Adela González-Megías

Escape from natural enemies during climate-driven range expansion: a case study

Abstract 1. A major, and largely unexplored, uncertainty in projecting the impact of climate change on biodiversity is the consequence of altered interspecific interactions, for example between parasitoids and their hosts. The present study investigated parasitism in the Brown Argus butterfly, Aricia agestis; a species that has expanded northward in Britain during the last 30  years in association with climate warming.

DIRECT AND INDIRECT EFFECTS OF CLIMATE AND HABITAT FACTORS ON BUTTERFLY DIVERSITY

Many factors, including climate, resource availability, and habitat diversity, have been proposed as determinants of global diversity, but the links among them have rarely been studied. Using structural equation modeling (SEM), we investigated direct and indirect effects of climate variables, host-plant richness, and habitat diversity on butterfly species richness across Britain, at 20-km grid resolution. These factors were all important determinants of butterfly diversity, but their relative contributions differed between habitat generalists and specialists, and whether the effects were direct or indirect. Climate variables had strong effects on habitat generalists, whereas host-plant richness and habitat diversity contributed relatively more for habitat specialists. Considering total effects (direct and indirect together), climate variables had the strongest link to butterfly species richness for all groups of species. The results suggest that different mechanistic hypotheses to explain species richness may be more appropriate for habitat generalists and specialists, with generalists hypothesized to show direct physiological limitations and specialists additionally being constrained by trophic interactions (climate affecting host-plant richness).

ASYMMETRICAL INTERACTIONS BETWEEN UNGULATES AND PHYTOPHAGOUS INSECTS: BEING DIFFERENT MATTERS

We conducted a 3-yr field experiment that manipulated the presence of ungulates (domestic sheep and Spanish ibex Capra pyrenaica, Bovidae) and the monophagous beetle Timarcha lugens (Chrysomelidae) to evaluate (1) the effects on beetle abundance and interaction with the woody crucifer Hormathophylla spinosa; (2) the reciprocal effect of this insect on the interaction between ungulates and the plant; (3) their impact on H. spinosa reproductive output; and (4) the abundance of an associated taxon, Ceutorhynchus sp. nov. (Curculionidae). Our experiment showed that ungulate exclusion increased Timarcha abundance, whereas Timarcha had no effect on ungulates. H. spinosa reproductive output increased threefold promptly when ungulates were excluded, although in the third year Timarcha began to have effects on shrub reproduction. Ungulates affected weevils both by exploitative competition and by incidental predation, with the total number of weevils emerging per shrub being more than fourfold higher in shrubs excl...

Effects of ungulates on epigeal arthropods in Sierra Nevada National Park (southeast Spain)

This paper examines the effect of ungulates on epigeal arthropod communities in two common plant communities of the high mountains of the Sierra Nevada (southeast Spain). We have compared the abundance, biomass, diversity and specific composition of arthropod communities in grazed and ungrazed plots experimentally excluded from ungulates. In general, we found that arthropods were more abundant and diverse in grazed than in ungrazed plots. However, the effect of ungulates depended on the variable considered (diversity versus abundance versus biomass). Moreover, ungulates also affected species composition. This means that without affecting diversity, ungulates can still have a strong effect on arthropod communities by changing species composition. Also, the relationship between ungulates and arthropods differed depending on the year of study and the sampling period. In conclusion, our study indicates that to extrapolate the results obtained for a group of insects, a habitat or a sampling period is not appropriate for the conservation of arthropod communities.

Long‐term effects of ungulates on phytophagous insects

Abstract 1. Most plants interact with a diverse suite of herbivores, allowing the opportunity for the existence of positive and negative interactions between highly dissimilar organisms. However, most studies on herbivorous interactions have been performed under the assumption that they occur mainly between similar species. Consequently, ecologists are still far from a full understanding of the ecological factors that determine insect population dynamics.

CONSEQUENCES OF SPATIAL AUTOCORRELATION FOR THE ANALYSIS OF METAPOPULATION DYNAMICS

The importance of spatial and temporal autocorrelation for the processes occurring at many different scales has been pointed out in the last few years. Although the role of spatial pattern in models on metapopulation dynamics has recently been recognized, there is a lack of empirical studies accounting for the consequences of considering auto- correlation in these processes. Here, we show that the conventional statistical methods used for determining the factors controlling species population dynamics (species density, sex ratio, and extinction events) can be strongly affected by spatial autocorrelation. Under these circumstances, the use of a spatially explicit model is highly recommended in order to demonstrate the real factor controlling species population dynamics. Moreover, presenting erroneous conclusions concerning the real factors governing species population dynamics could have far-reaching consequences in the management and conservation of many en- dangered species.

The phylogenetic roots of human lethal violence

The psychological, sociological and evolutionary roots of conspecific violence in humans are still debated, despite attracting the attention of intellectuals for over two millennia. Here we propose a conceptual approach towards understanding these roots based on the assumption that aggression in mammals, including humans, has a significant phylogenetic component. By compiling sources of mortality from a comprehensive sample of mammals, we assessed the percentage of deaths due to conspecifics and, using phylogenetic comparative tools, predicted this value for humans. The proportion of human deaths phylogenetically predicted to be caused by interpersonal violence stood at 2%. This value was similar to the one phylogenetically inferred for the evolutionary ancestor of primates and apes, indicating that a certain level of lethal violence arises owing to our position within the phylogeny of mammals. It was also similar to the percentage seen in prehistoric bands and tribes, indicating that we were as lethally violent then as common mammalian evolutionary history would predict. However, the level of lethal violence has changed through human history and can be associated with changes in the socio-political organization of human populations. Our study provides a detailed phylogenetic and historical context against which to compare levels of lethal violence observed throughout our history.

Consequences of removing a keystone herbivore for the abundance and diversity of arthropods associated with a cruciferous shrub

Abstract. 1. The effect of the removal of Timarcha lugens (Chrysomelidae), one of the main herbivores of Hormathophylla spinosa (Cruciferae), on the abundance of co‐occurring phytophagous insects, the abundance of non‐phytophagous arthropods (detritivores, predators, and parasitoids), and the structure and diversity of the entire arthropod community, was studied for 3 years (1999–2001).

Effects of brood parasitism on host reproductive success: evidence from larval interactions among dung beetles.

Abstract. This paper investigates the effect of brood parasitism in a dung beetle assemblage in an arid region of Spain. The study was conducted during the spring season (March–May 1994–1998) using mesh cylinders buried into the ground, filled with sand and with sheep dung on top. We quantified the proportion of nests containing larvae of parasitic beetles and their effect on host larvae survival. Experiments on the effect of parasitic larvae on host-larvae survival were conducted by placing scarab brood masses (raised from captive scarabs in the laboratory) in containers with and without aphodiid larvae. During the spring, dung desiccation is rapid, preventing aphodiids nesting in the dung, and forcing these species to adopt brood parasitism as a nesting strategy. Parasitic aphodiids were found in 12–47% of scarab nests of three species. The incidence of brood parasitization was positively related with the number of brood masses contained in the nests, being also higher in the most abundant species. Field data and experiments showed that brood parasites significantly reduced host larvae survival from 74.8% in non-parasitized nests to 8.8% in parasitized nests. Because different rates of nest parasitization and mortality were caused by parasites, brood parasitism had a differential effect on different host species. Thus, brood parasitism constitutes an important mortality factor reducing the reproductive success of the host species and potentially affecting the beetle abundance in the area.

Adult and Larval Plant Range and Preference in Timarcha lugens (Coleoptera: Chrysomelidae): Strict Monophagy on an Atypical Host

Abstract We investigated the host range and preference of the high-mountain species Timarcha lugens Rosenhauer, an insect species with highly mobile larvae, testing the degree of specialization and the correlation between larval and adult preference for host plant. All 720 larvae, 1,035 adult females and 994 adult males, censused in the field over 3 yr (1997–1999) and in 20 populations located along all the distribution area of the species were living on one single host plant, Hormathophylla spinosa Küpfer (Cruciferae). This differs from other Old World Timarcha, which are adapted to feed on Plantaginaceae and Rubiaceae. Laboratory experiments confirmed these observational results; all 130 beetles tested fed only on H. spinosa, and no beetle accepted any other plant species either in choice or nonchoice experiments. Larval and adult preference proved identical, both stages selecting only H. spinosa. We suggest that T. lugens has evolved the ability to attack an atypical host.