Assessment strategies are a vital factor in game theoretical models of contests. In contests animals may engage in mutual assessment; where individuals assess both their own and their opponents resource holding potential (RHP) and make decisions based on estimated differences (Prenter et al, 2006; Briffa, 2008). Alternatively, they may partake in self-assessment, in which individuals set thresholds based on their own RHP (Prenter et al, 2006; Briffa, 2008). Using a statistical methodology which enables the distinction between assessment strategies, the study examined contests in Phidippus clarus, a common jumping spider.The study had three main aims: to determine whether substrate-borne signals are important in aggressive contests, the assessment strategies used in contests, and the factors that decide contest outcomes.
Adult and penultimate male and female P. clarus were collected. They were individually housed in the laboratory for a minimum of 4 days to allow them to acclimate prior to use. The experimental arena was a plastic cylinder with petroleum jelly on the inside of the wall to prevent spiders escaping. In order to avoid visual disturbances, an opaque paper ring was placed around the cylinder. Graph paper was used as the arena floor, this allowed movement to be measured. It was replaced after every two trials to prevent chemical cue build up. An empty female nest was placed in the center of the arena.
To begin with a removable barrier split the arena into two equal sections. Randomly selected males were placed in separate halves and left to acclimate for 5 minutes. The barrier enabled acclimation and removed potential ownership effects. Contests were observed and substrate-borne vibrations were recorded using a laser droppler vibrometer. Contests were terminated after three bouts, a male was considered to have won a bout when the rival male turned away and retreated more than two body lengths. Male behaviours during aggressive interactions were divided into two phases: the precontact phase and the contact phase. The contact phase began when the two spiders started to “leg fence”. During the precontact phase males produced substrate-borne signals. The signals generally preceded movement toward rivals and rarely preceded retreat. Following the contests, males were weighed and digitally photographed to measure patella-tibia length and cephalothorax width. These measurements were used as an indicator of size. A range of statistical analysis was performed on the data.
A statistical methodology outlined by Taylor and Elwood (2003) and Morrell et al (2005) was used to distinguish assessment strategies. The results indicated that contest duration, particularly contact phases, were based predominantly on self-assessment and to a lesser degree mutual assessment. It was suggested that males may shift between self-assessment and mutual assessment as more information becomes available or more reliable. In the case of partial mutual assessment, as more rival assessment occurs, a negative correlation will grow between winner weight and contest duration (Prenter et al, 2006). The study found a nonsignificant negative relationship between winner weight and contest duration. This is congruous with partial mutual assessment.
It was suggested that relying more heavily on self-assessment to determine contest duration may be an economical strategy that avoids the costs of mutual assessment. Mutual assessment requires energetic demands to detect and process a rivals signals, as well as needing time to process the information in order to make accurate decisions. These costs would be heightened if the signals were unreliable. Hence, self-assessment enables the individual to pay only the costs they are willing to but maintain a high probability of winning against inferior rivals.
The male jumping spiders used multimodal signals during aggressive interactions: visual and substrate-borne. Substrate-borne vibrations appeared to be of particular importance, given that the number of vibratory signals accurately predicted the contest outcome. More actively signaling males were more likely to win.Â Additionally, precontact phase duration was based on relative vibration behaviour. Males which vibrated at similar rates had shorter precontact phases.
Figure.1 Effect of experience on contests. (a) Differences between contest phase duration in different bouts. Both precontact and contact phase duration were significantly reduced after initial contests. (b) Difference between vibrational signalling between different contest bouts. **P < 0.001. (Elias et al, 2008)
53/56 of the males that won the first bout went on to win all three bouts. The study found contest experience affected male’s signalling rate. While winners signalled repeatedly at a similar rate, losers significantly decreased the rate at which they signalled after losing the first bout (Fig. 1b). As well as this, experience affected the time that males spent in contest. Both precontact and contact phases were notably shorter in the second and third bouts (Fig.1a). This indicates that experience effects are important for multiple contests with the same opponent in P. clarus. In the field, males would most likely escape after losing a single contest, so repeated bouts with the same individual may be rare. However, these results important because they highlight that experience, especially losing experience, can influence subsequent behaviours. Following these results an area that needed more research is the impact of experience on future contests with new rivals and the duration of these effects.
This is addressed in a later paper by Kasumovic et al (2010). They found that winner and loser effects have a similar magnitude, but loser effects persist longer. They also found previous experience alters actual fighting ability. They suggested that experience should be integrated into models, particularly when competitive signals or traits are unreliable.
Arnott and Elwood (2009) also wrote a subsequent paper which encouraged game theorists to update models. The paper explored how the abilities of contestants to assess RHP influences fights. The paper cited Elias et al (2008) to support the existence of partial mutual assessment. They stated that strategies, such as partial mutual assessment, point to limitations of current game theory models. Arnott and Elwood’s (2009) work has been influential, with further work finding winner and loser effects change with age, which is often a disregarded factor in studies (Fawcett and Johnstone, 2010).
Arnott, G. and Elwood, R.W. (2009) ‘Assessment of fighting ability in animal contests’, Animal Behaviour, 77(5), pp. 991-1004.
Bridge, A.P., Elwood, R.W. and Dick, J.T.A. (2000) ‘Imperfect assessment and limited information preclude optimal strategies in male-male fights in the orb-weaving spider Metellina mengei’, Proceedings of the Royal Society B: Biological Sciences, 267(1440), pp. 273-279.
Briffa, M. (2008) ‘Decisions during fights in the house cricket, Acheta domesticus: Mutual or self assessment of energy, weapons and size?’, Animal Behaviour, 75(3), pp. 1053-1062.
Elias, D.O., Kasumovic, M.M., Punzalan, D., Andrade, M.C.B. and Mason, A.C. (2008) ‘Assessment during aggressive contests between male jumping spiders’, Animal Behaviour, 76(3), pp. 901-910.
Fawcett, T.W. and Johnstone, R.A. (2010) ‘Learning your own strength: Winner and loser effects should change with age and experience’, Proceedings of the Royal Society B: Biological Sciences, 277(1686), pp. 1427-1434.
Kasumovic, M.M., Elias, D.O., Sivalinghem, S., Mason, A.C. and Andrade, M.C.B. (2010) ‘Examination of prior contest experience and the retention of winner and loser effects’, Behavioral Ecology, 21(2), pp. 404-409.
Morrell, L.J., Backwell, P.R.Y. and Metcalfe, N.B. (2005) ‘Fighting in fiddler crabs Uca mjoebergi: What determines duration?’, Animal Behaviour, 70(3), pp. 653-662.
Prenter, J., Elwood, R.W. and Taylor, P.W. (2006a) ‘Self-assessment by males during energetically costly contests over precopula females in amphipods’, Animal Behaviour, 72(4), pp. 861-868.
Prenter, J., Elwood, R.W. and Taylor, P.W. (2006b) ‘Self-assessment by males during energetically costly contests over precopula females in amphipods’, Animal Behaviour, 72(4), pp. 861-868.
Taylor, P.W. and Elwood, R.W. (2003) ‘The mismeasure of animal contests’, Animal Behaviour, 65(6), pp. 1195-1202.
Assessment of Mangroves Species Vulnerable to Human Threats
TITLE: ASSESSMENT OF MANGROVES SPECIES VULNERABLE TO HUMAN THREATS AT MBEGANI AND MLIGOTIN VILLAGE.
1.0 INTRODUCTION 1.1 BACKGROUND INFORMATION
Mangroves are woody plants that grow at the interface between land and sea. occur worldwide in the tropics and subtropics, mainly between latitudes 25° N and 25° S. they are salt tolerant trees, also called halophytes, and are adapted to life in harsh coastal conditions. They contain a complex salt filtration system and complex root system to cope with salt water immersion and wave action. They are adapted to the low oxygen conditions of waterlogged mud. The word “mangrove” is usually considered a compound of the Portuguese word “mangue” and the English word “grove.” The term “mangrove” often refers to both the plants and the forest community. To avoid confusion, Macnae (1968) proposed that “mangal” should refer to the forest community while “mangroves” should refer to the individual plant species. Mangrove forests are sometimes called “tidal forests”, “coastal woodlands”, or “oceanic rain forests.” Mangrove swamps are found in tropical and subtropical tidal areas. Areas where mangal occurs include estuaries and marine shorelines. High tide brings in salt water, and when the tide leave, solar evaporation of the seawater in the soil leads to further increases in salinity. The return of tide can flush out these soils, bringing them back to salinity levels comparable to that of seawater.
At low tide, organisms are also exposed to increases in temperature and desiccation, and are then cooled and flooded by the tide. Thus, for a plant to survive in this environment, it must tolerate broad ranges of salinity, temperature, and moisture, as well as a number of other key environmental factors thus only a select few species make up the mangrove tree community. About 110 species are considered “mangroves”, in the sense of being a tree that grows in such a saline swamp.
Mangrove ecosystems are estimated to cover 150 000 km2 world-wide (Diop 1992, 1993). Mangroves can be found in over 118 countries and territories in the tropical and subtropical regions of the world the largest percentage of mangroves is found between the 5° N and 5° S latitudes. Approximately 75% of world’s mangroves are found in just 15 countries. Asia has the largest amount (42%) of the world’s mangroves, followed by Africa (21%), North/Central America (15%), Oceania (12%) and South America (11%).
Africa has about 35 000 km2 of mangrove ecosystem (Diop 1992, 1993), Nigeria has largest mangrove area about 1mln ha. East Africa consist of mangroves swamps along the Indian Ocean coast of East Africa in southern Mozambique, Tanzania, Kenya and southern Somalia.
Delta of Zambezi in Mozambique and Rufiji River in Tanzania are large area of mangroves which can extend as far as 50 km inland, as well as smaller areas along the coast.
The mangroves of Bagamoyo District form a more-or-less continuous band along the 100-km coastline from Saadani tonear Kitame salt works, and then from Ruvu Riverto Mpiji River. They cover an area of 5635 ha (Semesi, 1991).The main mangrove stands are found along Wami River, 862 ha, Utondwe creek, 834 ha, Ruvu River, 2123 ha, and south of Bagamoyo to Mpiji River, 809ha. By 1989, clear-cut areas and salt panscovered 1639 ha (Semesi, 1991) and water in the creeks covered 812ha.
1.2 STATEMENT OF THE PROBLEM
Increase in population leads to distraction of mangroves swamps which in turn has great impact to marine environment since mangroves help in break oceanic waves also provide nursery area and habitat to some marine organism. Understanding which species of mangroves are vulnerable to human threats and why is more important and helpful in establishment of conservation plant of particular species.
1.3 GENERAL OBJECTIVES
Increase awareness among the people about important of mangroves species and how various human activities can distract mangroves ecosystem.
1.4 SPECIFIC OBJECTIVES
To identify the most threatened mangroves species found in mbegani and mlingotini village
To assess various human activities that threats mangroves species
1.5.1 Null hypothesis.
There is no mangroves species vulnerable to human threats at mbegani and mlingotini village.
1.5.2 Alternative hypothesis.
There are mangroves species vulnerable to human threats at mbegani and mlingotini village.
1.6 SIGNIFICANCE OF THE STUDY
Findings in this study would enhance awareness among the local community about mangroves species and their important to the local community. Also the findings of this study would create awareness among people about various activities performed by local community which threats mangroves species. This study will encourage natural resource management by local community and enhance formulation of village policy about environment conservation.
2 LITERATURE REVIEW According to Spalding 1997 mangroves forest disappear everyday all over the world. It was approximated 18.1 million km2 of mangroves forest cover worldwide but according to FAO recent study show that mangroves forest is decline to 15 million km2. Developing countries consist 90% of mangroves forest growing worldwide and most of them critically endangered and nearly extinction in 26 countries. According to duke 2007 the experts of world mangroves provide their view that the survival of mangroves in long term is at great risk due to fragmentation of habitat and that the survive offered by the mangroves may likely to be totally lost within 100 years. Many mangroves areas are under pressure of human especially those grow along humid sheltered tropical coastline. A side from man-made pressure the mangroves also degraded due environmental stress. Estimate show that global loss annually is one million ha and some region in dangers of complete collapse (kathiresan and Bingham 2001). Most people cause destruction of mangroves either by knowingly or not knowingly the value of mangroves. Livehood, biodiversity loss and fishery resource are reduced to mangroves loss, also decline in population of marine mammals like manatees and dugongs contributed much by loss of mangroves (k. kathiresan 2001). Rates at which mangroves loss is much higher compared to that of tropical forest and coral reef. 7million hectares of mangroves loss worldwide which is equivalent to two years loss of all forest system globally (k. kathiresan and Bingham 2001).
Study show that man-made activities contribute much to the destruction of mangroves species which pose significant threats examples of those activities are;
Urbanization; inhabitation of human to many areas cause coast mangroves to be cleared. Areas which experience this are Singapore, Jakarta, Bangkok, Mumbai, Lagos, and free town.
Agriculture; mangroves destroyed because of agriculture activities example regions of largest delta in the world between India and Bangladesh. According to kathiresan 2001 the mangrove areas are deforested and reclaimed with rainwater to drain the salt content of the soil and these areas are protected from seawater intrusion by constructing embankments. Once the salt is leached to sufficient level, the land is cultivated either with paddy or coconut.
Aquaculture practices; in several countries aquaculture contribute in large scale destruction of mangroves. In 1968 and 1983, 237000 ha of mangroves were loss for pond construction in Philippines which is half of national mangroves (Fernandez1978). According to kathiresan One major issue associated with the farms located in mangrove habitats is acidification of pond waters that kills aquatic organisms.
Cutting for timber, fuel and charcoal; due to its higher calorific value twing of mangroves are used for firewood. Rich in phenol enable mangroves wood to highly resist deterioration as is widely used as timber and their suitable for chipboard and quality paper industry.
Oil pollution; Oil or gas exploration, petroleum production, and accidents by large oil tankers cause significant damage to mangrove ecosystems. To cite an example, NigeriaÊ¹s richest oil wells are situated close to inshore where rich mangroves once existed. Similarly oil tanker accidents in the Gulf of Mexico and in the Caribbean areas resulted in oil spillage that severely damages the coastal systems. As a result, the entire mangrove ecosystem got affected, causing defoliation of trees, mortality of all sessile and benthic organisms and contamination of many water fowls. Once the mangrove forest is affected by oil pollution, it will take a long time of at least 10 years for recovery of the forest.
3 RESEARCH METHODOLOGY 3.1 STUDY AREA
This work will be conducted in pwani region in Bagamoyo district at mbegani and mlingotini villages.Bagamoyo is one of the 6 districts of the Pwani Region. It is bordered to the North by the Tanga Region, to the West by the Morogoro Region, to the East by the Indian Ocean and to the South by the Kibaha District.
According to the 2012 Tanzania National Census, the population of the Bagamoyo District was 311,740. Mbegani and mlingotini villages found in zinga ward which its geographical coordinates are 6° 31′ 0″ South, 38° 59′ 0″ East.
3.2 STUDY MATERIAL
Material which will be used in this study are:
Note book and pencil which will be used to take record.
Rain boots which will be used to protect legs from protruding mangroves root.
Gloves which will be used for hands protection.
3.3 DATA COLLECTION TECHNIQUES
During this work data will be collected by simple prepared questionnaires and through observation.
3.4 DATA ANALYSIS
Gathered information from this study will be analyzed by Microsoft excel.