Spatial scale and sampling resolution affect measures of gap disturbance in a lowland tropical forest: implications for understanding forest regeneration and carbon storage

Treefall gaps play an important role in tropical forest dynamics and in determining above-ground biomass (AGB). However, our understanding of gap disturbance regimes is largely based either on surveys of forest plots that are small relative to spatial variation in gap disturbance, or on satellite imagery, which cannot accurately detect small gaps. We used high-resolution light detection and ranging data from a 1500 ha forest in Panama to: (i) determine how gap disturbance parameters are influenced by study area size, and the criteria used to define gaps; and (ii) to evaluate how accurately previous ground-based canopy height sampling can determine the size and location of gaps. We found that plot-scale disturbance parameters frequently differed significantly from those measured at the landscape-level, and that canopy height thresholds used to define gaps strongly influenced the gap-size distribution, an important metric influencing AGB. Furthermore, simulated ground surveys of canopy height frequently misrepresented the true location of gaps, which may affect conclusions about how relatively small canopy gaps affect successional processes and contribute to the maintenance of diversity. Across site comparisons need to consider how gap definition, scale and spatial resolution affect characterizations of gap disturbance, and its inferred importance for carbon storage and community composition.     

An alternative strategy for maintenance of eusociality after nest destruction: new nest construction in a primitively eusocial wasp

Although nests are central to colonial life in social insects, nests are sometimes damaged by predators or natural disasters. After nest destruction, individuals usually construct new nests. In this case, a sophisticated mechanism like the scent trail pheromone used in large insect colonies that recruit individuals to new nest sites would be important for the maintenance of eusociality. In independent-founding Polistes wasps, it is well known that queens enforce workers physiologically on the natal nests even if evidence of trail pheromone use has not been exhibited. We investigated the effect of the queen on an alternative strategy for the maintenance of eusociality by first females after nest destruction in the primitively eusocial wasp Polistes chinensis. We predicted that the first females in queen-absent colonies have various behavioral options after nest destruction. Even if the females construct new nests cooperatively with other individuals, the new nest construction should be conducted more smoothly in queen-present colonies because the queens regulate the behavior of wasps. We made wasps construct new nests by removing the entire brood from existing nests. The presence of the queen did not cause variation in the alternative strategy of the first females, as the first females (workers) usually constructed new nests cooperatively irrespective of the queen-presence. Thus, the workers in the queenpresent colonies affiliated to the new nest construction more smoothly and constructed new nests more efficiently than workers in the queen-absent colonies. Our results suggest that the presence of the queen is important for maintaining eusociality in primitively eusocial wasps after nest destruction. Received 8 February 2005; revised 5 October 2005; accepted 17 October 2005.     

Symbiotic nesting of birds with formidable animals: a review with applications to biodiversity conservation

Increased predation and parasitism of bird nests has become a major problem in many biological communities altered by human activities, often causing declines in bird populations. To help solve this threat to biodiversity, I propose restoring the abundance of symbiotic nest-protecting animals in habitats where birds face an increased risk from predators and parasites, so that birds there can increase their chances of reproductive success by nesting close to these protectors. The re-establishment of such protective nesting associations to increase avian reproductive success differs from other proposed solutions to this problem in that it involves point defense of bird nests themselves. Rather than diminishing the number of nest predators and brood parasites in the whole habitat or community, as proposed with other approaches, the presence, activity and success of these enemies are reduced only within the microhabitat defended by the protector. The animal protecting the nest need not be larger in size than the predators or brood parasites, and is often many times smaller. In addition, it need not be from a higher trophic position, and in many cases comes from the same or a lower trophic level. Research suggests that an informed and careful use of nest protecting animals by wildlife managers can help reverse or prevent the decline of many bird populations, especially when used in combination with other approaches such as restoration of top predator populations and habitats. Although wildlife biologists have long recognized the important role that plants play in concealing and protecting bird nests from enemies, and regularly recommend manipulation of vegetation to enhance nest survival, they have generally ignored the important role that formidable animals play in protecting bird nests, and failed to incorporate animal protectors into management strategies. Because of this neglect, a host of new studies and experiments are urgently needed to provide managers with the critical information needed to use protective nesting associations effectively in integrated strategies to preserve avian biodiversity.     

Host-parasite kinship in a female-philopatric bird population: evidence from relatedness trend analysis

Conspecific brood parasitism (CBP), an alternative reproductive tactic where some females lay eggs in the nests of other females of the same species, occurs in many animals with egg care. It is particularly common in waterfowl, for reasons that are debated. Many waterfowl females nest near their birthplace, making it likely that some local females are relatives. We analyse brood parasitism in a Hudson Bay population of common eiders, testing predictions from two alternative hypotheses on the role of relatedness in CBP. Some models predict host-parasite relatedness, others predict that parasites avoid close relatives as hosts. To distinguish between the alternatives, we use a novel approach, where the relatedness of host-parasite pairs is tested against the spatial population trend in pairwise relatedness. We estimate parasitism, nest take-over and relatedness with protein fingerprinting and bandsharing analysis of egg albumen, nondestructively sampled from each new egg in the nest throughout the laying period. The results refute the hypothesis that parasites avoid laying eggs in the nests of related hosts, and corroborate the alternative of host-parasite relatedness. With an estimated r of 0.12-0.14, females laying eggs in the same nest are on average closer kin than nesting neighbour females. Absence of a population trend in female pairwise relatedness vs. distance implies that host-parasite relatedness is not only an effect of strong natal philopatry: some additional form of kin bias is also involved.     

Food, vigilance, and sperm: the role of male direct benefits in the evolution of female preference in a polygamous bird

The adaptive significance of female selection of copulationpartners remains unresolved, particularly in polygamous specieswhere males do not provide paternal care. In these species thepossibility that direct benefits other than paternal care mayplay an important role in the evolution of female choice hasreceived little attention. I tested whether direct benefitsare associated with female choice in the polygamous feral fowl,Gallus g. domesticus, where females prefer socially dominantcopulation partners and males do not care for the young butdo provide females with three commodities: food, vigilance,and sperm. I used a combination of empirical and experimentaldata to show that male propensity to offer food and vigilance,but not sperm, was positively associated with male social status,suggesting that the provision of these resources may be costlyand condition dependent in males. Copulation success was correlatedwith male status but not with the number of feedings a femalereceived from a male, indicating that a female preferred dominantpartners that in general provided any female with more food,rather than partners that provided only her with more food,consistent with the idea that females may use male resourceprovisioning as a proximate mechanism to assess male condition.Together, these results indicate that male resources provisioningis (1) tightly linked to male social status, (2) a potentialindicator of male condition and possibly genetic quality, and(3) a potential criterion for females to select dominant partners,thus playing an important role in the evolution of partner choiceeven in polygamous species lacking paternal care.