ assessments of resource use. Our framework demonstrates how comparisons of invader and native functional responses, within and between Type II and III functional responses, allow testing of the likely population-level outcomes of invasions for affected species. Furthermore, we describe how recent studies support the predictive capacity of this method; for example, the invasive ‘bloody red shrimp’ Hemimysis anomala shows higher Type II functional responses than native mysids and this corroborates, and could have predicted, actual invader impacts in the field. The comparative functional response method can also be used to examine differences in the impact of two or more invaders, two or more populations of the same invader, and the abiotic (e.g. temperature) and biotic (e.g. parasitism) context-dependencies of invader impacts. Our framework may also address the previous lack of rigour in testing major hypotheses in invasion ecology, such as the ‘enemy release’ and ‘biotic resistance’ hypotheses, as our approach explicitly considers demographic consequences for impacted resources, such as native and invasive prey species. We also identify potential challenges in the application of comparative functional responses in invasion ecology. These include incorporation of numerical responses, multiple predator effects and trait-mediated indirect interactions, replacement versus non-replacement study designs and the inclusion of functional responses in risk assessment frameworks. In future, the generation of sufficient case studies for a meta-analysis could test the overall hypothesis that comparative functional responses can indeed predict invasive species impacts.

Functional characterization of alpha-adrenoceptors mediating pupillary dilation in rats

Previously, we reported that the alpha(1A)-adrenoceptor, but not the alpha(1D)-adrenoceptor, mediates pupillary dilation elicited by sympathetic nerve stimulation in rats. This study was undertaken to further characterize the alpha-adrenoceptor subtypes mediating pupillary dilation in response to both neural and agonist activation. Pupillary dilator response curves were generated by intravenous injection of norepinephrine in pentobarbital-anesthetized rats. Involvement of alpha(1)-adrenoceptors was established as mydriatic responses were inhibited by systemic administration of nonselective alpha-adrenoceptor antagonists, phentolamine (0.3-3 mg/kg) and phenoxybenzamine (0.03-0.3 mg/kg), as well as by the selective alpha(1)-adrenoceptor antagonist, prazosin (0.3 mg/kg). The alpha(2)-adrenoceptor antagonist, rauwolscine (0.5 mg/kg), was without antagonistic effects. alpha(1A)-Adrenoceptor selective antagonists, 2-([2,6-dimethoxyphenoxyethyl]aminomethyl)-1,4-benzodioxane (WB-4101; 0.1-1 mg/kg) and 5-methylurapidil (0.1-1 mg/kg), the alpha(1B)-adrenoceptor selective antagonist, 4-amino-2-[4-[1-(benzyloxycarbonyl)-2(S)- [[(1,1-dimethylethyl)amino]carbonyl]-piperazinyl]-6,7-dimethoxyquinazoline (L-765314; 0.3-1 mg/kg), as well as the alpha(1D)-adrenoceptor selective antagonist, 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY-7378; 1 mg/kg), were used to delineate the adrenoceptor subtypes involved. Mydriatic responses to norepinephrine were significantly antagonized by intravenous administration of both WB-4101 and 5-methylurapidil, but neither by L-765314 nor by BMY-7378. L-765314 (0.3-3 mg/kg, i.v.) was also ineffective in inhibiting the mydriasis evoked by cervical sympathetic nerve stimulation. These results suggest that alpha(1B)-adrenoceptors do not mediate sympathetic mydriasis in rats, and that the alpha(1A)-adrenoceptor is the exclusive subtype mediating mydriatic responses in this species.

Taxonomic and functional diversity of farmland bird communities across Europe:Effects of biogeography and agricultural intensification

In eight European study sites (in Spain, Ireland, Netherlands, Germany, Poland, Estonia and Sweden), abundance of breeding farmland bird territories was obtained from 500 × 500 m survey plots (30 per area, N = 240) using the mapping method. Two analyses were performed: (I) a Canonical Correspondence Analysis of species abundance in relation to geographical location and variables measuring agricultural intensification at field and farm level to identify significant intensification variables and to estimate the fractions of total variance in bird abundance explained by geography and agricultural intensification; (II) several taxonomic and functional community indices were built and analysed using GLM in relation to the intensification variables found significant in the CCA. The geographical location of study sites alone explains nearly one fifth (19. 5%) of total variation in species abundance. The fraction of variance explained by agricultural intensification alone is much smaller (4. 3%), although significant. The intersection explains nearly two fifths (37. 8%) of variance in species abundance. Community indices are negatively affected by correlates of intensification like farm size and yield, whereas correlates of habitat availability and quality have positive effects on taxonomic and functional diversity of assemblages. Most of the purely geographical variation in farmland bird assemblage composition is associated to Mediterranean steppe species, reflecting the bio-geographical singularity of that assemblage and reinforcing the need to preserve this community. Taxonomic and functional diversity of farmland bird communities are negatively affected by agricultural intensification and positively affected by increasing farmland habitat availability and quality. © 2011 Springer Science+Business Media B.V.

A generalized functional response for predators that switch between multiple prey species

We develop a theory for the food intake of a predator that can switch between multiple prey species. The theory addresses empirical observations of prey switching and is based on the behavioural assumption that a predator tends to continue feeding on prey that are similar to the prey it has consumed last, in terms of, e.g., their morphology, defences, location, habitat choice, or behaviour. From a predator's dietary history and the assumed similarity relationship among prey species, we derive a general closed-form multi-species functional response for describing predators switching between multiple prey species. Our theory includes the Holling type II functional response as a special case and makes consistent predictions when populations of equivalent prey are aggregated or split. An analysis of the derived functional response enables us to highlight the following five main findings. (1) Prey switching leads to an approximate power-law relationship between ratios of prey abundance and prey intake, consistent with experimental data. (2) In agreement with empirical observations, the theory predicts an upper limit of 2 for the exponent of such power laws. (3) Our theory predicts deviations from power-law switching at very low and very high prey-abundance ratios. (4) The theory can predict the diet composition of a predator feeding on multiple prey species from diet observations for predators feeding only on pairs of prey species. (5) Predators foraging on more prey species will show less pronounced prey switching than predators foraging on fewer prey species, thus providing a natural explanation for the known difficulties of observing prey switching in the field. (C) 2013 Elsevier Ltd. All rights reserved.

Strawberry as a functional food:an evidence-based review

Emerging research provides substantial evidence to classify strawberries as a functional food with several preventive and therapeutic health benefits. Strawberries, a rich source of phytochemicals (ellagic acid, anthocyanins, quercetin, and catechin) and vitamins (ascorbic acid and folic acid), have been highly ranked among dietary sources of polyphenols and antioxidant capacity. It should however be noted that these bioactive factors can be significantly affected by differences in strawberry cultivars, agricultural practices, storage, and processing methods: freezing versus dry heat has been associated with maximum retention of strawberry bioactives in several studies. Nutritional epidemiology shows inverse association between strawberry consumption and incidence of hypertension or serum C-reactive protein; controlled feeding studies have identified the ability of strawberries to attenuate high-fat diet induced postprandial oxidative stress and inflammation, or postprandial hyperglycemia, or hyperlipidemia in subjects with cardiovascular risk factors. Mechanistic studies have elucidated specific biochemical pathways that might confer these protective effects of strawberries: upregulation of endothelial nitric oxide synthase (eNOS) activity, downregulation of NF-kB activity and subsequent inflammation, or inhibitions of carbohydrate digestive enzymes. These health effects may be attributed to the synergistic effects of nutrients and phytochemicals in strawberries. Further studies are needed to define the optimal dose and duration of strawberry intake in affecting levels of biomarkers or pathways related to chronic diseases.

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

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.