Pollution and phenology

The most alarming of all man's assaults upon the environment is the contamination of air, earth, rivers, and sea with dangerous and even lethal materials. This pollution is for the most part irrecoverable; the chain of evil it initiates not only in the world that must support life but in living tissues is for the most part irreversible. - Rachel Carson

The above quote is taken from Carson's Silent Spring, published in 1963 but sadly still relevant today. Arguably, climate change has overtaken pollution as a concern for the environmentalism movement.

I was wondering about other environmental changes associated with urbanisation which led me to consider the effect of car exhaust fumes on phenology. Vehicular emissions are the major source of air pollution in urban environments (Brophy et al. 2007). These are mostly made up of nitric oxide (NO) and nitrogen dioxide (NO₂).

Car exhaust fumes. Source: the times

Honour et al. (2009) simulated air pollution in roadside, urban environments using a diesel generator fumigation system to see the effect it would have on some herbaceous plants. Their fumigation system emitted lots of different chemicals, not just one or two, which made it like pollution in a real urban environment. Their study was carried out for 3 years. Overall, they found that senescence was brought forward and flowering was delayed compared with the control group.

Hieracium pilosella. Source: wikipedia

Traffic is also a major contributor to heavy metal contamination in soils in urban and roadside environments (Zereini et al., 2007). Ryser and Sauder (2006) found that heavy metal contamination of soils delayed flowering phenology in Hieracium pilosella. They found that flowering phenology was highly sensitive to metal contamination, being affected at very low levels.

Urbanisation (again)

I found a study by Dominoni et al. (2013) which looked at the reproductive phenology of blackbirds (Turdus merula) (Fig. 1) and how this is affected by artificial light. They found that birds affected by night light developed their reproductive system and moulted earlier than those which were not exposed to light. I was interested in this because they used experimental conditions to determine the effect of artificial light, so we can be sure that it wasn't temperature having the effect.

Fig. 1. Male blackbird. Source: http://shropshirebirder.co.uk/blackbird.html

I was thinking there are probably many unaccounted for factors in studies the effects of urbanisation on phenology. Wherever there is a city there will be increased temperatures, light pollution, sources of food, pollution... I'm struggling to find papers that actually separate these effects.

For instance I found this paper by Schoech and Bowman (2008) looking at the reproductive phenology of Florida Scrub-Jays (Aphelocoma coerulescens) (Fig. 2). Those birds from suburban habitats breed sooner in the year. I wrote about how this is makes animals more competitive in a previous post. The authors measured plasma levels of protein, etc. in birds and found it to be higher in the suburban birds vs the rural birds. They inferred from this that earlier breeding is caused by the availability of protein. I think it's good evidence for differences in diet between the two populations. And, they've collected data showing that breeding phenology varies between the two populations. Their results are consistent with their hypothesis that food availability would cause earlier breeding. But, I don't think that necessarily proves the connection because any field study like this will be too confounded.

Fig. 2. Florida Scrub-Jay. Such a beautiful bird! Source: http://barbrichphotography.blogspot.co.uk/2011/05/backyard-birding.html

In fact, the authors found that leutanizing hormone was also elevated in birds. Leutanising hormone is part of the reproductive physiology of birds, the cycle of which is connected to day length (Sharp et al. 1998). Maybe light pollution could have something to do with it, too?

Urbanisation - light pollution vs urban heat island

Light pollution and the urban heat island are both associated with urbanisation. Since blogging about these I've been wondering how studies can be sure they're really seeing the effect of one or the other on phenology.

During winter birds need to get up early to start feeding, as they use their energy up overnight, and need to eat or they'll die of starvation. Ockendon et al. (2009) separated the urban heat island from effects of light pollution by hypothesis testing. In urban areas, they could get up later if it's warmer because they won't have used as much energy up over night staying warm, or they could get up earlier and start feeding sooner because there are artificial sources of light. They found birds appearing at garden feeders later in the a.m. in urban areas in Britain than in rural ones - pointing towards the urban heat island. They also found a statistically significant difference between the response of species, something you might expect if you've been following this blog. They thought the Eurasian collared dove might be getting up to feed earlier because of competition from feral pigeons (Fig. 1).

Fig. 1.

Time between first light and a bird being seen at a feeder (time relative to start; TRS) for the ten most commonly seen species. From Ockendon et al. (2009)

They used modelling to show that urbanisation, defined as the percentage of the surrounding 1 km square classified as urban/suburban, is statistically significant as a predictor variable for time of first bird arrival. However, they did not separate the effects of light pollution and temperature...

Phenology and light pollution (part 2)

Part 2!

Plants
Currently there are no studies on plant phenology and light pollution (Neil and Wu,2006). Although I found this dodgy paper on light pollution impact on tree autumn phenology that reads like it was written by a child and hasn't got proper references

Moths
van Geffen et al. (2014) found that artificial light causes the male Mamestra brassicae (Fig. 1) caterpillar to pupate earlier, The females don't experience this. Differences in pupation duration are strong - by the time the adult moths from the control sample (dark) emerged, after 110 days, ~85% the light polluted moths had already emerged.

Fig. 1 Mamesra brassicae moth

I think there is generally not as much research on light pollution and phenology as compared with temperature and phenology.

Phenology and light pollution (part 1)

We've heard about the Urban Heat Island effect before where plant phenology is affected by increased temperatures around urban areas. But, different species' phenologies are affected by many factors other than temperature. In this post and the next one I'll look at how light pollution can affect phenologies (Fig. 1).

Fig. 1 From Light Cities: Sea Level by David Stephenson (2012)

Birds
Light pollution can affect bird migration, but can't really affect the timing (phenology). Interestingly, some migratory birds are guided by stars in the night sky, and light pollution confuses them on their way and they can collide into each other and die (Longcore and Rich, 2004; Poot et al., 2008)!

Zooplankton
Aquatic invertebrates move up and down the water column in response to changing light conditions over 24 hours, something called "diel vertical migration" (Gliwicz 1986; cited in Longcore and Rich, 2004). Daphnia is an aquatic invertebrate (Fig. 2). Moore et al. (2000 cited in Longcore and Rich, 2004) found that the range of its diel vertical migration is affected by artifical light sources.

from http://www.micromagus.net/microscopes/pondlife_cladocera.html

More next time...