Changes In Population Abundance Research Articles

The impact of data resolution on dynamic causal inference in multiscale ecological networks.

While it is commonly accepted that ecosystem dynamics are nonlinear, what is often not acknowledged is that nonlinearity implies scale-dependence. With the increasing availability of high-resolution ecological time series, there is a growing need to understand how scale and resolution in the data affect the construction and interpretation of causal networks-specifically, networks mapping how changes in one variable drive changes in others as part of a shared dynamic system ("dynamic causation"). We use Convergent Cross Mapping (CCM), a method specifically designed to measure dynamic causation, to study the effects of varying temporal and taxonomic/functional resolution in data when constructing ecological causal networks. As the system is viewed at different scales relationships will appear and disappear. The relationship between data resolution and interaction presence is not random: the temporal scale at which a relationship is uncovered identifies a biologically relevant scale that drives changes in population abundance. Further, causal relationships between taxonomic aggregates (low-resolution) are shown to be influenced by the number of interactions between their component species (high-resolution). Because no single level of resolution captures all the causal links in a system, a more complete understanding requires multiple levels when constructing causal networks.

Motion‐sensitive cameras track population abundance changes in a boreal mammal community in southwestern Yukon, Canada

AbstractMotion‐sensitive cameras are commonly used to monitor wildlife occupancy rates; however, few studies have assessed whether data from cameras are correlated with density estimates obtained from more traditional labor‐intensive methods such as those based on capture‐mark‐recapture. We used data from a boreal forest community to test whether camera data were correlated with densities estimated from independent monitoring methods. We placed 72 covert cameras in the forest around Lhù'ààn Mân' (Kluane Lake), Yukon, Canada, for 7 years and tracked changes in population densities by camera hit rates. We independently estimated population densities of snowshoe hares (Lepus americanus) and red squirrels (Tamiasciurus hudsonicus) using capture‐mark‐recapture via live trapping, and Canada lynx (Lynx canadensis), coyotes (Canis latrans), and moose (Alces americanus) by snow track transects. Density estimates obtained from conventional aerial surveys were also periodically available for moose. Except for red squirrels, camera hit rates were highly correlated with population density estimates obtained by traditional methods, including across a large range of estimated densities corresponding to cyclic population dynamics in several species. Accordingly, we infer that motion‐sensitive cameras could supplement or replace traditional methods for monitoring key species in boreal forest food webs. Using cameras to monitor population change has several advantages; they require less effort in the field, are non‐invasive compared to live‐trapping, include multiple species at the same time, and rely less on weather than either aerial surveys or snow track transects. Tracking changes across the vast boreal forest is becoming increasingly necessary because of climate and landscape change and our data validate the use of motion‐sensitive cameras to provide a useful quantitative method for state‐of‐the‐environment reporting.

Multiple lines of evidence highlight the dire straits of yellowfin tuna in the Indian Ocean.

Yellowfin tuna (Thunnus albacares) are highly valued pelagic fisheries target species. Regional fisheries management organizations (RFMOs) are the principal mechanism that manage yellowfin tuna fisheries. Determining changes in population abundances is crucial for effective conservation and management. We use multiple methods for monitoring biomass trends and evaluating the status of yellowfin tuna in each ocean basin and show how additional, multiple lines of evidence can enhance our understanding of the conservation and exploitation status of this species. Our analysis of regional biomass trajectories and Catch-MSY++ assessments corroborate the findings of the most recent RFMO stock assessments suggesting yellowfin tuna in the Indian Ocean are in critical condition, while the Eastern Pacific yellowfin tuna population shows the lowest levels of exploitation. These results are supported by fisheries-independent data from baited remote underwater video systems (BRUVS), showing that the Indian Ocean yellowfin tuna population is the least common, least abundant, and smallest across all oceans. Our findings support previous claims of systematic and widespread overfishing of yellowfin tuna in the Indian Ocean and thus confirm calls to reduce current fishing levels to ensure the long-term viability of the species.

Logistic-growth models measuring density feedback are sensitive to population declines, but not fluctuating carrying capacity.

Analysis of long-term trends in abundance of animal populations provides insights into population dynamics. Population growth rates are the emergent interplay of inter alia fertility, survival, and dispersal. However, the density feedbacks operating on some vital rates ("component feedback") can be decoupled from density feedbacks on population growth rates estimated using abundance time series ("ensemble feedback"). Many of the mechanisms responsible for this decoupling are poorly understood, thereby questioning the validity of using logistic-growth models versus vital rates to infer long-term population trends. To examine which conditions lead to decoupling, we simulated age-structured populations of long-lived vertebrates experiencing component density feedbacks on survival. We then quantified how imposed stochasticity in survival rates, density-independent mortality (catastrophes, harvest-like removal of individuals) and variation in carrying capacity modified the ensemble feedback in abundance time series simulated from age-structured populations. The statistical detection of ensemble density feedback from census data was largely unaffected by density-independent processes. Long-term population decline caused from density-independentmortalitywas the main mechanism decoupling the strength of component versus ensemble density feedbacks. Our study supports the use of simple logistic-growth models to capture long-term population trends, mediated by changes in population abundance, when survival rates are stochastic, carrying capacity fluctuates, and populations experience moderate catastrophic mortality over time.

Local fishers’ knowledge on the ecology, economic importance, and threats faced by populations of African snakehead fish, Parachanna obscura, within Côte d'Ivoire freshwater ecosystems

AbstractTraditionally, population sizes, ecology, and threats to species and their habitats have been obtained by empirical scientific studies. However, the knowledge of local and indigenous communities worldwide has been acknowledged as an extremely rich and underused source of information on how the environment, biodiversity, and local conditions are changing over time. In this view, the objective of the study was to investigate local fishers’ knowledge of local names, habitats, uses, market price, change in population abundance, and threats faced by the snakehead fish (Parachanna obscura) in Ivorian freshwaters. The study was conducted using face‐to‐face interviews and a structured questionnaire with 381 fishers during the period from October 2020 to February 2021. The results show that this fish species is strongly appreciated for the good taste of its flesh, with market prices varying between 1.5 and 3€ on average. All respondents confirmed that the species is not yet produced in aquaculture and mentioned their willingness to support its introduction into aquaculture. Several local names of P. obscura fish were recorded, with ‘Sounôgô‐djêguê’ (used in 36% of fishers’ ethnic groups), ‘Pino’ (21%), and ‘Édjoué‐bile’ (21%) being the most popular names used in Ivorian fishers’ communities. All respondents agreed that P. obscura is a potamodromous fish species living preferably in wetlands, rivers, lakes, and streams. A significant decrease in the abundance of this fish was observed by 71% of fishers, perceived mainly due to overfishing, deforestation around watersheds, habitat destruction/modification, obnoxious fishing practices, pesticide use in farms close to watersheds, and climate change, especially lack of rainfall. The study clearly demonstrated the importance of local ecological knowledge of fishers in identifying threats to fish populations, habitat types used by the species, and other relevant information; therefore, this ecological knowledge has to be integrated into biomonitoring and conservation policy of aquatic biodiversity. The information obtained from this study is also helpful for future studies on the management and cultivation of this species.

Migration chronology and multi-scale habitat selection of wintering midcontinent greater white-fronted geese

Food resources are assumed to limit waterfowl populations in the Mississippi Alluvial Valley, thus bioenergetic models are used for spatial allocation of food resources to provide adequate energy to support regional waterfowl population objectives. Changes in population abundance and distributions of midcontinent greater white-fronted geese Anser albifrons have implications for region-specific conservation planning of energetic resources for wintering waterfowl. This research aimed to quantify timing of arrival of greater white-fronted geese to wintering areas and quantify foraging behaviors. These data can help refine bioenergetics models and facilitate future waterfowl habitat planning efforts in the region. Bioenergetics models account for energetic demands of wintering geese by assuming they forage in flooded habitats 25% of the time across a 110-day winter planning period. Although this assumption has gone untested, our estimate of time spent foraging in flooded habitats (27.4% ± 5.8%) confirms the current model parameter of 25% of the time. However, we suggest that this is not the best parameter to use in bioenergetics models as greater white-fronted geese in our study foraged in dry habitats (72.6% ± 5.8%) more often than in flooded habitats. In addition, selection for rice fields in heavily weighted toward early winter (November; β = 2.85), and use declined 70% as winter progressed (February; β = 0.89), likely due to depletion of available rice grain, hunting pressure, and the physiological need to switch from a greater carbohydrate diet to a nitrogen-rich diet. In addition, white-fronted geese arrived to wintering areas earlier than current models accounted for with a mean arrival date of 30 October (± 2.5 days) to the Mississippi Alluvial Valley. We suggest early arrival to the wintering area and greater selection for dry rice fields during early winter indicates exploitative competition by white-fronted geese for shared food resources that may not be adequately accounted for in current bioenergetics models. We suggest current models underestimated energetic demands and the competitive nature of early migratory greater white-fronted geese.

Modeled distribution shifts of North American birds over four decades based on suitable climate alone do not predict observed shifts

As climate change alters the global environment, it is critical to understand the relationship between shifting climate suitability and species distributions. Key questions include whether observed changes in population abundance are aligned with the velocity and direction of shifts predicted by climate suitability models and if the responses are consistent among species with similar ecological traits. We examined the direction and velocity of the observed abundance-based distribution centroids compared with the model-predicted bioclimatic distribution centroids of 250 bird species across the United States from 1969 to 2011. We hypothesized that there is a significant positive correlation in both direction and velocity between the observed and the modeled shifts. We then tested five additional hypotheses that predicted differential shifting velocity based on ecological adaptability and climate change exposure. Contrary to our hypotheses, we found large differences between the observed and modeled shifts among all studied bird species and within specific ecological guilds. However, temperate migrants and habitat generalist species tended to have higher velocity of observed shifts than other species. Neotropical migratory and wetland birds also had significantly different observed velocities than their counterparts, which may be due to their climate change exposure. The velocity based on modeled bioclimatic suitability did not exhibit significant differences among most guilds. Boreal forest birds were the only guild with significantly faster modeled-shifts than the other groups, suggesting an elevated conservation risk for high latitude and altitude species. The highly idiosyncratic species responses to climate and the mismatch between shifts in modeled and observed distribution centroids highlight the challenge of predicting species distribution change based solely on climate suitability and the importance of non-climatic factors traits in shaping species distributions.

The long-term effect of over-supplementation on recovered populations: why restraint is a virtue

AbstractWe present a long-term analysis of the results of the Apollo butterflyParnassius apollorecovery project in the Pieniny National Park, southern Poland, using a classical population ecology model. Six possible theoretical models of changes in population abundance were constructed and their predictions compared with current data. Models that did not take into account supplementation with captive-reared individuals provided the best fit to the population growth pattern during recovery. This was probably because of the introduction of captive-reared specimens to sites while habitat reconstruction was taking place. In addition, we provide data supporting the hypothesis that a significant reduction in the habitat's carrying capacity occurred during the restoration project, probably as a result of the population being over-supplemented with captive-reared individuals. Our analysis shows that for a recovery project to be successful, captive breeding and habitat restoration should be properly coordinated.

Variable coverage in an Autocidal Gravid Ovitrap intervention impacts efficacy of Aedes aegypti control.

Control of the arboviral disease vector Aedes aegypti has shown variable levels of efficacy around the globe. We evaluated an Autocidal Gravid Ovitrap (AGO) intervention as a stand‐alone control tool for population suppression of A. aegypti in US communities bordering Mexico.We conducted a cluster randomized crossover trial with weekly mosquito surveillance of sentinel households from July 2017 to December 2018. The intervention took place from August to December of both years. Multilevel models (generalized linear and additive mixed models) were used to analyse the changes in population abundance of female A. aegypti.We observed that female populations were being suppressed 77% (2018) and four times lower outdoor female abundance when AGO coverage (number of intervention AGO traps that surrounded a sentinel home) was high (2.7 AGOs/house). However, we also observed that areas with low intervention AGO coverage resulted in no difference (2017) or slightly higher abundance compared to the control. These results suggest that coverage rate might play a critical role on how populations of female A. aegypti are being modulated in the field. The lack of larval source habitat reduction and the short duration of the intervention period might have limited the A. aegypti population suppression observed in this study. Synthesis and applications. The mosquito, A. aegypti, is a public health concern in most tropical and subtropical regions. With the rise of insecticide resistance, the evaluation of non‐chemical tools has become pivotal in the fight against arboviral disease transmission. Our study shows that the AGO intervention, as a stand‐alone control tool, is limited by its coverage in human settlements. Vector control programmes should consider, that if the target coverage rate is not achieved, measures will be ineffective unless coupled with other control approaches. Although our multilevel modelling was focused on A. aegypti and the AGO, the approach can be applied to other mosquito vector species.

Caution Is Needed When Using Niche Models to Infer Changes in Species Abundance: The Case of Two Sympatric Raptor Populations.

Simple SummaryThis study focuses on sympatric populations of hen harrier (Circus cyaneus) and Montagu’s harrier (Circus pygargus) breeding in mountain heathlands in the NW Iberian Peninsula. These populations have been affected by habitat loss caused by land-use change. Despite the mounting evidence supporting positive relationships between species abundance and habitat suitability, the capacity of ecological niche models to capture variations in population abundance remains largely unexplored. This study shows that habitat suitability predicted from niche models was significantly correlated with the relative abundance for hen harrier and, to a lesser extent, for Montagu’s harrier. However, the temporal variation in local population abundance was not significantly explained by habitat suitability changes predicted by the niche models. These findings call for caution in the use of niche models to infer changes in population abundance. The positive relationship between species abundance and habitat suitability supports the use of niche models to estimate abundance but does not guarantee the ability of these models to predict temporal variations in species abundance. These findings highlight (1) the need to include other possible biotic or abiotic factors involved in population abundance dynamics into niche models and (2) the need to establish specific monitoring protocols for tracking population dynamics.Despite the mounting evidence supporting positive relationships between species abundance and habitat suitability, the capacity of ecological niche models (ENMs) to capture variations in population abundance remains largely unexplored. This study focuses on sympatric populations of hen harrier (Circus cyaneus) and Montagu’s harrier (Circus pygargus), surveyed in 1997 and 2017 in an upland moor area in northwestern Spain. The ENMs performed very well for both species (with area under the ROC curve and true skill statistic values of up to 0.9 and 0.75). The presence of both species was mainly correlated with heathlands, although the normalized difference water index derived from Landsat images was the most important for hen harrier, indicating a greater preference of this species for wet heaths and peat bogs. The findings showed that ENM-derived habitat suitability was significantly correlated with the species abundance, thus reinforcing the use of ENMs as a proxy for species abundance. However, the temporal variation in species abundance was not significantly explained by changes in habitat suitability predicted by the ENMs, indicating the need for caution when using these types of models to infer changes in population abundance.

A polyphagous, tropical insect herbivore shows strong seasonality in age-structure and longevity independent of temperature and host availability

Bactrocera tryoni is a polyphagous fruit fly that is predicated to have continuous breeding in tropical and subtropical Australia as temperature and hosts are not limiting. Nevertheless, in both rainforest and tropical agricultural systems, the fly shows a distinct seasonal phenology pattern with an autumn decline and a spring emergence. Temperature based population models have limited predictive capacity for this species and so the driver(s) for the observed phenology patterns are unknown. Using a demographic approach, we studied the age-structure of B. tryoni populations in subtropical Australia in an agricultural system, with a focus on times of the year when marked changes in population abundance occur. We found that the age-structure of the population varied with season: summer and autumn populations were composed of mixed-age flies, while late-winter and early-spring populations were composed of old to very old individuals. When held at a constant temperature, the longevity of adult reference cohorts (obtained from field infested fruits) also showed strong seasonality; the adults of spring and early autumn populations were short-lived, while late autumn and late winter adults were long-lived. While still expressing in modified landscapes, the data strongly suggests that B. tryoni has an endogenous mechanism which would have allowed it to cope with changes in the breeding resources available in its endemic monsoonal rainforest habitat, when fruits would have been abundant in the late spring and summer (wet season), and rare or absent during late autumn and winter (dry season).

Incorporating vertical distribution in index standardization accounts for spatiotemporal availability to acoustic and bottom trawl gear for semi-pelagic species

AbstractAbundance indices from scientific surveys are key stock assessment inputs, but when the availability of fish varies in space and time, the estimated indices and associated uncertainties do not accurately reflect changes in population abundance. For example, indices for many semi-pelagic species rely on acoustic and bottom trawl gear that differ in water column coverage, and so spatiotemporal trends in fish vertical distribution affect the availability of fish to each gear type. The gears together cover the whole water column, and so in principle allow estimation of more accurate, combined indices of the whole population. Here, we extend previous methods and develop a vertically integrated index, which accounts for spatiotemporal correlation and works with data unbalanced spatially or unpaired from distinct surveys. Using eastern Bering Sea walleye pollock (Gadus chalcogrammus) as an example, we identified clear spatial and temporal patterns in vertical distribution and gear availability from 2007 to 2018. Estimated acoustic annual vertical availability ranged from 0.339 to 0.888 among years, and from 0.588 to 0.911 for the bottom trawl survey. Our results highlight the importance of accounting for the spatiotemporal and vertical distribution of semi-pelagic fish to estimate more accurate indices, and provide important context for gear availability.

Selective logging reduces body size in omnivorous and frugivorous tropical forest birds

Selective logging is the main anthropogenic disturbance in tropical forests, driving shifts in species abundances. Body size and body condition are important metrics of fitness that may be affected by habitat degradation. We conducted a four-year study to investigate how selective logging impacted the body size and body condition index (BCI) of 55 Bornean bird species and whether changes in body metrics were associated with shifts in relative population abundance. Frugivorous and omnivorous birds had reduced body size in selectively logged versus unlogged forest, but we found no evidence for selective removal of individuals driven by sex differences or post-fledging body size, indicating different developmental conditions for frugivores and omnivores in logged forest. Change in body size between forest types showed no clear patterns for insectivorous birds, and did not differ between IUCN categories. BCI of birds was affected by study year, suggesting an effect of climatic conditions on food availability, but not by logging. At the community level, post-logging change in population abundance was not associated with reduced body size, although between species variation suggests that adverse environmental conditions and different coping strategies underlie body size reductions in logged forest. Our study suggests that body size is a valuable metric to assess how logging impacts forest birds, pointing towards potential functional consequences related to seed dispersal within logged forests and need for improved silvicultural practices.

Do changes in skull size of South American sea lions reflect changes in population density?

AbstractPopulations of the South American sea lion (SASL, Otaria byronia) have been intensely exploited for leather and oil in different parts of its distribution range throughout the 19th and 20th centuries, generating large changes in abundance. In Patagonia, the SASL population was reduced by more than 90% of its original abundance, and it began to recover after sealing ended. The aim of this work was to assess changes in size and shape of the skull related to changes in population abundance during the last 100 years. Using geometric morphometry techniques, we analyzed 145 individuals (68 males and 77 females) from Patagonia. Skulls were classified by sex, time period (harvest vs. postharvest), and decades of individual's birth. Results indicated that there were differences in skull size but not in shape discriminated by time period. Moreover, individuals of the postharvest period showed a decrease in the skull size during the last two decades, coinciding with the recovery in population abundance. Our results suggest the existence of a density‐dependence response in somatic growth of SASL population of Patagonia.

Effects of environmental factors on reef fish assemblage structure in the southeastern US Atlantic

Environmental variation influences fish assemblage structure; however, fish assemblage composition shifts due to natural or anthropogenic stressors have been observed in marine ecosystems worldwide, altering ecosystem structure and function, and fisheries sustainability. Previous research in waters off North and South Carolina (USA) was limited in scope and repeatability or did not quantify fish assemblages at a scale suitable for monitoring composition shifts. Concurrent chevron traps, underwater video, and environmental data from an annual fishery-independent survey were used to characterize the environment and enumerate demersal reef fishes caught in the traps, and priority fish species observed in video in depths ~15-110 m. Multivariate analyses detected assemblage patterns and environmental influences. An 8-variable (distance to shelf edge, depth, consolidated substrate size, latitude, percent biotic cover, temperature, undercut height, biotic class) model predicted assemblages, while 4 variables explained the greatest variation (distance to shelf edge [19%], depth [15%], consolidated substrate vertical relief [4%], size [4%]). The largest number of discriminator species occurred in mid- to outer shelf areas with greater substrate complexity (i.e. increasing substrate size and relief). Assemblages dominated by Centropristis striata at depths (~15-40 m) with little substrate complexity transitioned towards assemblages dominated by Pagrus pagrus, higher prevalence of larger-bodied predators, and invasive Pterois spp. at depths (~40-110 m) with greater substrate complexity. Understanding baseline assemblage characteristics and natural drivers of variability in fish assemblage structure is vital to conservation and management efforts that monitor changes in population abundance, the presence/absence of key species, and stressor-induced modifications of local assemblages, which are all measures of ecological health that underpin comprehensive assessments and management.

Passive Acoustic Monitoring of Chaco Chachalaca (Ortalis canicollis) Over a Year: Vocal Activity Pattern and Monitoring Recommendations

Chaco Chachalaca ( Ortalis canicollis) is a declining Neotropical bird, for which our current knowledge about its natural history is very limited. Here, we evaluated for first time the utility of passive acoustic monitoring, coupled with automated signal recognition software, to monitor the Chaco Chachalaca, described the vocal behavior of the species across the diel and seasonal cycle patterns, and proposed an acoustic monitoring protocol to minimize error in the estimation of the vocal activity rate. We recorded over a complete annual cycle at three sites in the Brazilian Pantanal. The species was detected on 99% of the monitoring days, proving that this technique is a reliable method for detecting the presence of the species. Chaco Chachalaca was vocally active throughout the day and night, but its diel activity pattern peaked between 0500 and 0900. The breeding season of Chaco Chachalaca in the Brazilian Pantanal, based on seasonal changes in vocal activity, seems to occur during the last months of the dry season, with a peak in vocal activity between August and October. Our results could guide future surveys aiming to detect the presence of the species, both using traditional or acoustic surveys, or to evaluate changes in population abundance using passive acoustic monitoring, for which recorders should be left in the field for a minimum period of nine days to obtain a low-error estimate of the vocal activity of the species. Our results suggest that passive acoustic monitoring might be useful, as a complementary tool to field studies, for monitoring other cracids, a family with several threatened species that are reluctant to human presence.

The reproductive value of large females: consequences of shifts in demographic structure for population reproductive potential in Chinook salmon

While conservation and fisheries management are often concerned with changes in population abundance and distribution, shifts in population age–size structure are commonly observed in response to human and environmental stressors. Chinook salmon (Oncorhynchus tshawytscha) have experienced widespread declines in mean age and size throughout their North American range. We investigated the consequences of declines in body size for spawner reproductive potential in terms of total egg mass per female. Our case study is the Yukon River where Chinook salmon have supported subsistence, commercial, and recreational fisheries. Using historical observations on individual body size from throughout the Yukon River and the relationship between female size and total egg mass from the Canadian portion, we estimate a decline in average female reproductive potential of 24%–35% since the 1970s. Because spawner abundances and the population sex ratio have not shown clear trends over time, our results suggest a reduced total population reproductive potential. Changes in spawner quality should be considered when developing management reference points, and conservation of population demographic structure may be necessary to sustain productive Chinook salmon systems.

The unknown Baranov. Forty years of polemics over the formal theory of the life of fishes

Abstract The year 2018 marked the 100th anniversary of the publication of paper “On the question of the biological basis of fisheries” by F.I. Baranov considered a cornerstone paper of modern fishery science. Baranov formalized population dynamics by describing changes in population abundance using differential equations, introducing the concept of instantaneous fishing and natural mortality rates, and developing his catch equation, which is the foundation of most modern age-structured stock assessment models. Baranov was the first to show the effect of fishing on population structure based on theoretical grounds. At the time of its publication, Baranov’s paper did not receive much attention in Russia and was completely unknown to scientists in the West. The second publication (On the question of the dynamics of the fishing industry, 1925) received substantial criticism from many and sparked a furious debate between Baranov and his opponents that lasted for several decades. The history and content of those debates, expressed in multiple papers by Baranov, is still largely unknown. I describe the essence of arguments by Baranov and his opponents. The story of these scientific debates reveals how different philosophical concepts and dominant points of view evolved through time.

Using density surface models to estimate spatio‐temporal changes in population densities and trend

Precise measures of population abundance and trend are needed for species conservation; these are most difficult to obtain for rare and rapidly changing populations. We compare uncertainty in densities estimated from spatio–temporal models with that from standard design‐based methods. Spatio–temporal models allow us to target priority areas where, and at times when, a population may most benefit. Generalised additive models were fitted to a 31‐year time series of point‐transect surveys of an endangered Hawaiian forest bird, the Hawai‘i ‘ākepa Loxops coccineus. This allowed us to estimate bird densities over space and time. We used two methods to quantify uncertainty in density estimates from the spatio–temporal model: the delta method (which assumes independence between detection and distribution parameters) and a variance propagation method. With the delta method we observed a 52% decrease in the width of the design‐based 95% confidence interval (CI), while we observed a 37% decrease in CI width when propagating the variance. We mapped bird densities as they changed across space and time, allowing managers to evaluate management actions. Integrating detection function modelling with spatio–temporal modelling exploits survey data more efficiently by producing finer‐grained abundance estimates than are possible with design‐based methods as well as producing more precise abundance estimates. Model‐based approaches require switching from making assumptions about the survey design to assumptions about bird distribution. Such a switch warrants consideration. In this case the model‐based approach benefits conservation planning through improved management efficiency and reduced costs by taking into account both spatial shifts and temporal changes in population abundance and distribution.

Métodos de monitoreo de adultos del picudo de los cítricos Compsus viridivittatus (Coleoptera: Curculionidae: Entiminae)

Se evaluó la eficiencia de dos métodos de monitoreo de adultos de Compsus viridivittatus, considerado plaga de cítricos en regiones de Colombia: lona al piso (LP), de uso potencial en la detección de poblaciones de adultos en el árbol, y la trampa tipo cono (TE) para poblaciones jóvenes emergentes del suelo. Los estudios se realizaron en cuatro parcelas independientes en Caicedonia (Valle del Cauca, Colombia), durante 51 semanas, en un diseño completamente al azar con 20 repeticiones/método/parcela/localidad. El esfuerzo de muestreo en todas las localidades ascendió a 160 árboles-semana. Se obtuvo un total de 1961 adultos emergentes (1.363 hembras: 598 machos) con TE y 5.060 adultos (3.117 hembras: 1.943 machos) con LP. Los mayores promedios de capturas ocurrieron en periodos de máximas precipitaciones (60-103 mm/semana), 2,5 adultos en TE y 5 adultos LP. Se encontraron diferencias significativas en la abundancia de poblaciones entre parcelas; LP: rango: 10-24 adultos y con TE rango: 4-20 adultos/trampa. Las correlaciones de 66 % entre métodos/parcela, sugieren que los cambios que experimenta la abundancia de poblaciones pueden ser explicados con la dinámica que presentan las poblaciones que emergen del suelo. En síntesis, los resultados indican que el uso independiente y/o combinando de los métodos, pueden ser útil como criterio en la toma de decisiones sobre la época y el tipo de alternativa a implementar para la reducción de las poblaciones de C. viridivittatus.