Persistence Of Animal Populations Research Articles

Heatwaves inflict reproductive but not survival costs to male insects.

Climate change is having a dramatic effect on the environment, with rising global temperatures and more frequent extreme climatic events, such as heatwaves, that can hamper organisms' biological functions. Although it is clear that sudden and extreme temperatures can damage reproductive processes, there is limited understanding of the effects of heatwaves on male mating behaviour and reproductive success. We tested for the effects of heat stress induced by ecologically relevant heatwaves (33°C and 39°C for five consecutive days) on the mating behaviour, reproductive success, body mass and survival of male field crickets Gryllus bimaculatus, paired with untreated females. We predicted life-history and reproductive costs would increase with increasing heatwave intensity. Consistent with our expectations, males exposed to the highest heatwave temperature produced the fewest offspring, while having to increase courtship effort to successfully mate. Males also gained relatively more weight following heatwave exposure. Given that we found no difference in lifetime survival, our results suggest a potential trade-off in resource allocation between somatic maintenance and reproductive investment. Taken together, our findings indicate that sublethal effects of heatwaves could reduce the growth and persistence of animal populations by negatively impacting reproductive rates. These findings highlight the need for considering thermal ecologies, life history and behaviour to better understand the consequences of extreme climatic events on individuals and populations.

Development of urban behaviour is associated with time since urbanization in a reed-nesting waterbird

Behavioural adaptations are recognized as crucial determinants for successful establishment and persistence of animal populations in a novel urban environment. Here, we examined mechanisms responsible for the development of urban behavioural type in a common waterbird, the Eurasian coot Fulica atra. We compared the behaviour of coots from a rural population and two urban populations that differed in the timing of colonization event (1960s vs. 2000s). We found that some behavioural characters associated with urban life (aggression during nest defence and boldness towards humans during foraging) were more strongly expressed in the older urban population when compared with the recently established urban population. By contrast, coots from the two urban populations showed a similar likelihood of exploiting human-derived food resources, as well as they showed similar levels of physiological stress. Urban coots were generally more aggressive, bolder, and less stressed than their rural conspecifics. Large behavioural and physiological divergence of coots from the recently established urban population and their rural conspecifics suggested that phenotypic plasticity and phenotype sorting may play a key role in the initial stages of urban colonization. On the other hand, increasing expression of boldness and aggression with the time since urbanization may suggest the role of microevolutionary adaptation in response to novel selective forces associated with the urban environment. Our results indicate that a combination of different processes (phenotypic plasticity, phenotype sorting, and microevolution) can determine successful colonization of urban areas by the Eurasian coots, and possibly other bird species.

A simple epidemiological model for populations in the wild with Allee effects and disease-modified fitness.

The study of the dynamics of human infectious disease using deterministic models is typically carried out under the assumption that a critical mass of individuals is available and involved in the transmission process. However, in the study of animal disease dynamics where demographic considerations often play a significant role, this assumption must be weakened. Models of the dynamics of animal populations often naturally assume that the presence of a minimal number of individuals is essential to avoid extinction. In the ecological literature, this a priori requirement is commonly incorporated as an Allee effect. The focus here is on the study disease dynamics under the assumption that a critical mass of susceptible individuals is required to guarantee the population's survival. Specifically, the emphasis is on the study of the role of an Allee effect on a Susceptible-Infectious (SI) model where the possibility that susceptible and infected individuals reproduce, with the S-class the best fit. It is further assumed that infected individuals loose some of their ability to compete for resources, the cost imposed by the disease. These features are set in motion in as simple model as possible. They turn out to lead to a rich set of dynamical outcomes. This toy model supports the possibility of multi-stability (hysteresis), saddle node and Hopf bifurcations, and catastrophic events (disease-induced extinction). The analyses provide a full picture of the system under disease-free dynamics including disease-induced extinction and proceed to identify required conditions for disease persistence. We conclude that increases in (i) the maximum birth rate of a species, or (ii) in the relative reproductive ability of infected individuals, or (iii) in the competitive ability of a infected individuals at low density levels, or in (iv) the per-capita death rate (including disease-induced) of infected individuals, can stabilize the system (resulting in disease persistence). We further conclude that increases in (a) the Allee effect threshold, or (b) in disease transmission rates, or in (c) the competitive ability of infected individuals at high density levels, can destabilize the system, possibly leading to the eventual collapse of the population. The results obtained from the analyses of this toy model highlight the significant role that factors like an Allee effect may play on the survival and persistence of animal populations. Scientists involved in biological conservation and pest management or interested in finding sustainability solutions, may find these results of this study compelling enough to suggest additional focused research on the role of disease in the regulation and persistence of animal populations. The risk faced by endangered species may turn out to be a lot higher than initially thought.

Relative importance of natural disturbances and habitat degradation on snail kite population dynamics

Natural disturbances and habitat degradation are major factors influencing the dynam- ics and persistence of many wildlife populations, yet few large-scale studies have explored the rela- tive influence of these factors on the dynamics and persistence of animal populations. We used long- term demographic data and matrix population models to examine the potential effects of habitat degradation and natural disturbances on the dynamics of the endangered snail kite Rostrhamus sociabilis in Florida, USA. We found that estimates of stochastic population growth rate were low (0.90). Population growth rate (λ) during the first half or our study period (1992 to 1998) was substan- tially greater than during the second half (1999 to 2005). These 2 periods were characterized by con- trasting hydrological conditions. Although λ was most sensitive to changes in adult survival, the analysis of life table response experiments revealed that a reduction in fertility of kites accounted for >80% of the observed decline in population growth rate. We examined the possibility that the reduc- tion in λ was caused by (1) habitat degradation due to management, (2) an increase in frequency of moderate drying events in recent years, and (3) both habitat degradation and an increase in fre- quency of moderate drying events. Our results suggest that both factors could potentially contribute to a large decrease in population growth rate. Our study highlights the importance of simultaneously considering short- and long-term effects of disturbances when modeling population dynamics. Indeed, focusing exclusively on one type of effect may be misleading to both our understanding of the ecological dynamics of the system and to management. The relevance of our results to management is heightened because the snail kite has been selected as a key performance measure of one of the most ambitious ecosystem restoration projects ever undertaken.

INDIVIDUALS–AREA RELATIONSHIPS: THE RELATIONSHIP BETWEEN ANIMAL POPULATION DENSITY AND AREA

We compiled studies that report data on the relationship between animal population density and patch or island area for 287 individual species and 21 faunas. We tested the assumption of the equilibrium theory of island biogeography that population densities are independent of area by performing a meta-analysis using the linear correlation coefficient,r, as a measure of the effect of area on population density. We fit meta-analyses that used a random-effects model to these data to test for the effects of taxa, habitat, latitude, spatial scale, and overall population density. We also fit meta-analyses that used a fixed- effect model to the same data to estimate the repeatability of measurements of the correlation between population density and area within species. Contrary to the equilibrium theory of island biogeography, our results indicate that, on average, animal population densities are positively correlated with area, which suggests that density compensation may be uncommon. This result was found for individual species, but not for faunas. We found taxonomic differences in the correlation between population density and area, with insects and birds having on average large or moderately large positive correlations, respectively, and mammals having correlations near zero. Observations within individual species showed considerable repeatability. The observed overall positive cor- relation between the population density of individual animal species and area is best ex- plained in the context of the resource concentration hypothesis. Our results imply that the regional abundance and persistence of animal populations may depend strongly on the presence and continued persistence of a few large patches of suitable habitat, rather than on a regional network of small and large habitat patches.

The potential geographical distribution of the Old World screw‐worm fly, Chrysomya bezziana

The potential geographical distribution and relative abundance of the Old World screw-worm fly, Chrysomya bezziana Villeneuve (Diptera: Calliphoridae) as determined by climate, was assessed using CLIMEX, a computer program for matching climates. CLIMEX describes the relative growth and persistence of animal populations in relation to climate. The observed global distribution of C.bezziana was compared with the potential distribution predicted by CLIMEX. The differences in the two distributions indicate the areas at risk of colonization, with particular reference to Australia and the Americas. According to the model, the potential area of permanent colonization in Australia extends south to the mid-coast of New South Wales. Comparison of areas suitable for permanent establishment with the potential summer distribution indicates that large additional areas, carrying most of the continent's livestock, could be colonized in the summer months. Seasonal population growth indices are presented for three ports in Australia at which screw-worm fly specimens have been collected by quarantine authorities. They indicate the relative risk associated with introductions at different places in different seasons and so provide valuable planning information for quarantine authorities. The CLIMEX predictions for C.bezziana in North America are shown to be similar to the recorded distribution limits of the New World screw-worm fly, Cochliomyia hominivorax (Coquerel). The fly could also colonize South America, as far south as southern Brazil and midway through Argentina.