|
|
Reasons for the global decline of insect populations
Váňová, Barbora ; Šípek, Petr (advisor) ; Sedláček, Ondřej (referee)
This thesis deals with the issue of global decline in insect populations. Insects are one of the most numerous and diversified groups of animals in the world. This community plays irreplaceable roles in nature, contributing to the proper functioning of the entire ecosystem. However, fairly compelling evidence has now begun to emerge of long-term insect declines around the world. These declines are caused by many causes and factors that contribute to varying degrees of decline in the abundance and diversity of insect populations, and are often interrelated. The aim of this thesis is therefore to provide an overview of this global problem, and in particular its main causes. The topic has been elaborated through the study of scientific literature and subsequent presentation of the impact of individual factors on specific insect species or groups. It was found that the main reasons for the decline of insect populations are the loss of natural habitats, pollution, the spread of invasive species and pathogens, climate crisis and light pollution. Keywords: insect decline, population, biodiversity, biomass, agriculture, land use, global change
|
|
|
Raci v měnících se biotických a abiotických podmínkách
VESELÝ, Lukáš
Abiotic and biotic factors directly or indirectly influence physiology, behaviour, ecology and the distribution of organisms. This thesis provides unique results in terms of the ability of crayfish to cope with a series of these abiotic and biotic factors. Successful overwintering is key factor facilitating establishment and spread of non-indigenous species. We provide experimental evidence of substantial resistance of three out of four warm water crayfish species to the low water temperatures tested in our study. To sum up, red swamp crayfish together with yabby demonstrated high survival in experimental conditions and exhibited feeding activity even during the coldest part of the experiment. Marbled crayfish suffered high mortality, but a single specimen of survived. Redclaw is expected not to pose a risk for the European temperate zone in the near future. Drought is an important factor for freshwater organisms determining their success in a given ecosystem. One of the strategies how to survive drought are an elevated desiccation capacity and burrowing ability. We evaluated the ability of three European native and five non-native crayfish to survive and burrow in a humid sandy-clayey substrate under a simulated one-week drought. Survival of non-native species was substantially higher, being absolute in the red swamp crayfish and yabby. Red swamp crayfish and marbled crayfish constructed bigger and deeper burrows than yabby and spiny-cheek crayfish. Three native species (noble crayfish, narrow-clawed crayfish and stone crayfish) suffered extensive mortalities. The native species and signal crayfish exhibited no ability to burrow under drought conditions. Marbled crayfish are a successful invader, capable of colonization new habitats. It is also established in the wild of Ukraine and pet-traded in Eastern Europe. If released, it might pose a risk to populations of native crayfish that also inhabit saline ecosystems of the Black, Azov and Caspian Sea. We conducted the first study on salinity tolerance in marbled crayfish. In summary, marbled crayfish are probably unable to invade saline ecosystems due to its low survival, reduced growth and inhibited reproduction. Nevertheless, it showed an ability to withstand the highest salinity for an extended period of time, opening a possibility for its spread to other freshwaters via this corridor. Also, a short generation time might lead to local adaptations to saline environments in the future. Yabby demonstrated an ability to withstand simulated low winter temperatures, opening the question of its potential establishment in the region of Central Europe. To successfully do so, yabby would have to deal with present strains (A, B, and E) of Aphanomyces astaci, a causative agent of crayfish plague, a devastating disease to all crayfish not originating from North America. Our comparative study revealed the ability to survive (strain A) or delay the effects (strains B and E) of crayfish plague compared to native noble crayfish. Our result, highlights a high potential for its establishment in temperate Europe. As a prominent invader, it may cause negative impacts on entire ecosystems and contribute to the spread of crayfish plague in Europe. Nowadays, organisms face multiple global drivers influencing the strength of links in food webs. Altogether, we found that predator identity, prey density, and temperature all affect trophic and non-trophic interaction strengths. Effects of prey density were always independent of temperature and predator identity in trophic as well as non-trophic interaction strength. On the other hand, the magnitude of responses in trophic as well as non-trophic interaction strengths varied strongly across predator pairs and temperatures. Based on the current evidence, we could not find strong support for a general mechanism underlying the dependence of interaction strengths on species traits and environmental conditions. Therefore, other studies are need it.
|
guest ::
