Effects Of Urbanization On Wildlife Resources Biology Essay

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Abstract

This review illustrates the need to advance our ability to understand, predict, and mitigate effects of urbanization on wildlife resources.

1. Introduction

The process of urbanization often results in extensive modification of the natural environment, and confronts organisms with a range of novel conditions (Dickman and Doncaster, 1987). Over the past century an increase in human population density has resulted in an increase in the process of urbanisation and the construction of industrial developments; this in turn is effecting the natural environment in which mammals thrive. In the recent years the effect of urbanization on non-human species such as the red fox (Vulpes vulpes) has become of significant interest.

The concept that ecological interactions of animals may differ according to the type of habitat they occupy is not new (Lessells, 1991). Differences will arise depending on the nature of its habitat interactions and the life history of the animal. For example the gray squirrel (Sciurus carolinensis) is strongly affected by urban variables such as proximity to houses, artificial feeders, or other physical structures (Flyger, 1970). For small mammals such as the woodmouse (Apodemus sylvaticus), vegetation has been shown to more important when predicting population density than urban variables. This is because urban areas form a patchwork of different habitat types (i.e., woodland, scrub, garden), and for majority of their lives individuals will remain in a single habitat patch (Dickman and Doncaster, 1987).

The Red fox (Vulpus vulpus) is the most widespread and of all wild canids and can be found throughout almost the entire Northern Hemisphere and isolated parts of the Southern Hemisphere. Since the fox is so adaptable its habitat requirements vary extremely. It can be found across Europe and Asia as far south as the Himalayas. It is found in Egypt and Algeria in Africa, and Northern North America extending along the Rockies and to the Gulf coast in the United States. It has been introduced into Australia and occupies all but the Northern parts. (Hutchins at al, 2003). It is not surprising that the fox has been able to successfully adapt to an urban environment as it is an opportunistic animal that is not specialised for any particular lifestyle. With habitat changes differences between the behaviour and diet of urban and rural foxes are expected.

This review had two main objectives (1) to compare the ecological differences between rural and urban foxes and (2) to describe the variation in their diet, life cycle and behaviour by linking these variations to differences in their habitat.

2. Utilization of Urban and Rural Habitats.

The red fox is an opportunistic animal that is not over-specialized for any particular lifestyle. It can therefore thrive in a variety of locations as it has no particular habitat requirements (805). Foxes are most abundant in fragmentary habitats that offer a wide variety of food and cover. They exercise choice in selecting a place to live within the restrictions imposed by their social behaviour (Lloyd, 1980).

They are not common found in densely wooded habitats, but otherwise show great flexibility in selecting a place to live. They can live on the tundra in Alaska and in semi - desert scrub in Africa. They forage in towns and hunt in areas cleared for agriculture, that they have adapted well to humans, (Hutchins at al, 2003)

2.1. Rural Habitat.

In rural areas free of anthropogenic influence foxes have shown preference for small coniferous woodlands that afford good shelter in upland areas. Large coniferous plantations are poor foraging areas, but they are also good habitats while ground vegetation remains. In diverse habitats foxes are most abundant as most of their movements and foraging is on habitat edges (Mac Donald and Claudio Sillero - Zubiri, 2004). The preferred denning sites of the red fox are burrows of other animals. Good denning sites for this species need to be within or close to vegetative cover, near water, and in areas having a good prey base. Sites within 200 yards of free water are preferred. A good prey base close to the dens is essential because females seldom range more than 1/2 mile from their dens. The general perception of 'natural' habitat is a dry mixed landscape consisting of scrub, woodland and farmland. However, foxes are also abundant in plantations, on moorland, in mountains (above the treeline), coastal dunes and even deserts (Llyod, 1980).

Agricultural habitats form part of rural landscapes. In these areas the red fox is known to be one of the most important predators (Lloyd, 1980). When habitats shift from rural secluded areas to areas under anthropogenic influence some modification in fox ecology will occur (Goldyn, 2003). In farmland areas, wood edges and woodlots are virtually exclusive habitats where fox dens are situated (Lariviere, 1966). In farmlands adjacent to wooded areas only a minority of foxes will locate in an open habitat. This was shown by GoszczclqSrd (1985) in an area with 21% forest coverage, only 2% of all dens were located in open habitats

In Poland Goldyn (2003) found that in agricultural areas the majority of foxes show a marked preference for areas with wooded cover over open habitats such as arable land. However in farmlands where wood cover is lacking, foxes have been found to successfully adapt to completely different conditions, reaching high den - sites. Banks of drainage ditches, marsh banks and boundary strips between fields were also frequently used as den locations. Dens have a crucial meaning for foxes, not only as breeding places, but also as a shelter for adults during the whole year (Meia and Weber, 1993). Their location may be related to the distribution of food resources or the presence of adequate habitats (Goldyn, 2003).

2.2. Urban habatits..

Urban habitats have become ecosystems in which mammal populations have adapted their lifestyle in order to survive. These fragmented ecosystems provide breeding sites, food and shelter needed by mammals such as the fox (Macdonald and Newdick,1982). For the purpose of this review an 'urban habitat' will refer to any habitat within a built up area that does not occur naturally outside it. Urban habitats include gardens, parks, wastelands, road verges, railway tracks, cemeteries, etc.

There has been some confusion as to which habits are important for the urban fox. Lloyd (1968) noated that urban 'foxes may live in gardens, but usually they shelter in daytime in woodlands, parks, cemeteries, and overgrown sites such as isolated building plots'. Similarly Beams (1969, 1972) found that foxes had occupied most of the suitable areas 'containing open spaces and large gardens in the southern half of the area. However Harris (1977) found that in suburban areas the most important daytime rests are quiet gardens irrespective of their size and similar domestic habitats. Parks and public open spaces were of little importance (Table 1). Habitat variables have been shown to have consistent effects on the distribution of foxes. Foxes are most commonly found in areas of diverse habitat, or where industry, commerce or council - rented housing housing predominated (Harris and Rayner, 1986). In London suitable habitats for daytime harbourage is an important limiting factor for the distribution and numbers in fox populations (Harris, 1977).

Habitat

Number of Specimens

Percent of specimens

Percent of surburban land use

Resedential habitats - gardens, garden sheds, cellars, houses

226

59.79

40.19

Industrial habitats - sewage stations, factories, builders yards, nurseries

28

7.41

3.72

Vacant land, normally without public access

32

8.47

6.01

Parks and public open spaces

33

8.73

10.53

Hospitals

9

2.38

1.10

Allotments

20

5.29

1.29

Cemetries

10

2.65

0.74

British rail and underground lines

9

2.38

2.29

Golf courses

5

1.32

No data

Sports grounds and school fields

3

0.79

2.29

Rubbish tips

2

0.53

0.59

Airports

1

0.26

1.58

Road deaths

22

---

---

Other habitats

---

---

29.67

Totals (excluding road deaths)

378

100.00

100.00

Table 1: Harris (1977) collected 400 suburban fox corpses in London, in order to show the relative importance of the various suburban habitats as daytime harbourage. Road deaths were excluded as they do not supply such data.

In London regular disturbance is the main factor governing the distribution of breeding earths. The majority of natal sites are situated in quiet gardens and railway embankments, both of these habitats being undisturbed. Few litters are raised in areas of public access (Table 2). In Kansas the type of soil, presence of water, presence of cleared areas and absence of man were important factors influencing selection of den sites (Stanley, 1963). Scott and Selko (1939) found that the slope of den sites were also important.

Situation

Number

Percent

Under garden sheds with raised floors

36

37.1

Under concrete floors of garages, out-buildings, and raised floors of summer-houses and portable huts

10

10.3

In air-raid shelters

1

1.0

In drains

1

1.0

In banks of earth e.g. at bottom of gardens, railway embankments, etc,

29

29.9

In flat ground

9

9.3

In flower-beds, rockeries

6

6.2

In compest heaps, piles of rubbish, woodpiles

5

5.2

Total

97

100.0

Table 2: Sitting of suburban fox earths used for rearing cubs (Harris, 1977).

It has been suggested by several authors that railway lines may be a particularly important habitat for the urban fox. Radio-tracking in Edinburgh, found that the types of habitats visited largely reflected their availability, but railway lines in particular were selected by dog foxes as pathways between parts of their range (Treweila and Harris, 1990) One of the main effects of urbanisation is the fragmentation of the natural environment into smaller patchy habitats. Dispersal between patches may be facilitated by rail and canal links (Goriup 1976; Yalden 1980), but it is reduced markedly by roads (Dickman and Doncaster 1987).

Within an urban matrix foxes may also populate rural like area……phonix park

3. Effects of habitat on life cycle.

3.1 Breeding

From place to place the litter sizes of cubs born of rural foxes and the proportion of vixens that produce cubs vary; variation can also occur from one year to another year in the same place (see table 17). Some of the apparent variation is real and some is due to variability in the sample composition and size. This variation also applies to urban fox populations. The pattern of reproduction and reproductive productivity in urban areas is probably identical to that of rural areas and the variability found within and between, thus although urban foxes sometimes reveal differences in reproductive patterns, sometimes showing better performance, sometimes worse, the differences within the range of variability that can be found in rural fox populations (Lloyd, 1980).

*A direct comparison between the lengths of breeding seasons in urban and nearby rural areas has not yet been directly studied, however it does not seem unlikely that the breeding season of the fox may be extended somewhat in urban areas. The are two likely explanations for extended breeding seasons in urban habitats. Firstly urban environments provide protection from the extremes of weather. Secondly, in urban areas in winter food is not scarce, as it often is in rural areas (Harris, 1977). A study by Watts (1970) found that by increasing the food supply to populations of bank voles and wood mice the breeding season may advance by as much as three weeks.

3.2. Dispersal

October is the most likely time for fox dispersal to occur (Harris, 1988). Not all cubs will disperse, and those that disperse do not all leave in their first year. Harris (1988) found that before 1st October 10.8% of male cubs and only 3.5% of female cubs dispersed. By the end of December, 58.5% of tagged males and 32.5% of tagged females had dispersed. Most of the animals that dispersed did so by the end of their second year, the final proportions being 75.8% for males and 37.8% for females. Data on rural foxes gathered by Storm et al. (1976) indicated that most of them also disperse in October. However in the rural population the proportion of foxes dispersing they studied was somewhat higher, reaching 96% for males and 58% for females.

The most important factor affecting dispersal is probably population density. Harris (1988) found that in urban areas male cubs from small litters were less likely to disperse than male cubs from large litters. Animals from areas of low fox density were also found to disperse farther than animals from areas of high or medium fox density.

4. Dietry implacations of habitat

Although the fox is primarily a carnivore, it is a non - specialist and its diet is extremely varied. The composition of its diet is influenced by its location and the time of year. As the fox is both a predator and a scavenger, it is presented with a huge variety of prospective foods (Lloyd, 1980). Foxes are known to switch their diet in response to prey population changes, such that they feed on what ever is abundant locally. This is reflected by differences between urban and rural fox diet.

In rural food studies medium sized animals (mainly rabbits) have been found to dominate in their diet throughout all seasons (62). Following an outbreak of myxomatosis in Brittan (1258) the importance of rabbits in their diets decreased and field voles increased (786). However the intake of small rodents in Northern Ireland was much lower then in Britain at this time, it is therefore possible that rats, hares and rabbits are of greater importance to the rural Irish fox because of the restricted variety of mammalian prey (Fairley, 1970a). Fruits and berries are also of seasonal importance to the rural fox, especially in the early autumn. Foxes will take blackberries, raspberries, bilberries, cherries, hawthorn berries and where they are able to strawberries in great quantaties in the summer (Llyod, 1980). Lever (1959) also identified earthworms, slugs and snails as constituting a small proportion of the food of the fox.

In agricultural environments the importance of the fox as a pest of economic significance has varied according to numbers of prey and changes in animal husbandry practices. A study by Conova and Rosa (1993) on the diet of foxes on agricultural land in the Western Po Plain of northwest Italy found that birds and small mammals made up more than 60% of their diet. Game birds such as mallards (Anas plutyrhynchos) and pheasants (Phasianus colchicus) along with domestic birds were also preyed upon. Lambs are more susceptible to losses than poultry, since they are very numerous and widely dispersed, in some areas they suffer from poor husbandry and are exposed to severe climatic conditions. They have no defence and no means of freeing from the fox. A lamb is entirely dependant upon its mother for protection (Llyod,1980)

In most habitats scavenging is important. In upland regions of West Scotland the fox was found to scavenge in an agricultural environment; however in this habitat other food sources were scarce. Foxes fed largely on sheep carrion and field voles, supplemented by deer carrion, rabbits and birds (Hewson, 1984).

Wherever the fox lives it is an opportunist, this is amply demonstrated by its diet in urban areas. The predatory role of urban fox has not been abandoned. The principal constitutes of the diet of foxes in Oxford city included birds, small mammals invertebrates and fruit (Doncaster, 1990). These were found in similar proportions in the diet of a rural population situated 6km from Oxford city (MacDonald, 1981). However the urban fox supplements its diet with a variety of scavenged food, much of which the rural fox would rarely encounter.

It has been found that urban and suburban foxes in London have a broadly similar diet to foxes in Oxford. Scavenged items comprised 37% of the diet of foxes in London (Harris, 1981) compared to 35% in Oxford (Doncaster, 1990). Foxes in Oxford, however, ate more earthworms (27% as opposed to 12%) and fewer birds and insects. Doncaster (1990) also found that at some sites where food was provided by residents, foxes were highly selective, discarding some edible items in preference for others. 

5. Impact on Prey

In the British Isles range expansion by Red Foxes has raised concerns for seabird and wader colonies on both islands and mainland. On the Isle of Man (Macdonald & Halliwell, 1994) and Anglesey (Lloyd, 1980; pp. 28-29) Foxes introduced deliberately by humans have become established and pose a potential threat to groundnesting bird populations. Fox predation at tern nesting colonies (Sterna albzjkons, S. sandvicensis) on the Norfolk coast (Musgrave, 1993), and amongst nesting Eider ducks in eastern Scotland (Wilson, 1990) is a serious concern for conservationists. In both cases, foxes had been absent or at very low densities in these areas, probably as a result of intensive control by gamekeepers and professional fox-hunters (Middleton, 1936; Hewson & Kolb, 1973). Losses to the urban fox are minimal; in one area of high fox density it has been estimated hat 0.7% of cats and 7% of other pets are killed by foxes each year. However losses could be avoided by improved hourisng.

6. Mortality

6.1 Predators of the fox

The fox has few natural predators. In rural areas of England cubs are often killed at earths by golden eagles (Picture 1). Golden eagles can lift a maximum of four or five kilograms (9 - 11 lbs) - adult male foxes average around 7kg (15 ½ lbs), while females average 5 ½ kg (12 lbs), suggesting that only young foxes are taken by these raptors.   In rare cases adults can be killed by badgers, but cubs are usually affected by badger predation. In Europe, wolves (Canis lupus) and lynx (Lynx lynx) will take foxes if the opportunity arises.   Long-tailed weasels (Mustela frenata), ermine (Mustela erminea), skunks (Mephitis mephitis), mink (Mustela vison) and snakes may take very young fox cubs in the US. In an urban environment dogs are a significant predator of young cubs and will also occasionally kill adults (514)

www.flickr.com/photos/spkaine/3222985713/

6.3. Disease.

Urban foxes due to their higher densities and closer proximity are more susceptible to epizootic diseases such as mange and rabies (Lloyd, 1980?). Until recently, fox numbers were largely stable in urban areas. During the 1990s a parasitic disease called sarcoptic mange spread across most of mainland Britain, causing declines in both rural and urban foxes. With higher densities in urban areas, the decline was more noticeable and in some populations, more than 95% of all individuals died. Despite this, populations are recovering slowly.

Harris (1977b) demonstrated that spinal arthritis (sponodylosis deformans), was present in a very high proportion of urban foxes with an infection level of 34.5%. The average age of the foxes used in the study was only one year nine months. It is thought that development of this disease is related to their diet. Fox (1939) suggested that the situation in urban foxes is unusual; however this has not yet been confirmed by reference to large collections of skeletal material from other populations.

6.2. Human induced mortalities

In both urban and rural populations humans are responsible for a high proportion of fox deaths. In urban areas road traffic is the main cause of fox mortalities (Table 1) (Baker, 2004; Harris and Smith 1987). In 2004, 58% of fox deaths in Bristol were road deaths; with the majority foxes being killed on major category roads (e.g. motorways, A-roads) (Baker, 2004). This figure is in agreement with the 62% of road deaths recorded in 1987 by Harris and smith.

Adults

Cubs

Cause of death

Males

N=473

Females

N=303

Males

N=431

Females

N=429

Road accidents

60.2

63.1

62.7

65.8

Shot

5.8

3.1

0.4

0.4

Snared

3.9

4.3

1.6

0.9

Trapped

2.7

2.4

0.0

0.0

Dug Out

2.1

3.7

7.4

5.3

Killed by lurchers

3.8

3.1

1.2

2.7

Gassed

0.0

0.0

0.0

0.0

Disease

8.9

11.2

5.9

7.9

Deserted cubs

0.0

0.0

1.2

2.7

Fights

3.3

2.2

7.1

9.2

Parturition

0.0

0.4

0.0

0.0

Trains

1.4

0.8

0.0

0.4

Misadventure

1.4

1.6

3.9

3.5

Unknown

6.5

4.1

8.6

3.5

Table 3: Cause of death for foxes in Bristol. The figures are given as percentages and should be taken to indicate the relative importance of the different mortality factors in each city; they simply indicate the source of the material (adapted from Harris and Smith, 1987)

Similar mortality rates can be seen in rural areas where the majority of deaths are caused by culling and hunting of foxes. In a survey of three rural regions in England foxes were culled in 70 - 95% of farms (Reynolds and Tapor, 1996?). Hunting with dogs took a various forms before the introduction of the Hunting Act in 2004: approximately 200 registered packs of foxhounds killed 21,000 - 25,000 foxes annually. 55,000 were dug out with terriers that were introduced into dens and 10,000 were killed by lurchers (Harris and Yalden, 2008).

7. Social organisation and Behaviour

7.1 Territories

Davies (1978) recognises territoriality where "animals are spaced further apart than would be expected from a random occupation of suitable habitats". Between regions the size of fox territory varies largely depending on their habitat; in hill areas of Scotland territories can be up to 4000ha (811); in rural Dorset it has been averaged at 270ha (1092) and as 520ha in Sitka spruce populations (999). In urban areas territories may be as small as 8.5ha, this is due to availability anthropogenic food sources and the higher density of foxes living in cities. In Bristol the mean territory size is 27ha (57, 512. 1372), 39 ha in Oxford (305, 839) and 100ha in Edinburgh (720)

The drifting movement of territories is unique among foxes and has been studied in Oxford. Movement of home ranges may be a behavioural adaptation that has developed since the invasion of foxes into urban areas. The average amount of food available over an area of a city is usually higher than in a similarly sized rural area, but there is also a much greater variance in food availability. Foxes must regularly explore new areas and re-explore old ones in order to make the best use of the resources in an urban environment. In a large rural home range this activity would not be viable as it would require far too much energy; this strategy survives and prospers in cities because of the high density of different habitat patches.

7.2. Relation with Humans

Foxes have had a very mixed relationship with humans. They are generally unpopular with rural communities; unwelcome to gamekeepers, shepards and the majority of farmers (Reynolds and Tapor, 1996). Fox culling in rural Britain is undertaken by several disparate interest groups. The key reason for farmers' involvement in fox culling is the protection of livestock or poultry. Gamekeepers also commonly undertake culling; this is primarily aimed towards protecting game on relatively large farms. In rural areas fox hunting as a sport is often a substantial interest. In some cases landowners and gamekeepers curtail their culling effort to ensure sufficient foxes are available for hunting (Heydon and Reynolds, 2000).

In urban areas foxes are welcomed by most residents and are often supported through deliberate feeding by householders. This is a major area of fox-human interaction. Feeding of foxes can lead to changes in their territory size, as was seen in Bristol where c10% of householders fed foxes (57). Damage caused by foxes in urban areas is generally slight (Harris and Yalden, 2008). During the 1970's and 80's there was a large reduction in the number of foxes killed by the local authority this was due to their increasing popularity in British cities such as London (Harris and Yaldin, 2008). Fox predation on domestic pets is a source of problems between humans and foxes. To find out how many people had lost pets to foxes Harris (1981b) questioned 5,191 households in Bristol during his study of food preference in suburban foxes. Of the households that owned cats only 2.7% had lost a cat to foxes, and most of the cats lost were kittens. In outdoor gardens accessible to foxes, families who kept pets other than cats or dogs, had lost of 8.0% pets to foxes within the past year, and 51.1% had lost a pet more than a year prior to the survey.

8. Discussion

Foxes are found anywhere with adequate food and shelter, from as far south as the Himalayas to the deserts of North Africa and the barren ice valley of the Arctic. Since foxes have exploited every other suitable habitat, it would be surprising if they had not become city-dwellers. It has been suggested by Mac Donald and Nedwick (1982) that there is no strict division between rural and urban foxes; radio tracked foxes regularly commuted between urban and rural areas. Nevertheless, living in the city requires special adaptations, and many anecdotal observations reveal that foxes indeed have adapted to this exceptional environment. However further research is needed into resource exploitation and genetic structure of the urban fox population.

Where ever the fox lives it is an opportunist, this is amply displayed by its diet. The urban fox has not abandoned its predatory role, The principal constitutes of the diet of foxes in Oxford city included birds, small mammals invertebrates and fruit (Doncaster, 1990) but it is augmented by an immense variety of scavenged food, much of which the country fox would scarsely ever encounter. The picture of urban fox diet that has emerged is that it is behaving no differently from rural foxes , except that the scene is different. The same controversy over predation on man's livestock exists in both areas, but in urban areas substitutes cats for lanbs and domestic birds for poultry. Possibly the only large - scale difference is the more regular supply of scavemged foods and the greater availability (though not necessarily abundance) of earthworms on the short swards of domestic lawns than on rougher rural pastures.

The distribution of the urban fox is determined by the availability of suitable daytime refugee of whatever form, whether it be a pile of uncut timber in s timber yard, an dearth under a garden shed, a lying - up placeunder the platform of a suburban railway station or an earth in a rairway cutting. How far the foxes move during their nocturnal wanderings is not known but, as with rural foxes, doubtless their habitats are determined by the availabily and distribution of food and by competition for it according to the density of foxes in an area - more food in urban habitat more densly populated areas.

In urban areas where dense populations of foxes live in close proximity there must be greater social involvement than in the less associated rural fox communities. But in high-density rural fox communities such close shoulder rubbing probably also exists. The situation in urban areas is probably a normal behavioural adaptation to circumstances common in both urban and rural dwelling foxes. The entire way of life of the urban fox, including their behaviour is essentially no different from that of the rural fox. A fox is a fox whether it be urban or rural, British or Japanese and behavioural or physiological differences observed in different places all seen to fall within the known range of response of the fox to external or environmental stimuli. However, the features which determine the distribution and abundance may be different for urban foxes; food availability is usually the most important limiting factor in most fox communities, but in some urban areas it might be the availability to cover which is at premium.

In towns and cities foxes have provided thousands of people with a blissful connection to the natural world that is often very difficult to come by.  

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