Browsing by study line "Ecology and evolutionary biology"

After drastic declines in large carnivores’ populations globally, conservation efforts have been successful, and predators’ populations are in recovery. However, their comeback has led to new interactions with locals, generating different conflicts. Two main approaches have been considered to mitigate these conflicts, those being the land sparing and land sharing models, however, the land sparing model requires great extents of protected areas, areas that in Europe are missing, therefore forcing a call for the land sharing model. In Finland, this approach has generated debates among different stakeholders, the outcomes of this debate shaping the fate for the four species: brown bear (Ursus arctos), grey wolf (Canis lupus), Eurasian lynx (Lynx lynx) and wolverine (Gulo gulo). Attitudes towards those species can be used to explore the drivers of the conflicts, however, only few studies have explored this context, considering the ecological and social dimension separately. In addition, the ecotourism industry has been recently recognized as a new stakeholder in the Finnish large carnivore’s context, but the effects of its activities were assessed only ecologically. Therefore, with this study I aimed to explore the attitudes of locals from a specific region of Finland towards the four large carnivores’ species, and to assess the different drivers of those species, through a combination of field questionnaires, social variables and large carnivores’ population data. I explored potential correlates of the differences in attitudes, adding also the spatial effect of ecotourism over the socio-ecological factors. I predicted attitudes to vary among species, having on one side the brown bear with positive attitudes, in contrast the wolf with negative attitudes, while neutral attitudes towards the lynx and wolverine. I also expected to find more negative attitudes in smaller localities rather than in localities with a greater human population density. Also, I explored whether the ecotourism activities have a positive or negative effect over the locals’ attitude towards carnivores, expecting the ecotourism industry to bring positive attitudes in nearby localities. As result, attitudes towards the four different species varied significantly, the attitudes towards each different species having different drivers, with the human population size being important for wolverines and wolves, while the status for bear and lynx populations. The ecotourism had an effect only on bear attitudes, being positively correlated (closer the ecotourism activities were, more positive the attitudes are). To mitigate the large carnivores-human conflict in Finland, a community approach is not the solution, since the different origins of the attitudes ‘drivers. However, the attitudes among species are positively correlated, consequently, by ameliorate the attitudes towards one species, also the others will benefit. Finally, by inducing a proper management within the ecotourism industry and promoting more the respective activity on a national level, the ecotourism can have a positive impact and get a positive role in the Finnish conflict.

The intensification of agriculture is one of the main drivers of biodiversity loss worldwide. One of the intensification shifts has occurred from cattle grazing on biodiversity-rich semi-natural grasslands to ceased grazing or grazing on cultivated species-poor grasslands. While the effect of different grazing pressure on biodiversity in semi-natural grasslands has been studied extensively, little is known of how current grazing regimes on cultivated grasslands affect biodiversity and ecosystem services in different farming systems. Here, we investigated how arthropod abundance and potential ecosystem services are related to varying grazing pressure on cultivated grasslands at conventional and organic farms with meat or dairy production. We sampled aerial arthropods with sticky tape traps in four land-use types within the farms. Relative arthropod abundance was derived from the tapes using an imagery analysis, and the numbers of pollinators and predators from 4 taxonomic groups were counted. The results showed no difference in the relative arthropod abundance in relation to grazing pressure, but there was weak evidence for higher predator abundance at low and high grazing pressure. The relative arthropod abundance showed a positive trend in organic farms. However, pollinator abundance was higher in conventional farms, and predator abundance did not differ between farming systems. Land-use type was related to the occurrence of predators and pollinators: both groups had the lowest abundance in farmyards compared to cultivated pastures, silage fields, and cereal crop fields. Predator numbers were also higher in silage fields than in the other land-use types. However, there was no significant interaction between land-use types and farming systems in their effect on the arthropod groups. The results suggest that grazing pressure on cultivated grasslands has a minor or negligible impact on arthropod abundance in the two commonest farming systems. However, the effect of farming systems on relative arthropod abundance might be obscured by low sample sizes, high abundance of only a few species, and other variables not included here, such as the use of manure or pesticides. In addition, pollinators included only two taxonomic groups, potentially leading to results not applicable to all pollinators. Consequently, more large-scale studies with higher sample sizes and the inclusion of arthropod diversity and data on the key on-farm practices and landscape structure are needed to disentangle the relationship between biodiversity and grazing on cultivated grasslands in Finland.

Climate change is applying pressures to plant populations, which must adapt or move to retain fitness. A changing climate highlights the need for us to understand the potential that species possess to evolve in addition to any plastic responses. Approaches that allow the study of contemporary evolution, such as resurrection studies, have the capacity to provide insights into the responses of populations to these changes. In this resurrection experiment, seeds from seven populations of Hypericum perforatum collected from the UK and France, and their historic counterparts, were grown and subjected to four temperature treatments. Three traits were measured and compared between historic and contemporary populations: date of flowering, average seed weight and flower abundance. I found that temperature influenced date of flowering and flower abundance, leading to an overall earlier flowering time and an overall decrease in flower abundance with increase in temperature. The only significant difference between historic and contemporary populations was found in flower abundance - where, whilst flower abundance declined with increasing temperature, contemporary populations produced proportionally more flowers than historic populations per degree of temperature increase. These results suggest that plasticity allows this species to adjust its flowering phenology to retain fitness in warmer conditions but that evolution during the past decades may have selected for a decreased flower abundance at higher temperatures. These findings contribute to our overall understanding of how species have and will react under climate change, as we try to disentangle the roles that plasticity and evolution play in enabling populations to retain fitness under changing conditions.

Cities are novel and fragmented environments that offer a wide range of habitats and resources for urban dwellers, such as birds. Previous work shows that the size and vegetation structure of urban forest patches and parks play an important role in urban bird abundance and diversity. The aim of the thesis was to find out the role of major urban greenspaces and which local and landscape-scale drivers in the urban greenspace network are influencing bird species richness and composition in the city of Lahti. A breeding bird survey was conducted in Lahti, including 60 survey points and 15 urban greenspaces. A total of 41 bird species were observed, and the most common species were Fieldfare, Common Chaffinch, and Great Tit. On the local-scale, the size of trees was positively correlated with bird species richness, indicating that bigger and older trees support higher bird diversity in urban greenspaces. On the landscape-scale, I found that the size of the greenspace, its distance to the urban continuum border, and the amount of green neighbouring the greenspace were the significant drivers explaining bird species richness. The findings indicate that both local and landscape-scale drivers are significant for urban bird communities in Lahti. Furthermore, to better understand the resources that urban communities need, a comprehensive study of different urban dweller species is important – not just the few sensitive species – to achieve effective management. Urban greenspaces host most of the urban bird species in the city; thus, it is important to preserve these urban greeneries as well as protect the green areas around the city proactively to sustain them while the urban development continues sprawling.

Artificial light at night (ALAN) is an emerging environmental problem, originating from e.g. street lightning and infrastructure. It has been found to alter the behavior of many organisms and thereby influence community composition and ecosystem functions. However, most studies on the impact of ALAN on wildlife and the environment have focused on terrestrial ecosystems, while aquatic ecosystems have received less attention, yet are increasingly exposed to artificial light. Gammarus species are amphipods commonly found in freshwater and estuarian ecosystems across Eurasia and North America. They are key components of ecosystems in recycling nutrients and serving as a food source for other species. They are night active and, hence, vulnerable to ALAN. Earlier studies show that ALAN increases their predation risk and induces physiological stress. However, no study has assessed the impact of ALAN on mating behavior, although mating success is a key fitness component that influences population dynamics. Gammarus pulex is a common freshwater detritivore where females are receptive for a short period and males compete for females and then guard them through amplexus, precopulatory guarding. The aim of this master’s thesis was to study if and how ALAN affects the mating behavior of the G. pulex, and if this depends on the presence of male-male competition for females. G. pulex, individuals were collected from a stream in Helsinki and exposed to control (natural light conditions) or ALAN in the absence or presence of male competition, eight treatment combinations in total, for one week under laboratory conditions. In each trial, one female and either one or two males were placed into a tank – in the absence or presence of ALAN – and their behavior recorded for ten minutes, including active time, contact between the sexes, and pair formation and separation. The results show that ALAN influences both night and day mating behaviour, but that the effect depends on the presence of male competition. ALAN had no impact on activity during the night, while male competition decreased it. During the day, ALAN decreased activity, but male competition counteracted and increased activity. Number of contacts between female and male(s) was only impacted by male competition during the night, but by both ALAN and male competition during the day; ALAN reduced contact time during the day in the absence of male competition, while male competition increased contact time. Pair formation was negatively affected by ALAN during the night, while male competition increased formation. Pair separation was higher under ALAN during the day, independent of male competition, but unaffected at night. These results indicate that ALAN causes a carry-over effect, with light conditions during the night influencing mating behaviour during the day. This is most likely through physiological changes incurred during the night because of the artificial light, such as increased stress levels. Further studies should assess how ALAN impacts mating behavior when many individuals are present, as G. pulex is more choosy in mate selection at higher population densities. Follow up studies are also needed to determine if the effect of ALAN depends on the colour of the light, as found for other organisms, as such information is needed in conservation work aiming to reduced negative effects of ALAN on ecosystems through the development of environment friendly lighting systems. Regarding the consequences of the change in mating behaviour when exposed to ALAN, this could alter population dynamics. Given the key ecological role of the species in ecosystems, this could lead to changes in nutrient recycling and the structure of food webs. Considering that the presence and intensity of ALAN is expected to increase in the future, it is of great importance to assess its effects on organisms, not only during the night but also during the day through carry-over effects, as indicated by the present study.

Phylogenetics is the study of the evolutionary history of life on Earth, which has shifted from relying on morphological characteristics to molecular data with the advancements in sequencing technology. Understanding Earth's biodiversity is crucial, as it has important implications for conservation, ecology, and evolution. Speciation occurs when barriers restrict gene flow between previously interbreeding populations. One such barrier may be endosymbiotic bacteria, like Wolbachia, which can manipulate host reproduction and create incompatibilities between host lineages. Wolbachia is widely distributed among arthropods and is the most common endosymbiont of insects. The bacterium is known to alter its hosts' biology, serving as a master manipulator of reproduction. Wolbachia-induced phenotypes can lead to the divergence of host lineages and speciation events. The genus Cotesia (Hymenoptera: Braconidae: Microgastrinae) is a highly diverse group of parasitoid wasps, where several species parasitize Melitaeini butterflies, including two cryptic species complexes. The current phylogenies of these species are 20 years old and need an update, as they were built with few markers and contain unresolved nodes. Wolbachia has been observed in this system, but its role remains largely unexplored. In this study, I aim to reconstruct the phylogeny of Cotesia species parasitizing Melitaeini butterflies, using two mitochondrial markers and eight nuclear markers to update our understanding of the differentiation of the cryptic Cotesia species. Additionally, I screened the specimens for Wolbachia to determine its possible role in shaping the Cotesia host phylogeny. I expect different Cotesia lineages to carry divergent Wolbachia strains or have different infection statuses (infected vs. uninfected). With fresh Cotesia specimens collected from various locations in Europe, I amplified and sequenced two mitochondrial markers (16s, COI) and eight nuclear markers (18s, 28s, CfCN, CfEN, EF1A1, LwRh, SLD5, TCEB) for phylogenetic analysis. The phylogenetic analysis revealed two main clades: Clade A, where Cotesia acuminata forms a polyphyletic group, and Clade B, where Cotesia melitaearum forms a monophyletic group. Wolbachia was detected only in one species, Cotesia melitaearum Sp. G, where the strain has persisted for over 20 years. The strains infecting Cotesia belong to supergroup B and are all closely related. The close relationship and low infection rate suggest that Wolbachia is not responsible for the original divergence but may play an ongoing role in restricting gene flow between species. The updated phylogeny is in concordance with the previous works but also strengthens our understanding of the relationships within Clade B. Further work is required to resolve some relationships within Clade B and understand the cryptic species' divergence.

Nitrogen fixation by Sphagnum mosses in a boreal fen ecosystem Emmi Tuokko Master’s Programme in Ecology and Evolutionary Biology Faculty of Biological and Environmental Sciences University of Helsinki May 2022 Faculty: Faculty of Biological and Environmental Sciences Degree programme: Master’s Programme in Ecology and Evolutionary Biology Study track: Ecology and Evolutionary Biology Author: Emmi Tuokko Title: Nitrogen fixation by Sphagnum mosses in a boreal fen ecosystem Level: Master’s thesis Month and year: May 2022 Number of pages: 34 pages + 4 appendix pages Keywords: nitrogen fixation, Sphagnum, boreal fen, acetylene reduction, diazotroph Supervisor: Dr. Juha Mikola Where deposited: HELDA – Digital Repository of the University of Helsinki Abstract: Ecosystems in the North are heavily constrained by nitrogen (N) and the main pathway of N for plants is biological N2 fixation by Sphagnum mosses. Mosses fix N with either free-living, associated or symbiotic diazotrophs and convert it to a plant-accessible form. This way N2 fixation contributes significantly to the level of photosynthesis and carbon sequestration that these ecosystems can maintain. However, diazotrophs are exposed to large fluctuations in abiotic factors and earlier findings have suggested that to affect the rate of N2 fixed. Only a few studies have focused on boreal Sphagnum-dominated fens and thus, I wanted to figure out what environmental factors control N2 fixation activity in this habitat type. Most of the N2 fixing bacteria are heterotrophs but also methanotrophs have been shown to participate in N2 fixation. Therefore, I tested if methane (CH4) flux was connected to N2 fixation activity. As N is a necessary nutrient for plants, I also wanted to see whether the variation in N2 fixation can explain the variation in plant growth and productivity and on the other hand, if the productivity can explain the rate of N2 fixation by providing more energy. To test these interactions, we established the acetylene reduction assay (ARA) on a fen in Northern Finland to measure, how much N2 is fixed. We also recorded environmental factors (soil moisture, soil temperature, air temperature, relative humidity and radiation), measured CO2 and CH4 fluxes and calculated vascular plant coverage and Sphagnum growth from 20 study plots. I expected to find a correlation especially between soil moisture and N2 fixation because earlier studies have shown it to control the fixation activity the most. I found out that leaf area index (LAI) of vascular plants was explained by N2 fixation. This is a significant finding because it has not been proved before. It supports the earlier findings about the connection between N2 fixation and vascular plant photosynthesis. I also discovered that radiation (PAR) and potential gross primary production (GPP1200) explained the variation in N2 fixation in the first measurement. This shows the dependency of N2 fixation on the energy that photosynthesis provides. Contrary to my predictions, none of the other factors explained N2 fixation or were explained by N2 fixation. Further studies about moss-associated N2 fixation are needed especially in the light of future changes in climate and N deposition. Tiedekunta: Bio- ja ympäristötieteellinen tiedekunta Koulutusohjelma: Ekologian ja evoluutiobiologian maisteriohjelma Opintosuunta: Ekologia ja evoluutiobiologia Tekijä: Emmi Tuokko Työn nimi: Rahkasammalten typensidonta boreaalisessa suoekosysteemissä Työn laji: Maisterin tutkielma Kuukausi ja vuosi: 5/2022 Sivumäärä: 34 sivua + 4 sivua liitteitä Avainsanat: typensidonta, rahkasammal, boreaalinen, suo, ARA, diatsotrofi Ohjaaja: Dr. Juha Mikola Säilytyspaikka: HELDA - Helsingin yliopiston digitaalinen arkisto Tiivistelmä: Pohjoisen ekosysteemit ovat erittäin typpirajoitteisia, ja kasvit saavat suurimman osan typestä rahkasammalten biologisen typensidonnan kautta. Sammalet sitovat typpeä joko vapaana elävien tai symbionttisten diatsotrofien välityksellä ja muuttavat typen kasvien käytettävissä olevaan muotoon. Tätä kautta typensidonta vaikuttaa merkittävästi koko ekosysteemin fotosynteesin ja hiilensidonnan tasoon. Diatsotrofit ovat kuitenkin alttiita abioottisten tekijöiden suurelle vaihtelulle, ja aikaisemmat tutkimukset ovat todenneet sen vaikuttavan typensidonnan tasoon. Vain harvat näistä tutkimuksista ovat keskittyneet boreaalisiin minerotrofisiin soihin, joilla rahkasammalet dominoivat, joten halusin selvittää, mitkä ympäristötekijät kontrolloivat typensidonnan aktiivisuutta tällaisessa elinympäristössä. Suurin osa typpeä sitovista bakteereista on heterotrofeja, mutta myös metanotrofien on osoitettu osallistuvan typensidontaan. Sen vuoksi halusin tutkia, onko metaanivuo yhteydessä typensidonnan tasoon. Typen ollessa välttämätön ravinne kasveille halusin myös nähdä, voiko vaihtelu typensidonnan tasossa selittää kasvien kasvua ja tuottavuutta, ja toisaalta, voiko tuottavuus selittää typensidonnan vaihtelua tarjoamalla sille lisää energiaa. Testataksemme näitä yhteyksiä mittasimme typensidontaa asetyleenin pelkistysmenetelmällä Halssiaavalla Sodankylässä. Mittasimme myös ympäristötekijöitä (maan kosteus, maan lämpötila, ilman lämpötila, suhteellinen kosteus, säteily), hiilidioksidi- ja metaanivuota, putkilokasvien peittävyyttä ja rahkasammalten kasvua 20 tutkimusruudulta. Odotin löytäväni korrelaation erityisesti typensidonnan ja maan kosteuden väliltä, sillä aikaisemmat tutkimukset ovat todenneet kosteuden olevan merkittävin typensidontaa säätelevä tekijä. Sain selville, että typensidonta selitti ruutujen välistä vaihtelua putkilokasvien lehtipinta-alassa. Tämä on tärkeä löydös, sillä yhteyttä ei olla todistettu aiemmin. Tulos tukee aiempia löydöksiä typensidonnan ja putkilokasvien fotosynteesin yhteydestä toisiinsa. Ensimmäisten mittausten tulokset osoittivat, että säteily ja potentiaalinen bruttoperustuotanto selittivät typensidontaa. Tämä todistaa typensidonnan riippuvuuden fotosynteesin tarjoamaan energiaan. Vastoin odotuksiani muut tekijät eivät selittäneet typensidontaa, eikä typensidonta selittänyt niitä. Lisätutkimukset sammalten typensidonnasta ovat tarpeen erityisesti ilmastonmuutoksen ja lisääntyvän typpilaskeuman valossa.

Paleoekologia tutkii fossiloituneita kasveja ja eläimiä ja niiden suhdetta ympäristöönsä. Se on yksi niistä tutkimusaloista, joka pyrkii selvittämään kuinka esimerkiksi nisäkäsyhteisöjen rakenne on muuttunut aikojen kuluessa ympäristön ja muiden pitkäaikaisten muutosten seuraksena. Tämän tutkimuksen tavoitteena oli selvittää, voidaanko kehittää menetelmä, joka voisi muutamalla nisäkkäisiin liittyvällä perusmuuttujalla, kuten niiden liikkumistavalla ja ravinnolla, määrittää nisäkäslajien muodostaman yhteisön rakenne sekä sen, ovatko nämä rakenteet erilaisia eri elinympäristöjen kesken. Mikäli menetelmä toimisi nykyisten nisäkäslajien tiedoilla, voisi sitä kehittää myös paleoympäristöjen ennustamiseen. Tutkimukseen valittiin kaksi menetelmää nisäkäsyhteisöjen muodostamiseksi. Ensimmäinen menetelmä pohjautui itseorganisoituvaan kartta-algoritmiin (SOM, Self-Organizing Map). Toinen perustui nisäkkäiden ryhmittelyyn liikkumismuodon ja ravinnon perusteella. Kaikki tutkimukseen valitut muuttujat olivat sellaisia, että niitä voidaan käyttää myös paleontologisissa aineistoissa. Ensimmäisen menetelmän tuloksena voidaan todeta, että itseohjautuvan kartan käyttö nisäkäsyhteisöjen muodostamiseen ei ollut toimiva. Muodostuneet yhteisörakenteet olivat hyvin abstrakteja ja niitä oli vaikea selittää. Itseohjautuvien karttojen käyttö soveltui kuitenkin muiden rakenteiden, kuten nisäkkäiden ravintoryhmien luokitteluun. Toisen menetelmän tulokset osoittavat, että on mahdollista erottaa suurin osa maalla olevista pääelinympäristöistä niillä nisäkäsyhteisöjen rakenteilla, jotka muodostettiin lajien liikkumismuodolla ja ravinnolla. Näillä kahdella muuttujalla muodostui merkitseviä eroja eri nisäkäsyhteisöjen välillä. Nämä yhteisöt toimivat hyvin myös eri pääelinympäristöjen indikaattoreina. Osoittautui, että useassa tapauksessa alueilla, joilla oli samankaltaiset ympäristöolot, vaikka sijaitsivatkit eri mantereilla, oli samankaltaiset nisäkäsyhteisöt. Jälkimmäistä menetelmää voidaan kehittää edelleen ryhmittelemällä nisäkäsyhteisöjä myös muiden muuttujien avulla. Näitä muuttujia voisivat olla esimerkiksi nisäkkäiden koko sekä hampaiden rakenne. Kehittämällä algoritmeja, jotka laskevat erikseen elinympäristöjen indikaattoreita ja myöhemmin yhdistävät niitä voisi muodostaa vielä tarkemman mallin elinympäristöjen ennustamiseen.

Bamboos are very relevant for ecosystem dynamics in tropical and subtropical forests worldwide. Madagascar holds 35 endemic species of woody bamboo, mainly found in forested areas. Six species of bamboo lemurs endemic to the island are highly specialized to exploit such bamboo species. Bamboo lemurs are highly threatened with extinction, and recent translocations of individuals to protected areas have failed, resulting in the death or emigration of all translocated individuals. The distribution, dynamics, and conservation status of the bamboo species they depend on is poorly known, while rising deforestation rates and direct exploitation of bamboo present important threats. Remote-sensing techniques, used often to map vegetation classes over large scales can potentially be used to map the extent of bamboo in a forested area, given the distinct structural and phenological characteristics of these grasses. In this study, I integrated ecological and remote sensing approaches to understand the diversity of bamboo species in the Ranomafana region of Madagascar, and to determine whether their distribution can be mapped through remoted sensing, if their occurrence is limited to particular habitat types, whether the national park presents suitable patches of bamboo for bamboo lemurs, and whether vegetation changes over the last 15 years have diminished the potential availability of bamboo in the area. I conducted an expedition to Ranomafana National Park (RNP), in south-eastern Madagascar, in November 2023, and collected 123 vegetation plots, including 45 plots revisited after an expedition in 2008. I used this field data to train a random forest classifier conducting supervised classifications based on Sentinel-2 imagery. I used these classifications to map the extent of different vegetation types and two genera of bamboo in RNP and its surroundings and evaluated their spatial and temporal distribution. The classification model accurately predicted the distribution of genus Cathariostachys, an endemic giant bamboo which is the main food source for bamboo lemurs in Ranomafana. Plots with Cathariostachys grew in the highest densities of all bamboo assessed in the field plots, and its distribution was projected over secondary and degraded forest areas, including areas outside RNP. Instead, the distribution of the endemic climbing bamboo of genus Sokinochloa, a secondary food source for bamboo lemurs, was captured with lower accuracy, mostly in the forested areas inside RNP, where it grew in low densities in the field plots. Comparing forest extent based on remote sensed classifications from 2008 and 2023, I show that a big proportion of forest has been lost in unprotected areas. RNP provided protection against forest loss, but the promotion of primary forest conservation and the disturbances through illegal activities are likely not providing habitat to secondary forest dwelling Cathariostachys bamboo. Small, sparse Sokinochloa patches within the continuous forest can assist bamboo lemur connectivity when moving through clustered patches of Cathariostachys. Nonetheless, because bamboo lemurs are affected by poaching in unprotected areas, the availability of good-quality Cathariostachys bamboo stands inside RNP is crucial for their conservation. However, no evidence of sexual reproduction or establishment of new patches of Cathariostachys was found in the field. Therefore, habitat restoration measures focused on securing new growth of this bamboo genus inside RNP could have a great impact on the conservation of bamboo lemurs. The success of such conservation measures could be assessed remotely with the mapping model developed in this study.

Norway rats are common commensal species across the world. Despite their long history with humans, the ecology of urban rats is still relatively unknown. Which is why in my thesis, I model the population dynamics of wild urban rats of Helsinki using trap data from a professional pest management company. To protect the privacy of the company’s customers, the data are on the scale of postal code areas. Using a generalized linear mixed model, I investigate several different factors that might affect rat populations. As the data come from a pest management company, trapping factors need to be considered. Other factors include environmental, such as the proportion of parks or the type of sewer present in the postal code area. But as urban rats live in cities, anthropogenic factors such as human density and income matter too. In the span on seven and half years, 8 415 rats were trapped all across Helsinki, in some places more than others. Of all the factors only the trapping factors along with household median income were significant. Median income was negatively associated with trapped rats, so more rats were trapped in areas with lower income. Future studies should try to uncover for what unknown factor income acts as a proxy for.