Environmental impacts and behavior
Gil Rosenthal and Salvador Contreras-Balderas, organizers
Behavior is a bellwether of the viability of animal populations. The most immediate and visible responses to a disturbance are usually behavioral. Environmental changes can also severely impair critical behaviors even if they have no detectable physiological or toxicological effect. Conversely, human-induced disturbances can serve as powerful, if unfortunate, experimental models in behavioral ecology. The proposed symposium addresses the impact of species introductions and habitat alteration on social structure, foraging behavior, mate choice, and communication. The symposium is particularly topical in light of the meetingÕs location in Oaxaca. Developing countries host a disproportionate share of the worldÕs threatened biodiversity. A major goal of this symposium is to increase awareness of the centrality of behavior to conservation. Behavioral methods can also provide an economically feasible research tool to scientists from the developing world. Finally, animal behavior has historically been underrepresented in Mexican biology. By linking behavior to the better-populated field of conservation biology, we hope to stimulate behavioral research in the Mexican scientific community.
Salvador Contreras-Balderas, Autonomous University of Nuevo León
Species introductions and behavior: a perspective from Mexican ichthyology
Exotic fish species, often introduced as a result of deliberate government policy, sometimes by unaware aquarists, or as escapes from farms, are a ubiquitous threat to the biology of freshwater ecosystems. Behavioral differences and behavioral interactions between invasive andindigenous species can increase the harmful impact of exotics. The continental waters of Mexico contain over 68 documented introduced species, some of which can be directly linked to the extirpation of local populations. Several examples are discussed in which behavior has played acritical role in ecological interactions between exotics and natives. The Central American cichlid Herichthys nigrofasciatum is established in the northern R’o P‡nuco basin of Hidalgo and Veracruz states. Direct competition for nest sites with indigenous species employing similarbiparental care strategies appears to be limiting recruitment of native cichlids. An apparent expansion of the diet of the Asian grass carp, Ctenopharyngodon idella, with respect to its diet within its native range, has led to the displacement of nearly all native species in parts of the R’oUsumacinta. Male introduced pupfish Cyprinodon variegatus have a mating advantage over endemic congeners in northeastern Mexico and the southwestern United States, leading to extinction of these endemics through hybridization. Populations of the Mexican golden trout, Oncorhyncus chrysogaster, have been displaced by introduced rainbow trout, Oncorhyncus mykiss. Due to the foraging and habitat-use strategies of the latter species, traditional indigenous fishing techniques are ineffective, forcing local indigenous people to use costlier contemporary fishing approaches. Often introduced species from highly saturated fish faunas into smaller fish communities, aggresively displace the natives, due to the more "rural" or naive behavioral adaptations of the locals. These examples illustrate the importance of behavior to the impact of introduced species, and serve to urge caution in the practice of deliberately introducing exotics.
Sharon Downes, Australian National University
Cascading behavioral responses to habitat degradation
Colonization of open vegetation by dense sprawling weeds causes major changes to the thermal environment experienced by ground-dwelling animals. In such microhabitats ectotherms are predicted to suffer decreased rates of growth due to restricted thermoregulatory opportunities. However, this may not be the case if animals can adjust body temperatures within optimal ranges by shifting basking behaviour. For example, animals can be exposed to full sunlight by climbing the stalks of weeds to reach the canopy. In turn, this change in behaviour can have implications for the expression of morphology, particularly limb length, due to phenotypic plasticity. We are examining cascading behavioural responses to habitat degradation using a common garden skink (Lampropholis delicata) and a prolific environmental weed (blue periwinkle, Vinca major) as a model experimental system. Periwinkle differs substantially from the displaced native vegetation by being more structurally complex and allowing less sunlight to reach the ground. Garden skinks are diurnal heliothermic lizards that depend on sunlight for growth and maintenance, and reproduce in the year following birth. Previous work demonstrates that this species exhibits plasticity in morphology when exposed to different thermal rearing environments. Using a replicated split-clutch design, we introduced newborn lizards into semi-natural landscapes manipulated to represent severe, moderate and no invasion by periwinkle. By recording the body sizes of hatchling lizards over the following year we determined the consequences of weed invasion for rates of growth and reproductive output. Simultaneously, we used an integrated set of observations and experiments to examine shifts in basking behaviour by lizards in different environments, and used microscopic imaging to obtain detailed measurements of morphology (including limb length).
John Eadie, University of California Davis
From landscapes to loci: disturbance, demography, behavior and the link to local population genetic structure.
Traditional conservation genetics has explored in detail the impacts of habitat loss and fragmentation on population genetic structure (reduced gene flow, loss of genetic diversity, increased inbreeding). Similarly, heightened interest in the behavior-conservation interface has produced a number of studies on the effects of environmental disturbance on mating systems, social systems and reproductive behavior, although the links to demography and population genetic structure are often implied rather than demonstrated. In contrast, efforts to link behavior and local population structure, from a conservation perspective, are in their infancy. To link landscapes to loci will require examination of the effects of an environmental disturbance not only on demography and behavior, but also on (1) changes in behavior brought about by alteration of population size or structure (e.g., density-dependence), (2) reciprocal influences of behavioral changes on demographic trajectories, (4) the consequences of these changes on the local population genetic structure, and (5) the influence of the local genetic structure on the fitness of behavioral phenotypes and population viability. I illustrate these ideas with our studies of cavity-nesting waterfowl where we know (1) the effect of habitat alteration on the frequency of female alternative behaviors (conspecific brood parasitism), (2) the impact of this behavior on population demography, (3) the reciprocal effect of population density on the success of the alternative behaviors (nest or parasitize), and (4) the link between the behavior and population genetic structure (primarily with respect to the level of kinship within and among local populations). In doing so, I examine how habitat alterations could have far reaching effects, not only on behavioral systems and demography, but on the local population genetic structure as well.
Francisco Garcia de León, Technological Institute of Ciudad Victoria
Environmental degradation and behavioral evolution: insights from a hybrid zone
Environmental disturbance can drive the evolution of behavior in several ways: by altering the selective regime, by creating genetic bottlenecks, and by altering gene flow among populations, subpopulations, or sympatric species. Two poeciliid fish species, the swordtails Xiphophorus malinche and X. birchmanni, hybridize in and around the R’o Calnali, Hidalgo, in the eastern Sierra Madre of Mexico. The two species are highly sexually dimorphic with divergent male sexual signals in the two species. The area was subject to massive fish kills associated with mining activity in the mid-1960s, reflected in low present-day mitochondrial haplotype diversity. In subsequent years, the hybrid zone has been subject to increasing impact from drought, agricultural use, human waste, fishing, domestic water use, and urbanization. Hybrids represent a range of recombinant sexual phenotypes. Hybridization may be facilitated by alteration of the chemical and visual environment. In repeated sampling over a five-year period, genotypes associated with X. birchmanni increased in frequency. This appears to be due in part to a mate-choice asymmetry whereby X. birchmanni females are more discriminating of conspecifics, and in part due to the suppression of migration from X. malinche source populations following installation of a sewage outflow. Male body size, a trait attractive to female swordtails, has shown a significant reduction downstream of the outflow. The distribution of male display traits thus appears to be the result of a combination of disturbance effects: a breakdown of species recognition caused by habitat degradation and/or a recent genetic bottleneck; disruption of migration by habitat fragmentation; and changes in selection on life-history traits correlated with body size.
Astrid Kodric-Brown, University of New Mexico
Mate choice, hybridization, and species introductions
Freshwater fishes, especially those in the southwestern North America and Mexico, have been heavily impacted by anthropogenic activities. Movement of fishes between water sources, such as accidental release of bait fish, or deliberate stocking of game fish, have contributed to hybridization and genetic introgression between closely related species. Through changes in patterns of mate choice and competition for mates, secondary contact between allopatric species may affect both the intensity and direction of intra- and intersexual selection. Studies of female preferences for conspecific and heterospecific males in sympatry and allopatry provide the opportunity to investigate the presence and strength of premating isolating mechanisms. Pupfishes (Cyprinodon) are particularly well suited for behavioral studies of mating preferences, because all stages of mate recognition systems are represented, from complete premating isolation (some Mexican pupfishes), to complete absence (Pecos pupfish). Studying female mating preferences and male-male competition in other freshwater fishes should provide insights into behavioral mechanisms that facilitate or retard hybridization between congeners.
Gil Rosenthal, Boston University
Coral reef extinction and behavior: a very long-term view of reef fish evolution
Massive coral bleaching and eutrophication both threaten coral reef environments. One of the important consequences of this process is a substantial change in the visual environment. Background characteristics in reef environments become homogenized as corals die, and eutrophication alters and narrows the distribution of ambient light. The last massive coral extinction we can trace occurred 2-3 million years ago with the closure of the Isthmus of Panama and the transition of the eastern Pacific from a coral reef environment, likely characterized by bright, clear water, to a productive, murky rocky reef environment. Comparisons of the visual conspicuousness and visual sensitivity of Caribbean fishes, as compared to their close relatives in the eastern Pacific, reveal that the eastern Pacific transition was accompanied by substantial shifts in both reef fish color and spectral sensitivity. Theoretical calculations of the conspicuousness of Caribbean fish in an eastern Pacific environment indicate that conspicuousness is minimized in the Caribbean fishesÕ native environment. These comparisons suggest that selection has favored divergence of visual communication systems in response to shifts in the visual environment. The rapid timescale of ongoing changes is likely to preclude a similar response to current disturbance.
Michael Singer, University of Texas
Ecological and evolutionary consequences of human-induced maladaptation of food choice in butterflies.
Human land management practices dramatically alter the selective environment for herbivorous insects. First, they alter the species composition of plant communities by removing and adding plant species. Second, they alter the relative quality of existing plant species from the perspective of herbivores. Both these processes have generated strong natural selection on herbivore food preferences, with consequent rapid evolution of host-choice behavior. Working with checkerspot butterflies in the Western USA, we have studied one example where a novel host has been added to the plant community, and one where the quality of existing plants has been changed. In the first case, a European weed was introduced to a site where 10% of the butterflies (Edith's checkerspot) would accept it readily for oviposition, but none preferred it. The novel host supported about ten times higher offspring fitness than the traditional host. Heritability of oviposition preference was estimated at 0.9, so rapid evolution of preference was predicted. This prediction has been fulfilled, and by 2002 96% of the population was using the introduced weed.
Our second example involves effects of clear-cutting in a forest, which created a patchwork of clearings embedded in a matrix of undisturbed habitat. This logging removed the traditional host of the butterflies, which was parasitic on trees. At the same time, the fertilization that followed logging and burning of trash rendered an abundant native annual plant suitable as a host by extending its life span sufficiently to accommodate the life cycle of the insect. There was strong natural selection to oviposit on this novel host in clearings, and strong selection against using it in undisturbed patches. Despite retaining a suite of behavioral adaptations to the traditional host, the insects colonized the novel host and achieved high densities on it for more than 12 years, during which the clearings acted as ecological sources and undisturbed patches as apparent sinks. However, evolution of behavioral adaptations to the novel host was slow, allowing environmental fluctuations to extirpate the butterflies from the cleared patches. The insects have now abandoned their novel host and returned to their traditional host. However, recent experiments show that that the highest fitness in the habitat would stem from use of the novel host, provided that the insects were behaviorally well-adapted to it. They have fallen off an adaptive peak.
Hans Slabbekoorn, Leiden University
Communication strategies in altered environments
The ongoing spread of urban areas, highways, and airports throughout the world makes anthropogenic noise almost omnipresent. Cars, planes, and all sorts of machinery create evolutionarily speaking a new selection pressure to wildlife that use acoustic signals. This selection experiment of unparalleled proportions may cause a rift between species that can adapt their signals and those that cannot and will eventually vanish. However, although several studies report a decline in species density and diversity associated with sprawling cities and highways, there is no evidence yet for a direct mechanistic role of sound pollution, nor is there much insight into how urban species do cope under the noisy circumstances. The great tit (Parus major) is a bird species originally only residing in forest free from anthropogenic noise, but it is now also thriving in noisy city centers and along busy highways. This species will serve as a case study on a Ôurban survivorÕ to gain insight into which species are likely most affected by noise conditions in human-altered environments.
Andy Suarez, University of Illinois
Behavioral mechanisms of success in biological invasions
A principal goal of invasion biology is to identify traits that allow species to successfully invade novel environments. Behavioral mechanisms may be important determinants of invasion success as recently demonstrated in a wide variety of taxa. I use ant invasions to illustrate how behavioral traits may facilitate a species' success at different stages of the invasion process. I also discuss how the study of animal invasions provides an underutilized opportunity for basic research in animal behavio.
Pamela Yeh, University of California San Diego
Behavioral adaptations to urbanization
Behavior and other forms of phenotypic plasticity enable individuals to dealwith novel situations. Urbanization has created a unique environment for birds. There are many behavioral changes that can occur when a population becomesestablished in urban areas, and these changes should increase an individual?sfitness, but this has rarely been investigated and quantified in naturalpopulations. I investigated three breeding behaviors in urban juncos that arerare or entirely absent in juncos breeding in natural habitats: breeding for upto five months per year (compared with ~ 2 months in the the native habitat);building nests off the ground, and re-using old nests. I demonstrate thatfirst, not all individuals within the urban population engage in thesebehaviors; second, all of these behavioral changes are under positive,directional selection; and third, the new behaviors have consequences forreproductive success but not adult survival. I suggest that novel habitats cancause changes in breeding behaviors that enhance fitness, but there may bephysiological, social or ecological constraints that keep some individuals fromengaging in the advantageous new behaviors.