Short-term studies underestimate 30-generation changes in a butterfly metapopulation

Most studies of rare and endangered species are based on work carried out within one generation, or over one to a few generations of the study organism. We report the results of a study that spans 30 generations (years) of the entire natural range of a butterfly race that is endemic to 35 km2 of north Wales, UK. Short-term studies (surveys in single years and dynamics over 4 years) of this system led to the prediction that the regional distribution would be quite stable, and that colonization and extinction dynamics would be relatively unimportant. However, a longer-term study revealed unexpectedly high levels of population turnover (local extinction and colonization), affecting 18 out of the 20 patches that were occupied at any time during the period. Modelling the system (using the 'incidence function model' (IFM) for metapopulations) also showed higher levels of colonization and extinction with increasing duration of the study. The longer-term dynamics observed in this system can be compared, at a metapopulation level, with the increased levels of variation observed with increasing time that have been observed in single populations. Long-term changes may arise from local changes in the environment that make individual patches more or less suitable for the butterfly, or from unusual colonization or extinction events that take metapopulations into alternative states. One implication is that metapopulation and population viability analyses based on studies that cover only a few animal or plant generations may underestimate extinction threats

Experimental Beetle Metapopulations Respond Positively to Dynamic Landscapes and Reduced Connectivity

Interactive effects of multiple environmental factors on metapopulation dynamics have received scant attention. We designed a laboratory study to test hypotheses regarding interactive effects of factors affecting the metapopulation dynamics of red flour beetle, Tribolium castaneum. Within a four-patch landscape we modified resource level (constant and diminishing), patch connectivity (high and low) and patch configuration (static and dynamic) to conduct a 23 factorial experiment, consisting of 8 metapopulations, each with 3 replicates. For comparison, two control populations consisting of isolated and static subpopulations were provided with resources at constant or diminishing levels. Longitudinal data from 22 tri-weekly counts of beetle abundance were analyzed using Bayesian Poisson generalized linear mixed models to estimate additive and interactive effects of factors affecting abundance. Constant resource levels, low connectivity and dynamic patches yielded greater levels of adult beetle abundance. For a given resource level, frequency of colonization exceeded extinction in landscapes with dynamic patches when connectivity was low, thereby promoting greater patch occupancy. Negative density dependence of pupae on adults occurred and was stronger in landscapes with low connectivity and constant resources; these metapopulations also demonstrated greatest stability. Metapopulations in control landscapes went extinct quickly, denoting lower persistence than comparable landscapes with low connectivity. When landscape carrying capacity was constant, habitat destruction coupled with low connectivity created asynchronous local dynamics and refugia within which cannibalism of pupae was reduced. Increasing connectivity may be counter-productive and habitat destruction/recreation may be beneficial to species in some contexts

High Temperature Triggers Latent Variation among Individuals: Oviposition Rate and Probability for Outbreaks

It is anticipated that extreme population events, such as extinctions and outbreaks, will become more frequent as a consequence of climate change. To evaluate the increased probability of such events, it is crucial to understand the mechanisms involved. Variation between individuals in their response to climatic factors is an important consideration, especially if microevolution is expected to change the composition of populations.Here we present data of a willow leaf beetle species, showing high variation among individuals in oviposition rate at a high temperature (20 °C). It is particularly noteworthy that not all individuals responded to changes in temperature; individuals laying few eggs at 20 °C continued to do so when transferred to 12 °C, whereas individuals that laid many eggs at 20 °C reduced their oviposition and laid the same number of eggs as the others when transferred to 12 °C. When transferred back to 20 °C most individuals reverted to their original oviposition rate. Thus, high variation among individuals was only observed at the higher temperature. Using a simple population model and based on regional climate change scenarios we show that the probability of outbreaks increases if there is a realistic increase in the number of warm summers. The probability of outbreaks also increased with increasing heritability of the ability to respond to increased temperature.If climate becomes warmer and there is latent variation among individuals in their temperature response, the probability for outbreaks may increase. However, the likelihood for microevolution to play a role may be low. This conclusion is based on the fact that it has been difficult to show that microevolution affect the probability for extinctions. Our results highlight the urge for cautiousness when predicting the future concerning probabilities for extreme population events

Subsidized Common Agricultural Policy grazing jeopardizes the protection of biodiversity and Natura 2000 targeted species

In Europe, Natura 2000 sites should protect threatened target species and networks of habitats. The management of Natura 2000 grasslands is often financed by subsidized grazing as part of the Common Agricultural Policy (CAP). We studied the extent of CAP grazing for Natura 2000 management and how this affects a butterfly target species (the marsh fritillary) and floral resources. Based on extensive capture-mark-release studies from 2 years in >550 ha grid cells in a 225 km(2) landscape in Sweden that includes 15 Natura 2000 sites, we compared marsh fritillary occurrence probabilities and population densities in ungrazed and CAP-grazed habitats. Moreover, we analyzed how nectar resources and orchids were affected by CAP grazing based on plants records from 2347 sample plots. We estimated the proportion of butterfly habitats that were CAP-grazed within and outside Natura 2000 sites. In total, 10 453 and 4417 butterflies were marked in 2017 and 2019, respectively. The grid cell occurrence probability was 1.8 times higher and the population density was 2.3 times higher in ungrazed compared with CAP-grazed habitats in 2017, and the corresponding numbers for 2019 were 10 and 5.3 times higher, respectively. The number of flowering plants were on average 6.9 times higher and the density of orchids was 12.3 times higher in ungrazed habitats. Roughly, 30% (130 ha) of the marsh fritillary habitat was CAP grazed, and 97% of this grazing occurred within protected areas, of which 111 ha was situated within Natura 2000 area where the marsh fritillary is the target species. Alarmingly, we show that intense yearly CAP grazing, which is the dominant management strategy in all Natura 2000 sites, has devastating consequences for the target species and other aspects of biodiversity. Less intense management, which would benefit biodiversity, requires changes in the CAP, to allow more flexible payments for habitat management objectives and conservation of target species

Subsidized Common Agricultural Policy grazing jeopardizes the protection of biodiversity and Natura 2000 targeted species

In Europe, Natura 2000 sites should protect threatened target species and networks of habitats. The management of Natura 2000 grasslands is often financed by subsidized grazing as part of the Common Agricultural Policy (CAP). We studied the extent of CAP grazing for Natura 2000 management and how this affects a butterfly target species (the marsh fritillary) and floral resources. Based on extensive capture-mark-release studies from 2 years in &amp;gt;550 ha grid cells in a 225 km(2) landscape in Sweden that includes 15 Natura 2000 sites, we compared marsh fritillary occurrence probabilities and population densities in ungrazed and CAP-grazed habitats. Moreover, we analyzed how nectar resources and orchids were affected by CAP grazing based on plants records from 2347 sample plots. We estimated the proportion of butterfly habitats that were CAP-grazed within and outside Natura 2000 sites. In total, 10 453 and 4417 butterflies were marked in 2017 and 2019, respectively. The grid cell occurrence probability was 1.8 times higher and the population density was 2.3 times higher in ungrazed compared with CAP-grazed habitats in 2017, and the corresponding numbers for 2019 were 10 and 5.3 times higher, respectively. The number of flowering plants were on average 6.9 times higher and the density of orchids was 12.3 times higher in ungrazed habitats. Roughly, 30% (130 ha) of the marsh fritillary habitat was CAP grazed, and 97% of this grazing occurred within protected areas, of which 111 ha was situated within Natura 2000 area where the marsh fritillary is the target species. Alarmingly, we show that intense yearly CAP grazing, which is the dominant management strategy in all Natura 2000 sites, has devastating consequences for the target species and other aspects of biodiversity. Less intense management, which would benefit biodiversity, requires changes in the CAP, to allow more flexible payments for habitat management objectives and conservation of target species.Funding Agencies|Cementa ABHOGANAS ABStatisticon AB; Oscar and Lili Lamms Foundation [FO2018 0027]; FormasSwedish Research Council Formas [2018-02846]</p

Effects of patch quality and network structure on patch occupancy dynamics of a yellow-bellied marmot metapopulation

1. The presence/absence of a species at a particular site is the simplest form of data that can be collected during ecological field studies. We used 13 years (1990-2002) of survey data to parameterize a stochastic patch occupancy model for a metapopulation of the yellow-bellied marmot in Colorado, and investigated the significance of particular patches and the influence of site quality, network characteristics and regional stochasticity on the metapopulation persistence. 2. Persistence of the yellow-bellied marmot metapopulation was strongly dependent on the high quality colony sites, and persistence probability was highly sensitive to small changes in the quality of these sites. 3. A relatively small number of colony sites was ultimately responsible for the regional persistence. However, lower quality satellite sites also made a significant contribution to long-term metapopulation persistence, especially when regional stochasticity was high. 4. The northern network of the marmot metapopulation was more stable compared to the southern network, and the persistence of the southern network depended heavily on the northern network. 5. Although complex models of metapopulation dynamics may provide a more accurate description of metapopulation dynamics, such models are data-intensive. Our study, one of the very few applications of stochastic patch occupancy models to a mammalian species, suggests that stochastic patch occupancy models can provide important insights into metapopulation dynamics using data that are easy to collect